A conjugated polyelectrolyte (CPE) based on a poly(phenylene ethynylene) backbone designed to avoid interchain aggregation was adsorbed onto n-type zinc oxide (0001) single crystals. Photophysical, atomic force microscopy, and photoelectrochemical measurements confirm the absence of aggregation in solution and on ZnO single-crystal surfaces. At high surface coverage on the ZnO surface, individual polymer chains are resolved, and photocurrent efficiency measurements suggest that charge injection occurs with modest efficiency.Keywords: AFM; atomic force microscopy; conjugated polymer; DSSC; dye-sensitized solar cell; metal oxide electrodes;

Pt-doped mesoporous Ti3+ self-doped TiO2 (Pt–Ti3+/TiO2) is in situ synthesized via an ionothermal route, by treating metallic Ti in an ionic liquid containing LiOAc, HOAc, and a H2PtCl6 aqueous solution under mild ionothermal conditions. Such Ti3+-enriched environment, as well as oxygen vacancies, is proven to be effective for allowing the in situ reduction of Pt4+ ions uniformly located in the framework of the TiO2 bulk. The photocatalytic H2 evolution of Pt–Ti3+/TiO2 is significantly higher than that of the photoreduced Pt loaded on the original TiO2 and commercial P25. Such greatly enhanced activity is due to the various valence states of Pt (Ptn+, n = 0, 2, or 3), forming Pt–O bonds embedded in the framework of TiO2 and ultrafine Pt metal nanoparticles on the surface of TiO2. Such Ptn+–O bonds could act as the bridges for facilitating the photogenerated electron transfer from the bulk to the surface of TiO2 with a higher electron carrier density (3.11 × 1020 cm–3), about 2.5 times that (1.25 × 1020 cm–3) of the photoreduced Pt–Ti3+/TiO2 sample. Thus, more photogenerated electrons could reach the Pt metal for reducing protons to H2.Keywords: H2 evolution; oxygen vacancies; Pt doping; Ti3+; TiO2;

A series of variable band-gap donor–acceptor–donor (DAD) chromophores capped with platinum(II) acetylide units has been synthesized and fully characterized by electrochemical and photophysical methods, with particular emphasis placed on probing triplet excited state properties. A counter-intuitive trend of increasing fluorescence quantum efficiency and lifetime with decreasing excited state energy (optical gap) is observed across the series of DAD chromophores. Careful study of the excited state dynamics, including triplet yields (as inferred from singlet oxygen sensitization), reveals that the underlying origin of the unusual trend in the fluorescence parameters is that the singlet–triplet intersystem crossing rate and yield decrease with decreasing optical gap. It is concluded that the rate of intersystem crossing decreases as the LUMO is increasingly localized on the acceptor unit in the DAD chromophore, and this result is interpreted as arising because the extent of spin–orbit coupling induced by the platinum heavy metal centers decreases as the LUMO is more localized on the acceptor. In addition to the trend in intersystem crossing, the results show that the triplet decay rates follow the Energy Gap Law correlation over a 1.8 eV range of triplet energy and 1000-fold range of triplet decay rates. Finally, femtosecond transient absorption studies for the DAD chromophores reveals a strong absorption in the near-infrared region which is attributed to the singlet excited state. This spectral band appears to be general for DAD chromophores, and may be a signature of the charge transfer (CT) singlet excited state.

Dye-sensitized solar cells (DSSCs) based on a donor–acceptor–donor oligothienylene dye containing benzothiadiazole (T4BTD-A) were cosensitized with dyes containing cis-configured squaraine rings (HSQ3 and HSQ4). The cosensitized dyes showed incident monochromatic photon-to-current conversion efficiency (IPCE) greater than 70% in the 300–850 nm wavelength region. The individual overall conversion efficiencies of the sensitizers T4BTD-A, HSQ3, and HSQ4 were 6.4%, 4.8%, and 5.8%, respectively. Improved power conversion efficiencies of 7.0% and 7.7% were observed when T4BTD-A was cosensitized with HSQ3 and HSQ4, respectively, thanks to a significant increase in current density (JSC) for the cosensitized DSSCs. Intensity-modulated photovoltage spectroscopy results showed a longer lifetime for cosensitized T4BTD-A+HSQ3 and T4BTD-A+HSQ4 compared to that of HSQ3 and HSQ4, respectively.Keywords: benzothiadiazole dye; co-sensitization; dye-sensitized solar cell; incident photon to current conversion efficiency; squaraine dye

The ligand 5-PO3H2-2,2′:5′,2″-terthiophene-5-trpy, T3 (trpy = 2,2′:6′,2″-terpyridine), was prepared and studied in aqueous solutions along with its metal complex assembly [Ru(T3)(bpy)(OH2)]2+ (T3-Ru-OH2, bpy = 2,2′-bipyridine). T3 contains a phosphonic acid group for anchoring to a TiO2 photoanode under aqueous conditions, a terthiophene fragment for light absorption and electron injection into TiO2, and a terminal trpy ligand for the construction of assemblies comprising a molecular oxidation catalyst. At a TiO2 photoanode, T3 displays efficient injection at pH 4.35 as evidenced by the high photocurrents (∼350 uA/cm2) arising from hydroquinone oxidation. Addition of [Ru(bpy)(OTf)][OTf]2 (bpy = 2,2′-bipyridine, OTf– = triflate) to T3 at the free trpy ligand forms the molecular assembly, T3-Ru-OH2, with the oxidative catalyst fragment: [Ru(trpy)(bpy)(OH2)]2+. The new assembly, T3-Ru-OH2, was used to perform efficient light-driven oxidation of phenol (230 μA/cm2) and benzyl alcohol (25 μA/cm2) in a dye-sensitized photoelectrosynthesis cell.Keywords: C−H activation; dye-sensitized photoelectrosynthesis cell; dye-sensitized solar cell; organic alcohol oxidation; solar fuels;

A corrugated organic light emitting diode (OLED) with enhanced light extraction is realized by incorporating a corrugated composite electron transport layer (ETL) consisting of two ETLs with different glass transition temperatures. The morphology of the corrugated structure is characterized with atomic force microscopy. The results show that the corrugation can be controlled by the layer thicknesses and annealing temperature. Compared with the control planar device, the corrugated OLED shows a more than 35% enhancement in current efficiency from 31 cd/A to 43 cd/A and a 20% enhancement in external quantum efficiency from 10% to 12% at 100 cd/m2. In addition, the corrugated OLED also has a greatly improved operational stability. The LT90 lifetime of a device operated at 1000 cd/m2 is improved greater than 100-fold in the corrugated OLED.

We report a systematic study that explores how the triplet excited state is influenced by conjugation length in a series of benzothiadiazole units containing donor–acceptor–donor (DAD)-type platinum acetylide oligomers and polymer. The singlet and triplet excited states for the series were characterized by an array of photophysical methods including steady-state luminescence spectroscopy and femtosecond–nanosecond transient absorption spectroscopy. In addition to the experimental work, a computational study using density functional theory was conducted to gain more information about the structure, composition, and energies of the frontier molecular orbitals. It is observed that both the singlet and triplet excited states are mainly localized on a single donor–acceptor–donor unit in the oligomers. Interestingly, it is discovered that the intersystem crossing efficiency increases dramatically in the longer oligomers. The effect is attributed to an enhanced contribution of the heavy metal platinum in the frontier orbitals (HOMO and LUMO), an effect that leads to enhanced spin–orbit coupling.

This study explores the effect of substitution of selenium (Se) for sulfur (S) on the photophysical properties of a series of π-conjugated donor–acceptor–donor chromophores based on 4,7-bis(2-thienyl)-2,1,3-benzothiadiazole (TBT). The effect of Se substitution is studied systematically, where the substitution is in the thiophene donors only, the benzothiadiazole acceptor only, and in all of the positions. The fluorescence quantum yield decreases with an increase in Se substitution. Nanosecond–microsecond transient absorption and singlet oxygen sensitization experiments show that the effect of Se is due to an increase in the rate and efficiency of intersystem crossing with increased Se substitution. The relationship between intersystem crossing efficiency and heteroatom substitution pattern shows that the effects are largest when the heavy atom Se is in the acceptor benzothiadiazole unit. DFT calculations support the hypothesis that the effect arises because the LUMO is concentrated in the acceptor moiety, enhancing the spin–orbit coupling effect imparted by the Se atom.

Layer-by-Layer (LbL) polyelectrolyte self-assembly occurs by the alternate exposure of a substrate to solutions of oppositely charged polyelectrolytes or polyions. Here, we report the application of LbL to construct chromophore–catalyst assemblies consisting of a cationic polystyrene-based Ru polychromophore (PS-Ru) and a [Ru(tpy)(2-pyridyl-N-methylbenzimidazole) (OH2)]2+ water oxidation catalyst (RuC), codeposited with poly(acrylic acid) (PAA) as an inert polyanion. These assemblies are deposited onto planar indium tin oxide (ITO, Sn:In2O3) substrates for electrochemical characterization and onto mesoporous substrates consisting of a SnO2/TiO2 core/shell structure atop fluorine doped tin oxide (FTO) for application to light-driven water oxidation in a dye-sensitized photoelectrosynthesis cell. Cyclic voltammetry and ultraviolet–visible absorption spectroscopy reveal that multilayer deposition progressively increases the film thickness on ITO glass substrates. Under an applied bias, photocurrent measurements of the (PAA/PS-Ru)5/(PAA/RuC)5 LbL films formed on FTO//SnO2/TiO2 mesoporous core–shell electrodes demonstrate a clear anodic photocurrent response. Prolonged photoelectrolysis experiments, with the use of a dual working electrode collector–generator cell, reveal production of O2 from the illuminated photoanode with a Faradaic efficiency of 22%. This is the first report to demonstrate the use of polyelectrolyte LbL to construct chromophore–catalyst assemblies for water oxidation.

This article reports an investigation of the photophysical properties and the light- and dark-biocidal activity of two poly(phenyleneethynylene) (PPE)-based conjugated polyelectrolytes (CPEs) bearing cationic imidazolium solubilizing groups. The two polymers feature the same PPE-type backbone, but they differ in the frequency of imidazoliums on the chains: PIM-4 features two imidazolium units on every phenylene repeat, whereas PIM-2 contains two imidazolium units on every other phenylene unit. Both polymers are very soluble in water and polar organic solvents, but their propensity to aggregate in water differs with the density of the imidazolium units. The polymers are highly fluorescent, and they exhibit the amplified quenching effect when exposed to a low concentration of anionic electron-acceptor anthraquinone disulfonate. The CPEs are also quenched by a relatively low concentration of pyrophosphate by an aggregation-induced quenching mechanism. The biocidal activity of the cationic imidazolium CPEs was studied against both Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus bacteria in the dark and under blue-light illumination. Both polymers are effective biocides, exhibiting greater than 3 log kill with 30–60 min of light exposure at concentrations of ≤10 μg mL–1.Keywords: antimicrobial polymers; biocides; conjugated polyelectrolytes; ionic liquids; singlet oxygen; triplet state

Mitigation of bacterial adhesion and subsequent biofilm formation is quickly becoming a strategy for the prevention of hospital-acquired infections. We demonstrate a basic strategy for surface modification that combines the ability to control attachment by microbes with the ability to inactivate microbes. The surface consists of two active materials: poly(p-phenylene ethynylene)-based polymers, which can inactivate a wide range of microbes and pathogens, and poly(N-isopropylacrylamide)-based polymers, which can switch between an hydrophobic “capture” state and a hydrophilic “release” state. The combination of these materials creates a surface that can both bind microbes in a switchable way and kill surface-bound microbes efficiently. Considerable earlier work with cationic poly(p-phenylene ethynylene) polyelectrolytes has demonstrated and characterized their antimicrobial properties, including the ability to efficiently destroy or deactivate Gram-negative and Gram-positive bacteria, fungi, and viruses. Similarly, much work has shown (1) that surface-polymerized films of poly(N-isopropylacrylamide) are able to switch their surface thermodynamic properties from a swollen, relatively hydrophilic state at low temperature to a condensed, relatively hydrophobic state at higher temperature, and (2) that this switch can control the binding and/or release of microbes to poly(N-isopropylacrylamide) surfaces. The active surfaces described herein were fabricated by first creating a film of biocidal poly(p-phenylene ethynylene) using layer-by-layer methods, and then conferring switchable adhesion by growing poly(N-isopropylacrylamide) through the poly(p-phenylene ethynylene) layer, using surface-attached polymerization initiators. The resulting multifunctional, complex films were then characterized both physically and functionally. We demonstrate that such films kill and subsequently induce widespread release of Gram-negative and Gram-positive bacteria.Keywords: bacteria; conjugated polyelectrolyte; kill; PNIPAAm; release

A series of platinum(II) acetylide complexes containing p-phenylenevinylene and moieties end-capped with triphenylamine groups have been incorporated into poly(methyl methacrylate) (PMMA) monoliths for optical power limiting applications. The one- and two-photon photophysical properties were investigated and compared to the photophysical properties in THF. The absolute two-photon absorption cross-section values for the monolith samples were measured and are comparable to the values obtained in solution. In the PMMA monoliths, the complexes retained the important two-photon absorption and reverse saturable absorption properties necessary for optical power limiting via dual mode mechanism, and their strong nonlinear absorption property was demonstrated by the open-aperture Z-scan method. Photostability studies of the p-phenylenevinylene platinum(II) acetylide complexes showed two photodegradation processes: a trans-to-cis isomerization and a singlet-oxygen sensitized self-oxidative cleavage. The photostability of the least photostable complex TPV0 was increased upon incorporation into a PMMA matrix.Keywords: nonlinear absorption; optical power limiting; platinum(II) acetylide; reverse-saturable absorption; two-photon absorption;

This research investigates the modification and dispersion and of pristine multiwalled carbon nanotubes (MWCNTs) through a simple solution mixing technique based on noncovalent interactions between poly(phenylene ethynylene)-based conjugated polyelectrolytes functionalized with cationic imidazolium solubilizing groups (PIM-2 and PIM-4) and MWCNTs. Spectroscopic studies demonstrated the ability of PIMs to strongly interact with and efficiently disperse MWCNTs in different solvents, mainly due to π interactions between the PIMs and the MWCNTs. Transmission electron microscopy and atomic force microscopy revealed the coating of the polyelectrolytes on the walls of the nanotubes. Scanning electron microscopy (SEM) studies confirm the homogeneous dispersion of PIM-modified MWCNTs in the poly(methyl methacrylate) (PMMA) matrix. The addition of 1 wt % PIM-modified MWCNTs to the matrix has led to a significant decrease in DC resistivity of the composite (13 orders of magnitude). The increase in electrical conductivity and the improvement in the thermal and mechanical properties of the membranes containing the PIM-modified MWCNTs is ascribed to the formation of MWCNT networks and cross-linking sites that provided channels for the electrons to move in throughout the matrix and reinforced the interface between MWCNTs and PMMA.Keywords: composites; conjugated polyelectrolytes; CPEs; dispersion; electrical conductivity; multiwalled carbon nanotubes; MWCNTs; PMMA; poly(methyl methacrylate);

Two sets of conjugated polyelectrolytes with different molecular weights (Mn) in each set were synthesized. All polymers feature the same conjugated backbone with alternating (1,4-phenylene) and (2,5-thienylene ethynylene) repeating units, but different linkages between the backbone and side chains, namely, oxy-methylene (-O-CH2-) (P1-O-n, where n = 7, 9, and 14) and methylene (-CH2-) (P2-C-n, n = 7, 12, and 18). They all bear carboxylic acid moieties as side chains, which bind strongly to titanium dioxide (TiO2) nanoparticles. The two sets of polymers were used as light-harvesting materials in dye-sensitized solar cells. Despite the difference in molecular weight, polymers within each set have very similar light absorption properties. Interestingly, under the same working conditions, the overall cell efficiency of the P1-O-n series increases with a decreasing molecular weight while the efficiency of the P2-C-n series remains constant regardless of the molecular weight. Steady state photophysical measurements and dynamic light scattering investigation prove that P1-O-n polymers aggregate in solution while P2-C-n series are in the monomeric state. In P1-O-n series, a higher-molecular weight polymer results in a larger aggregate, which reduces the amount of polymers that are adsorbed onto TiO2 films and overall cell efficiency.Keywords: aggregation; cell efficiency; conjugated polyelectrolytes; dye-sensitized solar cells

An isoindigo based π-conjugated oligomer and polymer that contain cyclometalated platinum(II) “auxochrome” units were subjected to photophysical characterization, and application of the polymer in bulk heterojunction polymer solar cells with PCBM acceptor was examined. The objective of the study was to explore the effect of the heavy metal centers on the excited state properties, in particular, intersystem crossing to a triplet (exciton) state, and further how this would influence the performance of the organometallic polymer in solar cells. The materials were characterized by electrochemistry, ground state absorption, emission, and picosecond–nanosecond transient absorption spectroscopy. Electrochemical measurements indicate that the cyclometalated units have a significant impact on the HOMO energy level of the chromophores, but little effect on the LUMO, which is consistent with localization of the LUMO on the isoindigo acceptor unit. Picosecond–nanosecond transient absorption spectroscopy reveals a transient with ∼100 ns lifetime that is assigned to a triplet excited state that is produced by intersystem crossing from a singlet state on a time scale of ∼130 ps. This is the first time that a triplet state has been observed for isoindigo π-conjugated chromophores. The performance of the polymer in bulk heterojunction solar cells was explored with PC61BM as an acceptor. The performance of the cells was optimum at a relatively high PCBM loading (1:6, polymer:PCBM), but the overall efficiency was relatively low with power conversion efficiency (PCE) of 0.22%. Atomic force microscopy of blend films reveals that the length scale of the phase separation decreases with increasing PCBM content, suggesting a reason for the increase in PCE with acceptor loading. Energetic considerations show that the triplet state in the polymer is too low in energy to undergo charge separation with PCBM. Further, due to the relatively low LUMO energy of the polymer, charge transfer from the singlet to PCBM is only weakly exothermic, which is believed to be the reason that the photocurrent efficiency is relatively low.Keywords: isoindigo; orthometalated platinum; polymer solar cell; transient absorption; triplet state

A series of polystyrene-based light harvesting polymers featuring pendant polypyridyl ruthenium complexes has been synthesized. The polymer backbones were prepared by nitroxide-mediated radical polymerization with a variable average molecular weight (Mn) ranging from ∼5500 to ∼24000 g mol−1. Pendant Ru(II) polypyridyl complexes were grafted to the polymer backbone by azide–alkyne click chemistry to afford chromophore loaded polymers. The resulting polystyrene-based polychromophores with pendant Ru(II) polypyridyl complexes (PS-Ru) were characterized by nuclear magnetic resonance and infrared spectroscopy, confirming the high efficiency of the click grafting. The photophysical and electrochemical properties of the series of PS-Ru polymers were characterized in solution and investigated as a function of polymer chain length and solvent. The electrochemical properties of PS-Ru maintained the characteristics of the individual Ru(II) polypyridyl units. Emission quantum yield and lifetime studies reveal that the metal-to-ligand charge transfer (MLCT) excited states are quenched to a variable extent depending on the molecular weight of the polymers, consistent with intramolecular energy transfer and self-quenching in polymers with longer chain lengths. To support the synthetic effort, molecular dynamics simulations of the polypyridyl ruthenium derivatized polystyrenes in different solvents were conducted.

A series of Au(I) and Pt(II) acetylide complexes of a π-conjugated donor–acceptor–donor (D-A-D) chromophore were studied to develop quantitative structure–property relationships for their photophysical and nonlinear optical properties. The D-A-D chromophore consists of a “TBT” unit, where T = 3-hexyl-2,5-thienylene and BTD = 2,1,3-benzothiadiazole, capped with ethynylene groups. The D-A-D chromophore is functionalized with Au(I)PR3 (R = −Me and −Ph) and trans-Pt(II)(PR3)2-CCPh (R = −Me and −Bu) “auxochromes”. All of the metal complexes were characterized by ground-state absorption, photoluminescence, nanosecond transient absorption, and two-photon absorption (2PA) spectroscopy. The experiments provided quantitative values of the photophysical parameters, including rates for radiative decay and intersystem crossing (ISC), triplet yields, and two-photon absorption cross sections. Pronounced solvatochromism in the fluorescence spectra suggests an enhanced dipole moment in the excited state of the complexes compared to the unmetalated TBT chromophore. The gold complexes feature larger fluorescence quantum yields and longer emission lifetimes compared to platinum. The Pt(II) complexes exhibit enhanced triplet–triplet absorption, reduced triplet-state lifetimes, and larger singlet oxygen quantum yields, consistent with more efficient ISC compared to the Au(I) complexes. When excited by 100 fs pulses, all of the D-A-D chromophores exhibit moderate two-photon absorption in the near-infrared between 700 and 900 nm. The 2PA cross section for the Au(I) complexes is almost the same as the unmetalated D-A-D chromophore (∼100 GM). The Pt(II) complexes exhibit significantly enhanced 2PA compared to the other chromophores, reaching 1000 GM at 750 nm. Taken together, the results indicate that the Pt(II) center is considerably more effective in inducing singlet–triplet ISC and in enhancing the 2PA cross section. This result reveals the greater promise for Pt(II) acetylides in chromophores for temporal and frequency agile nonlinear absorption.

The preparation of Pt(II) complexes of the type trans-L2Pt(Ar)Cl, L2Pt(Ar)2, and L2Pt(Ar)(Ar′) (L = PBu3, Ar = arylene) by CuI catalyzed reaction of cis-(PBu3)2PtCl2 with aryl-stannanes is reported. The reactions proceed at 25–60 °C in moderate to good yields. The reaction is demonstrated to occur with phenyl- and 2-thienyl-stannanes that include a variety of functionality, and all of the resulting Pt-aryl complexes were fully characterized by 1H, 13C, and 31PNMR spectroscopy, as well as mass spectroscopy. Photophysical properties of the L2Pt(Ar)2, and L2Pt(Ar)(Ar′) complexes were measured, including steady-state absorption, photoluminescence, and photoluminescence quantum yields, in order to understand how attachment of the platinum metal influences the excited state properties of the arylene ligands. This work affirms that CuI catalyzed coupling between Ar–SnR3 and L2PtCl2 is a useful platinum–carbon bond formation reaction.

Light harvesting and triplet energy transport is investigated in chromophore-functionalized polystyrene polymers featuring light harvesting and energy acceptor chromophores (traps) at varying loading. The series of precision polymers was constructed via reversible addition–fragmentation transfer polymerization and functionalized with platinum acetylide triplet chromophores by using an azide–alkyne “click” reaction. The polymers have narrow polydispersity and degree of polymerization ∼60. The chromophores have the general structure, trans-[−R–C6H4–C≡C–Pt(PBu3)2–C≡C–Ar], where R is the attachment point to the polystyrene backbone and Ar is either –C6H4–C≡C–Ph or –pyrenyl (PE2-Pt and Py-Pt, respectively, with triplet energies of 2.35 and 1.88 eV). The polychromophores contain mainly the high-energy PE2-Pt units (light absorber and energy donor), with randomly distributed Py-Pt units (3–20% loading, energy acceptor). Photophysical methods are used to study the dynamics and efficiency of energy transport from the PE2-Pt to Py-Pt units in the polychromophores. The energy transfer efficiency is >90% for copolymers that contain 5% of the Py-Pt acceptor units. Time-resolved phosphorescence measurements combined with Monte Carlo exciton dynamics simulations suggest that the mechanism of exciton transport is exchange energy transfer hopping between PE2-Pt units.

The interaction of a series of water-soluble conjugated polyelectrolytes with varying backbone structure, charge type (cationic and anionic), and charge density with a set of seven different proteins is explored by using fluorescence correlation spectroscopy (FCS). The FCS method affords the diffusion time for a particular CPE/protein pair, and this diffusion time is a reflection of the aggregation state of the polymer/protein in the solution. The diffusion time is larger for oppositely charged CPE/protein combinations, reflecting the tendency toward the formation of CPE/protein aggregates in these systems. However, by careful analysis of the data, other factors emerge, including possible effects of hydrophobic interaction in specific CPE/protein systems. The final diffusion time for each CPE/protein mixture varies and the diffusion time response pattern created by the six-CPE array for a typical protein is unique, and this effect was leveraged to develop a sensor array for protein identification by using linear-discriminant analysis (LDA) methods. By application of multimode linear discrimination analysis, the unknown protein samples have been successfully identified with a total accuracy of 93%.Keywords: conjugated polyelectrolyte; fluorescence correlation spectroscopy; protein identification; protein/polymer aggregation;

We report on a sexithienyl and two donor–acceptor−donor oligothiophenes, employing benzothiadiazole and isoindigo as electron-acceptors, each functionalized with a phosphonic acid group for anchoring onto TiO2 substrates as light-harvesting molecules for dye sensitized solar cells (DSSCs). These dyes absorb light to wavelengths as long as 700 nm, as their optical HOMO/LUMO energy gaps are reduced from 2.40 to 1.77 eV with increasing acceptor strength. The oligomers were adsorbed onto mesoporous TiO2 films on fluorine doped tin oxide (FTO)/glass substrates and incorporated into DSSCs, which show AM1.5 power conversion efficiencies (PCEs) ranging between 2.6% and 6.4%. This work demonstrates that the donor–acceptor–donor (D-A-D) molecular structures coupled to phosphonic acid anchoring groups, which have not been used in DSSCs, can lead to high PCEs.Keywords: benzothiadiazole; conjugated oligomer; donor-acceptor chromophore; dye sensitized solar solar cell; isoindigo; phosphonate anchoring group;

A new class of nonaggregating conjugated polyelectrolytes exhibits efficient fluorescence in aqueous solution. Analysis by optical spectroscopy and transmission electron microscopy reveals a unique structure–property correlation between oxygen substitution and aggregation.

In order to understand the photophysics and non-linear optical properties of carbazole containing π-conjugated oligomers of the type ET-Cbz-TE (E = ethynylene, T = 2,5-thienylene, Cbz = 3,6-carbazole), a detailed investigation was carried out on a series of oligomers that feature Au(I) or Pt(II) acetylide “end groups”, as well as a Pt(II)-acetylide linked polymer (CBZ-Au-1 and CBZ-Pt-1, CBZ-Poly-Pt). These organometallic chromophores were characterized by UV-visible absorption and variable temperature photoluminescence spectroscopy, nanosecond transient absorption spectroscopy, open aperture nanosecond z-scan and two photon absorption (2PA) spectroscopy. The Au(I) and Pt(II) oligomers and polymer exhibit weak fluorescence in fluid solution at room temperature. Efficient phosphorescence is observed from the Pt(II) systems below 150 K in a solvent glass; however, the Au(I) oligomer exhibits only weak phosphorescence at 77 K. Taken together, the emission results indicate that the intersystem crossing efficiency for the Pt(II) chromophores is greater than for the Au(I) oligomer. Nonetheless, nanosecond transient absorption indicates that direct excitation affords moderately long-lived triplet states for all of the chromophores. Open aperture z-scan measurement shows effective optical attenuation can be achieved by using these materials. The 2PA cross section in the degenerate S0→S1 transition region was in the range 10–100 GM, and increased monotonically toward shorter wavelengths, reaching 800–1000 GM at 550 nm.

A series of trans-N-heterocyclic carbene (NHC) platinum(II) acetylide complexes of the form (ICy)2Pt(R)2 (where ICy = 1,3-bis-(cyclohexyl)imidazol-2-ylidene and R = 1-Ethynyl-4-(phenylethynyl)benzene (PE2), 2-(9,9-Diethyl-9H-fluoren-7-yl)benzo[d]thiazole (BTF), and 9,9-Diethyl-7-ethynyl-N,N-diphenyl-9H-fluoren-2-amine (DPAF), 2a–c respectively), were synthesized via Hagihara reaction of the unprotected aryl-acetylide ligands with trans-(ICy)2PtCl2 (1) in 47–73% yield. Precursor 1 was generated in a one-pot synthesis via formation of a silver carbene precursor followed by transmetallation, and was obtained in high yield (95%). The single-crystal X-ray structures of 1, 2a–c were determined and analyzed. The photophysical properties of 2a–c were compared to their respective tributyl phosphine (PBu3) analogues. The optical properties of the series were studied by UV-Vis spectroscopy, photoluminescence spectroscopy, nanosecond transient absorption spectroscopy, and open aperture nanosecond z-scan. Coupling of the organic chromophores to the platinum center affords efficient intersystem crossing as concluded by the complexes’ low fluorescence quantum yields, efficient phosphorescence and intense T1 − Tn absorption. Open aperture z-scan with 606 nm, 10 ns laser pulses showed comparable optical attenuation relative to a standard sample of (PBu3)2Pt(DPAF)2 (3c). Pulse limiting was achieved via a dual-mechanism of two-photon absorption (2PA) coupled with excited-state absorption (ESA). TD-DFT Computations were also employed for 2a–c to give greater insight into the nature of the singlet-singlet electronic transitions.

Two cationic poly(phenylene ethynylene) conjugated polyelectrolytes (CPEs) featuring guanidinium side groups were the subject of investigation. Two polymers were examined, one is an alternating co-polymer (P1) in which the guanidinium groups are on every other repeat unit and the second is a homopolymer with the guanidinium groups on every repeat unit. The photophysical properties of the CPEs were investigated in CH3OH and H2O solution by absorption, steady-state fluorescence and fluorescence lifetime spectroscopy. The results indicate that P1 and P2 are molecularly dissolved in CH3OH solution; however, in water the polymers aggregate as evidenced by a substantial reduction in the fluorescence yield. Addition of the non-ionic surfactant (Triton X-100) into the weakly fluorescent aqueous solution of P1 increased the fluorescence by forming a polymer/surfactant complex. The fluorescence of the polymer/surfactant complex in aqueous solution was effectively quenched by the addition of pyrophosphate (PPi) with Stern–Volmer quenching constants (Ksv) ∼ 1.7 × 105 M−1; the quenching occurs because PPi binds to the guanidinium groups and induces the aggregation of the polymer/surfactant complex. In addition, by using fluorescence correlation spectroscopy it was found that the diffusion time of the aggregated complex is increased 9-fold in comparison with the free CPE/surfactant complex. A sensor is developed utilizing the significant changes in fluorescence induced by the addition of PPi.

Controlling charge transfer (CT), charge separation (CS), and charge recombination (CR) at the donor–acceptor interface is extremely important to optimize the conversion efficiency in solar cell devices. In general, ultrafast CT and slow CR are desirable for optimal device performance. In this Letter, the ultrafast excited-state CT between platinum oligomer (DPP-Pt(acac)) as a new electron donor and porphyrin as an electron acceptor is monitored for the first time using femtosecond (fs) transient absorption (TA) spectroscopy with broad-band capability and 120 fs temporal resolution. Turning the CT on/off has been shown to be possible either by switching from an organometallic oligomer to a metal-free oligomer or by controlling the charge density on the nitrogen atom of the porphyrin meso unit. Our time-resolved data show that the CT and CS between DPP-Pt(acac) and cationic porphyrin are ultrafast (approximately 1.5 ps), and the CR is slow (ns time scale), as inferred from the formation and the decay of the cationic and anionic species. We also found that the metallic center in the DPP-Pt(acac) oligomer and the positive charge on the porphyrin are the keys to switching on/off the ultrafast CT process.Keywords: cationic porphyrin; femtosecond transient absorption spectroscopy; platinum oligomer; ultrafast charge transfer;

A time-resolved photoluminescence quenching approach is developed for determining the triplet exciton diffusion coefficient and diffusion length (D and LD, respectively) of phosphorescent conjugated polymers. This method is applied to a solid-state organometallic conjugated polymer with the structure [−Pt(PBu3)2–CC–C6H4–CC−]n (where Bu = n-butyl and −C6H4– is 1,4-phenylene). The approach relies on analysis of the lifetime quenching of the polymer’s phosphorescence by a series of three different quenchers that are dispersed into the polymer phase at varying concentration. The lifetime quenching data are analyzed by using a modified Stern–Volmer quenching expression to determine the diffusion-controlled quenching rate constant, kq, which is then related to the exciton diffusivity, D, and diffusion length, LD. The diffusion coefficients that are determined using the three quenchers are consistent, D ≈ 4 × 10–6 cm2 s–1, and combined with the triplet exciton lifetime of the pristine polymer (τ = 1.05 μs) give an exciton diffusion length LD ≈ 22 nm. The results are compared to literature studies of singlet exciton diffusion in conjugated polymers and triplet exciton diffusion in molecular materials.

This paper describes the photophysical and photoelectrochemical characterization of a light harvesting polychromophore array featuring a polyfluorene backbone with covalently attached Ru(II) polypyridyl complexes (PF-Ru-A), adsorbed on the surface of mesostructured TiO2 (PF-Ru-A//TiO2). The surface adsorbed polymer is characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, providing evidence for the morphology of the surface adsorbed polymer and the mode of binding. Photoexcitation of the Ru(II) complexes bound to the metal oxide surface (proximal) results in electron injection into the conduction band of TiO2, which is then followed by ultrafast hole transfer to the polymer to form oxidized polyfluorene (PF+). More interestingly, chromophores that are not directly bound to the TiO2 interface (distal) that are excited participate in site-to-site energy transfer processes that transport the excited state to surface bound chromophores where charge injection occurs, underscoring the antenna-like nature of the polymer assembly. The charge separated state is long-lived and persists for >100 μs, a consequence of the increased separation between the hole and injected electron.

Energy transfer along a nonconjugated polymer chain is studied with a polystyrene-based copolymer of oligo(phenylene-ethynylene) (OPE) donor and thiophene-benzothiadiazole (TBT) acceptor pendants. The graft copolymers are prepared from reversible addition–fragmentation transfer polymerization (RAFT) and copper(I)-catalyzed azide–alkyne “click” reaction. The singlet energy transfer from donor to accept is studied via fluorescence emission and ultrafast transient absorption spectroscopy. Near unity quenching of the OPE excited state by the TBT moiety occurs on multiple time scales (2–50 ps) dependent on where the initial exciton is formed on the polymer.

A series of platinum tetrayne oligomers, all-trans-Cl–Pt(P2)–[(C≡C)4–Pt(P2)]n–Cl, where P = tri(p-tolyl)phosphine and n = 1–3, was subjected to a detailed photophysical investigation. The photoluminescence of each oligomer at low temperature (T < 140 K) in a 2-methyltetrahydrofuran (Me-THF) glass features an intense and narrow 0–0 phosphorescence band accompanied by a vibronic progression of sub-bands separated by ca. 2100 cm–1. The emission arises from a 3π,π* triplet state concentrated on the (C≡C)4 carbon chain and the vibronic progression originates from coupling of the excitation to the ν(C≡C) stretch. All of the experimental data including ambient temperature absorption, low-temperature photoluminescence, and ambient temperature transient absorption spectroscopy provide clear evidence that the triplet state is localized on a chromophore consisting of approximately two −[(C≡C)4–Pt(P2)]– repeat units. Density functional theory calculations support the hypothesis that the triplet–triplet absorption arises from transitions that are delocalized over two repeat units.

A pair of diketopyrrolopyrrole (DPP) chromophores that are end-functionalized with platinum containing “auxochromes” were subjected to electrochemical and photophysical study. The chromophores contain either platinum acetylide or ortho-metalated 2-thienylpyridinyl(platinum) end-groups (DPP–Pt(CC) and DPP–Pt(acac), respectively). The ground state redox potentials of the chromophores were determined by solution electrochemistry, and the HOMO and LUMO levels were estimated. The chromophores’ photophysical properties were characterized by absorption, photoluminescence, and time-resolved absorption spectroscopy on time scales from sub-picoseconds to microseconds. Density functional theory (DFT) computations were performed to understand the molecular orbitals involved in both the singlet and triplet excited state photophysics. The results reveal that in both platinum DPP derivatives the organometallic auxochromes have a significant effect on the chromophores’ photophysics. The most profound effect is a reduction in the fluorescence yields accompanied by enhanced triplet yields due to spin–orbit coupling induced by the metal centers. The effects are most pronounced in DPP–Pt(acac), indicating that the orthometalated platinum auxochrome is able to induce spin–orbital coupling to a greater extent compared to the platinum acetylide units.

We report three platinum acetylide acrylate monomers containing known two-photon absorption (TPA) chromophores and their covalent incorporation into polymers via free radical polymerization with methyl methacrylate. The photophysical properties of the platinum acetylide monomers and resulting poly(methyl methacrylate) (PMMA) copolymers were investigated to determine if the one- and two-photon photophysical properties of the chromophores were maintained in the copolymers. The photophysical properties of the series of copolymers were studied in solution and solid state with minimum shifts exhibited in the ground state absorption, photoluminescence, and triplet–triplet transient absorption spectra. The polymer films displayed markedly stronger phosphorescence and longer triplet excited state lifetimes than the polymers in solution or the monomers. The incorporation of the platinum acetylide chromophores into the PMMA copolymers allows the materials to be cast as thin films or into free-standing monoliths. Films with ∼3.6 μm in thickness and monoliths with 1 mm path length were fabricated and examined. The nonlinear absorption responses of the polymers in solution were measured via the nanosecond z-scan method, and the solid state polymer monoliths were measured via nonlinear transmittance. Both measurements indicate that the polymers exhibited strong transmittance attenuation at input pulse energies exceeding 100 μJ.Keywords: nonlinear absorption; platinum acetylide; PMMA; polymer; z-scan;

The photophysical properties of three cationic π-conjugated oligomers were correlated with their visible light activated biocidal activity vs S. aureus. The oligomers contain three arylene units (terthiophene, 4a; thiophene-benzotriazole-thiophene, 4b; thiophene-benzothiadiazole-thiophene, 4c) capped on each end by cationic −(CH2)3NMe3+ groups. The oligomers absorb in the visible region due to their donor–acceptor–donor electronic structure. Oligomers 4a and 4b have high intersystem crossing and singlet oxygen sensitization efficiency, but 4c has a very low intersystem crossing efficiency and it does not sensitize singlet oxygen. The biocidal activity of the oligomers under visible light varies in the order 4a > 4b ≈ 4c.Keywords: conjugated oligomer; donor−acceptor; light activated biocide; singlet oxygen;

The phosphorescent metalloporphyrin sensitizer PtTPTNP (TPTNP = tetraphenyltetranaphtho[2,3]porphyrin) has been successfully coupled with perylenediimide (PDI) or rubrene utilized as triplet acceptors/annihilators to upconvert 690 nm incident photons into yellow fluorescence through sensitized triplet–triplet annihilation at overall efficiencies in the 6–7% range while exhibiting exceptional photostability.

We report the photophysics and fluorescence quenching of a series of monodisperse, anionic π-conjugated oligomers that are molecularly dissolved in aqueous solution. These structurally well-defined oligomers feature oligo(phenylene ethynylene) backbones with two −CH2COO– units on each repeat unit, with overall lengths of 5, 7, and 9 repeats. The ionic oligomers display a structured fluorescence band with high quantum efficiency in water, in contrast to the low fluorescence quantum efficiency and pronounced aggregation displayed by structurally similar oligomeric and polymeric (phenylene ethynylene) conjugated polyelectrolytes studied previously. Stern–Volmer (SV) fluorescence quenching studies using cationic charge- and energy-transfer quenchers reveal that all of the oligomers give rise to SV quenching constants (KSV) in excess of 106 M–1, with values increasing with oligomer length, consistent with the amplified quenching effect. The amplified quenching effect is proposed to occur due to the formation of comparatively small oligomer aggregates.Keywords: aggregation; amplified quenching; conjugated oligomer; fluorescence; fluorescence correlation spectroscopy;

We describe a systematic study of triplet sensitization in a poly(phenyleneethynylene) conjugated polyelectrolyte (CPE) in methanol solution by using a series of three cationic iridium complexes with varying triplet energy. The cationic iridium complexes bind to the anionic CPE by ion-pairing, leading to singlet state quenching of the polymer, and allowing for efficient back-transfer of triplet excitation energy to the polymer. Efficient (amplified quenching) of the polymer’s fluorescence is observed for each iridium complex, with Stern–Volmer quenching constants in excess of 105 M–1. Triplet sensitization is confirmed for two of the iridium complexes by monitoring the relative yield of the CPE triplet state by transient absorption spectroscopy. One of the iridium complexes does not sensitize the CPE triplet, and consideration of the energies of the three complexes allows us to bracket the triplet energy of the CPE within the range 1.95–2.26 eV.

Fluorescence correlation spectroscopy (FCS) is applied to investigate aggregation behavior of an anionic conjugated polyelectrolyte (CPE) featuring branched carboxylate groups (PPE-dCO2) upon the addition of different metal ions. FCS results reveal that monovalent metal ions (Na+, K+) bind to the CPE chain but do not induce aggregation, and divalent metal ions (Ca2+, Cu2+) bind and induce the formation of small aggregates. Iron cations (Fe2+ and Fe3+) bind strongly and induce the formation of large CPE aggregates. This is believed to be because of the propensity of these metals to bind to six ligands and thus bridge two of the triacid units on adjacent PPE-dCO2 chains. A comparison between the Stern–Volmer (SV) fluorescence quenching and the relative diffusion time change from FCS demonstrates that the most efficient SV quenching is observed for the ions that give rise to large increases in FCS diffusion time, underscoring the importance of ion-induced aggregation in the amplified quenching effect.

We report on the comparison of the electronic and photophysical properties of a series of related donor–acceptor–donor oligomers incorporating the previously known 2H-benzo[d][1,2,3]triazole (BTz) moiety as the acceptor and the recently reported BTzTD acceptor, a hybrid of BTz and 2,1,3-benzothiadiazole (BTD). Although often implied in the polymer literature that BTz has good acceptor character, we show that this moiety is best described as a weak acceptor. We present electrochemical, computational, and photophysical evidence supporting our assertion that BTzTD is a strong electron acceptor while maintaining the alkylation ability of the BTz moiety. Our results show that the identity of the central atom (N or S) in the benzo-fused heterocyclic ring plays an important role in both the electron-accepting and the electron-donating ability of acceptor moieties with sulfur imparting a greater electron-accepting ability and nitrogen affording greater electron-donating character. We report on the X-ray crystal structure of a BTzTD trimer, which exhibits greater local aromatic character in the region of the triazole ring and contains an electron-deficient sulfur that imparts strong electron-accepting ability. Additionally, we examine the transient absorption spectra of BTzTD and BTz oligomers and report that the BTz core promotes efficient intersystem crossing to the triplet state, while the presence of the thiadiazole moiety in BTzTD leads to a negligible triplet yield. Additionally, while BTz does not function as a good acceptor, oligomers containing this moiety do function as excellent sensitizers for the generation of singlet oxygen.

The linear and nonlinear optical properties of a series of linear and cross-conjugated platinum(II) acetylide complexes that contain extended p-(phenylene vinylene) chromophores are reported. The complexes exhibit very high femtosecond two-photon absorption (2PA) cross section values (σ2 up to 10 000 GM), as measured by nonlinear transmission (NLT) and two-photon excited fluorescence (2PEF) methods. The large 2PA cross sections span a broad range of wavelengths, 570–810 nm, and they overlap with the triplet excited state absorption. Spectral coincidence of high cross section 2PA and triplet absorption is a key feature giving rise to efficient dual-mode optical power limiting (OPL).

Three linear asymmetrically functionalized conjugated molecules composed of five or six aromatic rings were synthesized, bearing a terminal phosphonic acid group, with the objective of enabling their grafting onto inorganic CdSe nanocrystals. These chromophores—oligo(phenylene ethynylenes), oligothiophenes, or donor–acceptor–donor oligothiophenes with a benzothiadiazole acceptor—were designed with decreasing HOMO–LUMO energy gaps such that increasing amounts of light could be absorbed toward the longer wavelengths up to 600 nm. Electrochemical measurements show that the energy offsets between the HOMO and LUMO energies of the organic molecules and the energy bands of the CdSe nanocrystals are well-suited for charge transfer between the organic and inorganic components. The characteristics of each component’s excited state are studied by fluorescence spectroscopy and the interaction between the conjugated molecules and the CdSe nanocrystals in dilute solutions is monitored by photoluminescence quenching. In the latter experiments, where ester and acid derivatives are compared, the pronounced difference in luminescence quenching supports the ability of the phosphonic acid groups to strongly anchor onto the surface of the nanocrystals. Moreover, these results suggest that charge transfer likely occurs between the organic and the inorganic compounds, and appropriate ratios for the corresponding organic/inorganic hybrids preparation are identified. The preparation by direct ligand exchange and the photophysical properties of the hybrids are described, and spectroscopic analysis estimates that the nanocrystals are covered, on average, with 100–200 electroactive organic molecules. The incident photon-to-electron conversion efficiency reflects the solution absorption of the hybrids because it shows the response from both organic and inorganic components.Keywords: conjugated oligomers; donor−acceptor; hybrid materials; nanocrystals; phosphonic acid;

Polystyrene-based polymers that feature pendant Ru(II) polypyridine chromophores have been prepared by using reversible addition–fragmentation chain transfer (RAFT) polymerization combined with the azide–alkyne click reaction. RAFT polymerization was effected using 4-chloromethylstyrene to afford functional polymers with Mn values of 3300 and 8600 g/mol with low polydispersity. Reaction of the resulting poly(4-chloromethylstyrene)s with azide ion afforded the corresponding poly(4-azidomethylstyrene)s, which were further reacted in an azide–alkyne click reaction with (5-ethynyl-1,10-phenanthroline)-bis(2,2-bipyridine)ruthenium(II) to afford the chromophore loaded polymers. The reactions were followed by using nuclear magnetic resonance and infrared spectroscopy, and the results suggest that the click reactions lead to nearly quantitative functionalization of the azidomethyl functional polymers. The photophysical and electrochemical properties of the Ru functional polymers were characterized in solution. Emission quantum yield and lifetime studies reveal that the metal-to-ligand charge transfer excited state is quenched in the polymers relative to a model Ru complex chromophore. This finding indicates that the thiol end-group on the polymers that arises from the thiocarbonylthio RAFT chain transfer agent is able to quench the MLCT state, presumably by a charge transfer mechanism. Stern–Volmer quenching studies show that the polymers are quenched with very high efficiency by negatively charged ions compared to model systems, revealing amplified quenching takes place.

Conjugated polyelectrolyte dendrimers (CPDs) are monodisperse macromolecules that feature a fully π-conjugated dendrimer core surrounded on the periphery by ionic solubilizing groups. CPDs are soluble in water and polar organic solvents, and they exhibit photophysics characteristic of the π-conjugated chromophores comprising the dendrimer core. Here we describe the synthesis and photophysical characterization of series of three generations of CPDs based on a phenylene ethynylene repeat unit structure that is surrounded by an array of anionic sodium carboxylate groups. Molecular dynamics simulations indicate that the first-generation CPD is flat while the second- and third-generation CPDs adopt oblate structures. Photophysical studies, including absorption, fluorescence spectroscopy, and lifetimes, show that the ester protected precursor dendrimers exhibit highly efficient blue fluorescence in THF solution emanating from the phenylene ethynylene chromophore that is in the dendrimer core. By contrast, the water-soluble CPDs have much lower fluorescence quantum yields and the absorption and fluorescence spectra exhibit features of strong chromophore–chromophore interactions. The results are interpreted as suggesting that the CPDs exist as dimer or multimer aggregates, even in very dilute solution. Fluorescence quenching of the anionic CPDs with the dication electron acceptor N,N′-dimethylviologen (MV2+) is very efficient, with Stern–Volmer quenching constants (KSV) increasing with generation number. The third-generation CPD exhibits highly efficient amplified quenching, with KSV ∼ 5 × 106 M–1.

Cationic end-only-functionalized oligo(arylene-ethynylene)s (EO-OPEs) have recently been found to be broad-spectrum and effective antimicrobial agents because of their unique structure and optical properties. In this study, we investigated their potential use for preventing and reducing Escherichia coli (E. coli) biofilms. The Calgary biofilm device (CBD) was used to form bacterial biofilms of E. coli; in these studies, the minimum inhibitory concentration (MIC) and the minimum biofilm eradication concentration (MBEC) were determined. E. coli biofilms uniformly grow on pegs of the CBD device lid. The MIC values determined for EO-OPEs are comparable to those found for standard antibiotics such as kanamycin (MIC = 11.2 μg/mL). About 10–30 times the concentration of EO-OPEs was required to eradicate E. coli biofilms and prevent regrowth in the dark. Near-UV irradiation of EO-OPEs enhanced their efficacy in killing biofilms.

Fluorescence correlation spectroscopy (FCS) is applied to demonstrate avidin-induced cross-linking in a system consisting of a helical anionic conjugated polyelectrolyte (P1) and a biotin-tetramethylrhodamine (TMR) conjugate (2). In a previous study, we used fluorescence spectroscopy to demonstrate that 2 binds to P1 via intercalation of the TMR chromophore into the P1 helix. Addition of avidin to the P1/2 complex induces little change in the fluorescence of the system; however, FCS reveals a remarkable increase in the diffusion time of the P1/2 complex in the presence of avidin. This change is attributed to supramolecular polymer aggregates produced by cross-link formation between the biotin unit of intercalated 2 and avidin. Atomic force microscopy imaging provides evidence supporting the existence of these aggregates. The highly sensitive FCS method is used to develop a novel sensor for the biotin–avidin interaction, with a detection limit of <100 pM for avidin.Keywords: aggregation; avidin−biotin; conjugated polyelectrolyte; fluorescence correlation spectroscopy;

We report the “light switch” effect of [Ru(bpy)2(dppz)]2+ (where bpy = 2,2′-bipyridine and dppz = dipyrido[3,2-a:2′,3′-c] phenazine, Ru-dppz) in the presence of anionic conjugated polyelectrolyte dendrimers (CPDs). The metal-to-ligand charge-transfer luminescence from Ru-dppz is efficient in the presence of CPD because the complex is shielded from water by binding to the hydrophobic dendrimer core.Keywords: amplified quenching; conjugated polyelectrolyte; dendrimer; ruthenium dipyrido[3,2-a:2′,3′-c]phenazine;

One important aspect of p-phenylene-ethynylenes that has not yet been explored is the possible photochemical reactions that can take place in different chemical environments. This is especially important when considering the possible breakdown of these compounds in applications that involve exposure to light, air, and water. In this Letter, a study of the photochemical reaction processes of a cationic oligomer based on the p-phenylene-ethynylene repeat unit is performed in aqueous solution in both the presence and absence of oxygen. Clearly different reaction pathways were observed in the presence and absence of oxygen in aqueous solution. The results of this study revealed the photoaddition of water across the triple bond of the ethynyl group in the absence of oxygen, the addition of singlet-oxygen across the triple-bond in the presence of oxygen, and the cleavage of the alkoxy side chains leaving phenols in both cases.Keywords: antimicrobial polymers; cationic side chains; oligo-phenylene-ethynylene; OPE; organic light-emitting diodes; phenyl ether cleavage; phenylacetylene; photoreaction in water;

A set of two donor−acceptor type conjugated polymers with carboxylic acid side groups have been synthesized and utilized as active materials for dye-sensitized solar cells (DSSCs). The polymers feature a π-conjugated backbone consisting of an electron-poor 2,1,3-benzothiadiazole (BTD, acceptor) unit, alternating with either a thiophene−fluorene−thiophene triad (2a) or a terthiophene (3a) segment as the donor. The donor−acceptor polymers absorb broadly throughout the visible region, with terthiophene−BTD polymer 3a exhibiting an absorption onset at approximately 625 nm corresponding to a ∼1.9 eV bandgap. The polymers adsorb onto the surface of nanostructured TiO2 due to interaction of the polar carboxylic acid units with the metal oxide surface. The resulting films absorb visible light strongly, and their spectra approximately mirror the polymers' solution absorption. Interestingly, a series of samples of 3a with different molecular weight (Mn) adsorb to TiO2 to an extent that varies inversely with Mn. DSSCs that utilize the donor−acceptor polymers as sensitizers were tested using an I−/I3− electrolyte. Importantly, for the set of polymer sensitizers 3a with varying Mn, the DSSC efficiency varies inversely with Mn, a result that reflects the difference in adsorption efficiency observed in the film absorption experiments. The best DSSC cell tested is based on a sample of 3a with Mn ∼ 4000, and it exhibits a ∼65% peak IPCE with Jsc ∼12.6 mA cm−2 under AM1.5 illumination and an overall power conversion efficiency of ∼3%.

The dynamics of negative polaron and triplet exciton transport within a series of monodisperse platinum (Pt) acetylide oligomers is reported. The oligomers consist of Pt–acetylide repeats, [PtL2–C≡C–Ph–C≡C−]n (where L = PBu3 and Ph = 1,4-phenylene, n = 2, 3, 6, and 10), capped with naphthalene diimide (NDI) end groups. The Pt–acetylide segments are electro- and photoactive, and they serve as conduits for transport of electrons (negative polaron) and triplet excitons. The NDI end groups are relatively strong acceptors, serving as traps for the carriers. Negative polaron transport is studied by using pulse radiolysis/transient absorption at the Brookhaven National Laboratory Laser-Electron Accelerator Facility (LEAF). Electrons are rapidly attached to the oligomers, with some fraction initially residing upon the Pt–acetylide chains. The dynamics of transport are resolved by monitoring the spectral changes associated with transfer of electrons from the chain to the NDI end group. Triplet exciton transport is studied by femtosecond–picosecond transient absorption spectroscopy. Near-UV excitation leads to rapid production of triplet excitons localized on the Pt–acetylide chains. The excitons transport to the chain ends, where they are annihilated by charge separation with the NDI end group. The dynamics of triplet transport are resolved by transient absorption spectroscopy, taking advantage of the changes in spectra associated with decay of the triplet exciton and rise of the charge-separated state. The results indicate that negative polarons and excitons are transported rapidly, on average moving distances of ∼3 nm in less than 200 ps. Analysis of the dynamics suggests diffusive transport by a site-to-site hopping mechanism with hopping times of ∼27 ps for triplets and <10 ps for electrons.

A family of π-extended platinum(II) porphyrins has been synthesized and incorporated into solution processed polymer light emitting diodes (PLEDs) and vapor deposited multilayer organic light emitting diodes (OLEDs), giving rise to devices with peak emission ranging from 771 to 1005 nm. The longest wavelength emitter, platinum(II)-5,10,15,20-(3,5-di-tert-butylphenyl)tetraanthroporphyrin (Pt-Ar4TAP), shows an emission maximum at 1005 nm, an external quantum efficiency (EQE) of 0.12%, and a maximum radiant emittance (Rmax) of 0.23 mW/cm2 in single layer PLED architectures, which is enhanced to an EQE of 0.20% with an Rmax of 0.57 mW/cm2 upon vapor deposition of an electron transport layer. In an effort to understand substituent effects and enhance the performance of π-extended Pt-porphyrins in PLEDs and OLEDs, a family of Pt-tetrabenzoporphyrins (Pt-TBPs) with varying functionality was investigated. The luminescent lifetimes of the Pt-TBPs in solution and in films were measured, and a strong correlation was demonstrated between the film lifetimes and the PLED and OLED efficiencies. An improvement in external quantum efficiency (EQE) from 2.07 to 2.49% for PLEDs and from 8.0 to 9.2% for OLEDs was observed between the less substituted Pt-tetraphenyltetrabenzoporphyrin and the more substituted Pt-5,10,15,20-(3,5-di-tert-butylphenyl)tetrabenzoporphyrin. The PLED EQEs were further enhanced to 3.02% with the disubstituted Pt-5,15-(3,5-di-tert-butylphenyl)tetrabenzoporphyrin; however, this increase was not observed for the OLEDs where an EQE of 7.8% was measured.Keywords: electroluminescence; near-infrared; organic light emitting diode; platinum(II) porphyrin;

A comprehensive photophysical study is reported on a family of π-extended platinum(II) porphyrin complexes. The platinum(II) complexes are synthesized from the corresponding free base porphyrins by treatment with platinum(II) acetate in hot benzonitrile, affording the complexes in considerably higher yield than by reaction with platinum(II) chloride. A quantitative study of the absorption and luminescence properties of the metalloporphyrins is presented. A series including tetraarylbenzo-, tetraarylnaphtho-, and tetraarylanthroporphyrin exhibits efficient phosphorescence at 773, 890, and 1020 nm in the near-infrared region, with quantum yields of 0.35, 0.15, and 0.08, respectively. The triplet lifetimes and phosphorescence yields decrease with increasing emission wavelength, consistent with energy gap law behavior. A set of six Pt-tetrabenzoporphyrins (TBPs) with different meso-substituents were examined. The Pt-TBPs exhibit efficient phosphorescence with λmax ∼ 770 nm and with a quantum yield ranging from 0.26–0.49, depending on the substitution pattern. The results show that the 5,15-diarylbenzoporphyrins feature 50–60% higher phosphorescence emission yield compared to the 5,10,15,20-tetraarylbenzoporphyrins. The highest phosphorescence quantum efficiency is observed for a platinum(II) 5,15-diarylbenzoporphyin which emits at 770 nm with a quantum yield of 49%.Keywords: benzoporphyrin; near-infrared; phosphorescence; platinum porphyrin; π-conjugated;

We demonstrate herein a method for chemically modifying cotton fibers and cotton-containing fabric with a light-activated, cationic phenylene–ethynylene (PPE-DABCO) conjugated polyelectrolyte biocide. When challenged with Pseudomonas aeruginosa and Bacillus atropheaus vegetative cells from liquid suspension, light-activated PPE-DABCO effects 1.2 and 8 log, respectively, losses in viability of the exposed bacteria. These results suggest that conjugated polyelectrolytes retain their activity when grafted to fabrics, showing promise for use in settings where antimicrobial textiles are needed.Keywords: Bacillus atrophaeus; biocidal fibers; light activation; poly(phenylene−ethynylene) conjugated polyelectrolytes; Pseudomonas aeruginosa; XTT;

This Spotlight on Applications provides an overview of a research program that has focused on the development and mechanistic study of cationic conjugated polyelectrolytes (CPEs) that function as light- and dark-active biocidal agents. Investigation has centered on poly-(phenylene ethynylene) (PPE) type conjugated polymers that are functionalized with cationic quaternary ammonium solubilizing groups. These polymers are found to interact strongly with Gram-positive and Gram-negative bacteria, and upon illumination with near-UV and visible light act to rapidly kill the bacteria. Mechanistic studies suggest that the cationic PPE-type polymers efficiently sensitize singlet oxygen (1O2), and this cytotoxic agent is responsible for initiating the sequence of events that lead to light-activated bacterial killing. Specific CPEs also exhibit dark-active antimicrobial activity, and this is believed to arise due to interactions between the cationic/lipophilic polymers and the negatively charged outer membrane characteristic of Gram-negative bacteria. Specific results are shown where a cationic CPE with a degree of polymerization of 49 exhibits pronounced light-activated killing of E. coli when present in the cell suspension at a concentration of 1 μg mL–1.Keywords: amplified quenching; antibacterial; antimicrobial; conjugated polyelectrolytes; light activated biocides; singlet oxygen;

Chromophores and materials that exhibit nonlinear absorption over a broad spectrum and with high temporal dynamic range are of interest for application in materials engineering and biology. Recent work by a number of research groups has led to the development of a new family of organometallic chromophores and materials featuring interesting and useful nonlinear absorption properties. These systems contain the platinum acetylide moiety as a fundamental molecular unit, combined with delocalized, π-conjugated electron systems. These organometallic chromophores provide a unique combination of properties, such as negligible ground state absorption in the visible region, large spin–orbit coupling giving rise to high triplet excited state yield, triplet lifetime in the microsecond domain, high two-photon cross-section in the visible and near-infrared regions, and high triplet–triplet absorption cross-section in the visible and near-infrared region. This Spotlight on Application highlights recent developments in this area, combining background and review on nonlinear absorption in platinum acetylide chromophores and describing significant recent results from our own laboratory.Keywords: nonlinear absorption; platinum acetylide; reverse saturable absorption; two-photon absorption;

A new series of conjugated polyelectrolytes (CPE) consisting of an arylene–ethynylene backbone featuring phenyl (Ph), 2,1,3-benzothiadiazole (BTD), or 4,7-bis(2′-thienyl)-2,1,3-benzothiadiazole (TBT) units have been synthesized and characterized. On each polymer repeat unit the CPEs contain two branched ionic side groups each featuring a “triad” of carboxylate (R-CO2–Na+) or ammonium (R-NH3+Cl–) units, giving the polymers six ionic charges per repeat. The photophysical properties of the series of CPEs were investigated in CH3OH and H2O solution by absorption, steady-state fluorescence, and fluorescence lifetime spectroscopy. The different arylene units in the backbone lead to the variation of the HOMO–LUMO gap across the series. The branched, polyionic side chains suppress aggregation of the polymer chains, even in aqueous solution, leading to higher fluorescence quantum yields relative to similar CPEs with linear side chains. UV–vis absorption spectra show that CPEs with anionic branched side chains (R-bCO2–Na) aggregate at low pH, while retaining the photophysical properties of their organic-soluble precursors at high pH. CPEs having branched cationic side chains (R-bNH3+Cl–) exhibit the opposite response to pH change.

We present a study of Förster resonance energy transfer (FRET) between two emissive conjugated polyelectrolytes (CPEs) in layer-by-layer (LbL) self-assembled films as a means of examining their organization and architecture. The two CPEs are a carboxylic acid functionalized polyfluorene (PFl-CO2) and thienylene linked poly(phenylene ethynylene) (PPE-Th-CO2). The PFl-CO2 presents a maximum emission at 418 nm, while the PPE-Th-CO2 has an absorption λmax centered at 431 nm, in sufficient proximity for effective FRET. Several LbL films have been constructed using varied concentrations of the deposition solutions and identity of the buffer layers separating the two emissive layers, using a system of either weak polyelectrolytes, poly(allylamine hydrochloride) (PAH)/poly(sodium methacrylate) (PMA), or strong polyelectrolytes, poly(diallylammonium chloride) (PDDA)/poly(styrene sulfonate) sodium (PSS). The efficiency of FRET has been monitored using fluorescence spectroscopy. Initially, the fluorescence of the PFl-CO2 (Eg ∼ 3.0 eV), which emits at 420 nm, is quenched by the lower band gap PPE-Th-CO2 (Eg ∼ 2.5 eV). For films using the PAH/PMA system as buffer bilayers and deposited from 1 mM solutions, the PFl-CO2 fluorescence is progressively recovered as the number of intervening buffer bilayers is increased. Ellipsometry measurements indicate that energy transfer between the two emissive layers is efficient to a distance of ca. 7 nm.

Three series of cationic oligo p-phenyleneethynylenes (OPEs) have been synthesized to study their structure−property relationships and gain insights into the transition from molecular to macromolecular properties. The absorbance maxima and molar extinction coefficients in all three sets increase with increasing number of repeat units; however, the increase in λmax between the oligomers having 2 and 3 repeat units is very small, and the oligomer having 3 repeat units shows virtually the same spectra as a p-phenyleneethynylene polymer having 49 repeat units. A computational study of the oligomers using density functional theory calculations indicates that while the simplest oligomers (OPE-1) are fully conjugated, the larger oligomers are nonplanar and the limiting “segment chromophore” may be confined to a near-planar segment extending over three or four phenyl rings. Several of the OPEs self-assemble on anionic “scaffolds”, with pronounced changes in absorption and fluorescence. Both experimental and computational results suggest that the planarization of discrete conjugated segments along the phenylene−ethynylene backbone is predominantly responsible for the photophysical characteristics of the assemblies formed from the larger oligomers. The striking differences in fluorescence between methanol and water are attributed to reversible nucleophilic attack of structured interfacial water on the excited singlet state.

A pair of anionic conjugated polyelectrolytes that contain three-ring (phenylene ethynylene) units linked by a single −CH2– or −O– tether (P1 and P2, respectively) are studied. The linkers serve to interrupt the π conjugation along the polymer backbone. Fluorescence spectroscopy reveals that P2 forms a fluorescent aggregate in methanol and water; however, the fluorescence of P1 is much weaker in water, and P1 exhibits only weak aggregate fluorescence. Fluorescence quenching of the polymers was examined using methyl viologen (MV2+) as a cationic quencher. P1 shows only a weak amplified quenching effect, with a Stern–Volmer quenching constant of KSV ≈ 6 × 105 M–1 in methanol. Interestingly, for P2 in methanol, the aggregate emission is strongly quenched with KSV ≈ 5 × 106 M–1, which is comparable to the highest quenching efficiency observed for fully π-conjugated polyelectrolytes. By contrast, the monomer emission is quenched much less efficiently, with KSV ≈ 2 × 105 M–1. The results are explained by a model in which −O– linked polymer P2 is able to fold into a helical conformation in solution, which facilitates the formation of extended π-stacked aggregates allowing long-distance exciton transport.

Cationic poly(phenylene ethynylene)- (PPE-) based conjugated polyelectrolytes (CPEs) with six different chain lengths ranging in degree of polymerization from ∼7 to ∼49 were synthesized from organic-soluble precursor polymers. The molecular weight of the precursor polymers was controlled by the amount of a monofunctional “end-capping” agent added to the polymerization reaction. Cationic CPEs were prepared by quaternization of amine groups to tetraalkylammonium groups. Their structure–property relationships were investigated by observing their photophysical properties and antibacterial activity. The polymers were found to exhibit a chain-length dependence in their photophysical properties. It has also been observed that the polymers exhibit effective antibacterial activity against both Gram-positive and Gram-negative bacteria under UV irradiation, whereas they show little antibacterial activity in the dark. An effect of chain length on the light-activated antibacterial activity was also found: The shortest polymer (n = 7) exhibited the most effective antibacterial activity against both Gram-positive and Gram-negative bacteria.

A poly(phenylene ethynylene) conjugated polymer (PPE-NMe3+-COO−) containing tetraalkylammonium groups and carboxylate groups has been synthesized by Sonogashira coupling. Due to the presence of the strong cationic and weak anionic pendant units, the polymer undergoes a pH-induced transition from cationic polyelectrolyte to polyampholyte due to deprotonation of the carboxylic acid units in basic solution. Studies of the pH dependence of the polymers’ optical properties reveal changes in absorption oscillator strength and fluorescence quantum efficiency that are triggered by the transition from cationic polyelectrolyte to polyampholyte nature. Stern−Volmer fluorescence quenching of PPE-NMe3+-COO− with a negatively charged quencher 1,4,5,8-naphthalenediimide-N,N-bis(methylsulfonate) (NDS) shows that the polymer fluorescence quenching is amplified at low pH where the polymer is a polycation, whereas the quenching efficiency is considerably less at high pH.

Direct detection of pyrophosphate (PPi) in aqueous solution is demonstrated using a cationic poly(phenylene-ethynylene) with polyamine side chains. Pyrophosphate-induced polymer aggregation causes a significant spectroscopic change, which in turn allows quantification of dissolved PPi using ratiometric signals.

The two-photon excited fluorescence of a conjugated polyelectrolyte (CPE), PPESO3, was studied in methanol and in water. The photophysical and amplified quenching properties of the CPE observed under two-photon excitation were comparable to the results obtained under one-photon excited conditions. Two-photon fluorescence microscopy performed with PPESO3-coated silica nanoparticles in HeLa cells provided images with significantly improved resolution compared to one-photon microscopy, demonstrating the utility of the CPE as a fluorescent probe in two-photon fluorescence cell imaging.Keywords: cell imaging; conjugated polyelectrolytes; near-infrared; two-photon absorption

A biotin-tetramethylrhodamine (biotin-TMR) quencher-ligand interacts with a (phenylene-ethynylene) based helical conjugated polyelectrolyte (poly-1) via intercalation of the TMR unit into the helix. The interaction is signaled by efficient fluorescence resonance energy transfer (FRET) from the polymer to the TMR chromophore. Avidin addition to the poly-1/biotin-TMR intercalation complex does not interrupt FRET, instead resulting in the formation of avidin−biotin “cross-links”. Mixing of biotin-TMR with avidin prior to addition of the polymer efficiently disrupts the FRET signal, giving rise to a sensor with a detection limit of 100 pM for avidin. Study of the FRET response as a function of biotin-TMR and avidin concentration affords insight into the interaction of the protein with the poly-1/biotin-TMR intercalation complex.

A series of platinum-containing organometallic dimer complexes has been synthesized and the photophysical properties have been investigated under one- and two-photon (2PA) absorption conditions. The complexes have the general structure [DPAF−C≡C−Pt(PBu3)2−C≡C−Ar−C≡C−Pt(PBu3)2−C≡C−DPAF], where Ar is a π-conjugated unit, Bu = n-butyl, and DPAF = diphenylamino-2,7-fluorenylene. The core Ar units include 1,4-phenylene, 2,5-thienylene, 5,5′-(2,2′-bithienylene), 2,5-(3,4-ethylenedioxythiophene, 2,1,3-benzothiadiazole, and 4,7-dithien-2-yl-2,1,3-benzothiadiazole. Absorption and photoluminescence spectroscopy indicates that the complexes feature low-lying excited states based on both the core [-Pt(PBu3)2−C≡C−Ar−C≡C−Pt(PBu3)2-] chromophore as well as the DPAF units. Photoexcitation of the complexes produces a singlet state excited state, which rapidly undergos intersystem crossing to afford a triplet state that has a lifetime in the microsecond time domain. In most cases, the lowest energy triplet state is localized on the core chromophore. Femtosecond 2PA spectra are measured along with triplet−triplet absorption spectra and nanosecond intensity-dependent transmission for solutions of the complexes. Each of the complexes features a 2PA absorption band in the near-infrared region (λ ≈ 700−750 nm) with a cross section 50−200 GM that is ascribed to the DPAF chromophore. The complexes also feature broad triplet−triplet absorption throughout the visible and near-infrared regions (λ ≈ 500−800 nm, ϵTT ≈ 5−10 × 104 M−1 cm−1). Each of the complexes exhibits efficient nonlinear absorption of nanosecond pulses in the near-infrared region (600−800 nm), and we demonstrate that effect is most efficient in the chromophores where the 2PA cross section maxima coincides spectrally with the excited triplet state absorption.

The series of three donor-spacer-acceptor complexes, DPAF-Ptn-NDI, has been synthesized and characterized using time-resolved absorption spectroscopy. In these complexes, the donor is a (diphenylamino)-2,7-fluorenylene (DPAF) unit, the acceptor is a naphthalene diimide (NDI), and the spacers are a series of platinum acetylides of varying lengths, [−Pt(PBu3)2—C≡C—Ph—C≡C−]n (where Bu = n-butyl, Ph = 1,4-phenylene and n = 1, 2, and 3). Electrochemistry indicates that the DPAF-Ptn-NDI system has a charge transfer state at ca. 1.5 eV above the ground state that is based on one electron transfer from the DPAF donor to the NDI acceptor. Transient absorption spectroscopy on time scales ranging from 0.2 ps to 1 μs reveals that excitation of all of the complexes leads to production of the charge transfer state with nearly unit quantum efficiency. The rates for charge separation and charge recombination are not strongly dependent upon the length of the platinum acetylide spacer, suggesting that the spacer is actively involved in the electron (hole) transport processes. Analysis of the experimental results leads to a model in which charge separation and charge recombination occur by hole-hopping via states localized on the [−Pt(PBu3)2—C≡C—Ph—C≡C−]n bridge.

Microcapsules consisting of alternating layers of oppositely charged poly(phenylene ethynylene)-type conjugated polyelectrolytes (CPEs) were prepared via layer-by-layer deposition onto MnCO3 template particles followed by dissolution of the template particles using an ethylenediaminetetraacetate solution. The resulting microcapsules exhibit bright-green fluorescence emission characteristics of the CPEs. Strong antimicrobial activity was observed upon mixing of polyelectrolyte capsules with Cobetia marina or Pseudomonas aeruginosa followed by white-light irradiation. It was demonstrated that the materials act as highly effective light-activated micro “Roach Motels” with greater than 95% kill after exposure to ∼1 h of white light.Keywords: biocide; confocal microscopy; conjugated polymer; polyelectrolyte capsule; singlet oxygen

We report on two pairs of platinum acetylide based polymers and model oligomers utilizing a 2,1,3-benzothiadiazole (BTD) acceptor moiety flanked on either side by either 2,5-thienyl donor units (Pt2BTD-Th and p-PtBTD-Th) or (3,4-ethylenedioxy)-2,5-thienyl donors (Pt2BTD-EDOT and p-PtBTD-EDOT). Both oligomer/polymer pairs absorb strongly throughout the visible region; however, because the (ethylenedioxy)thiophene moiety is a stronger donor than thiophene, the latter oligomer/polymer pair has a correspondingly lower band gap and, therefore, harvests light more efficiently at longer wavelengths. p-PtBTD-Th exhibits a relatively narrow molecular weight distribution with a number-average molecular weight (Mn) of 22 kDa, while p-PtBTD-EDOT exhibits a comparable Mn of 33 kDa but has a high polydispersity index likely due to aggregation. We provide a complete report of the photophysical and electrochemical characterization of the two oligomer/polymer pairs. The photophysical studies reveal that the materials undergo relatively efficient intersystem crossing. In a discussion of the energetics of photoinduced electron transfer from the platinum polymers to [6,6]-phenyl C61 butyric acid methyl ester (PCBM), it is noted that while the singlet state is quenched efficiently, the triplet state is not quenched, indicating that charge generation in the photovoltaic materials must ensue from the singlet manifold. Finally, organic photovoltaic devices based on blends of p-PtBDT-Th or p-PtBDT-EDOT with PCBM were characterized under monochromatic and simulated solar (AM1.5) illumination. Optimized devices exhibit an open-circuit voltage (Voc) of ∼0.5 V, a short-circuit current density (Isc) of ∼7.2 mA cm−2, and a fill factor of ∼35%, which yields overall power conversion efficiencies of 1.1−1.4%.Keywords: conjugated polymer; fullerene; organometallic polymer; solar cell; triplet state

A series of poly(arylene ethynylene) conjugated polyelectrolytes (CPEs) substituted with carboxylic acid side groups have been synthesized and characterized. The polymers feature a backbone consisting of a carboxylated dialkoxyphenylene-1,4-ethynylene unit alternating with a second arylene ethynylene moiety of variable electron demand. The HOMO−LUMO gap is varied across the series, giving rise to a set of four polymers that have absorption maxima ranging from 404 to 495 nm. The CPEs adsorb effectively from solution onto nanostructured TiO2 films, giving rise to TiO2/CPE films that absorb ∼90% of the incident light at the absorption band maximum. The photocurrent generation efficiency of the TiO2/CPE films was examined in a solar cell configuration using an I3−/I− propylene carbonate electrolyte and a Pt/fluorine-doped tin oxide counter electrode. Most of the films exhibit good photocurrent generation efficiency with a peak quantum efficiency of ∼50% at wavelengths corresponding to the polymers’ absorption band maximum. Interestingly, the photocurrent generation efficiency for the lowest-band-gap polymer is substantially lower compared to the other three systems. This effect is attributed to efficient nonradiative decay of excitons at trap sites arising from interchain contacts distal from the TiO2/CPE interface.Keywords: band gap; charge transfer; conjugated polyelectrolyte; dye-sensitized solar cell; photocurrent generation; power conversion

The new metalloporphyrin Pt(tptnp), where tptnp = tetraphenyltetranaphtho[2,3]porphyrin, has been prepared and subjected to photophysical and electrooptical device studies. In degassed toluene solution at room temperature Pt(tptnp) features efficient phosphorescence emission with λmax 883 nm with a quantum efficiency of 0.22. The complex has been used as the active phosphor in polymer and organic light-emitting diodes. Polymer light-emitting diodes based on a spin-coated emissive layer consisting of a blend of Pt(tptnp) doped in poly(9-vinylcarbazole) and 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole exhibit near-IR emission with λmax 896 nm, with a maximum external quantum efficiency (EQE) of 0.4% and a maximum radiant emittance of 100 μW/cm2. Organic light-emitting diodes prepared via vapor deposition of all layers and that feature an optimized multilayer hole injection and electron blocking layer heterostructure with an emissive layer consisting of 4,4′-bis(carbazol-9-yl)biphenyl (CBP) doped with Pt(tptnp) exhibit a maximum EQE of 3.8% and a maximum radiant emittance of 1.8 mW/cm2. The polymer and organic light-emitting diodes characterized in this study exhibit record high efficiency for devices that emit in the near-IR at λ >800 nm.Keywords: electrophosphorescence; metalloporphyrin; near-infrared; organic light emitting diodes; polymer light emitting diodes

Addition of adenosine 5′-triphosphate (ATP) to a solution of the anionic conjugated polyelectrolyte PPECO2 and copper(II) ion (Cu2+) recovers the Cu2+-quenched fluorescence of PPECO2 to a significantly greater extent compared with the addition of adenosine 5′-diphosphate (ADP) or adenosine 5′-monophosphate (AMP) at the same concentration levels. Taking advantage of the differential response of the PPECO2−Cu2+ system to ATP, ADP and AMP, we have developed fluorescence turn-off and turn-on assays that monitor the catalytic activity of adenylate kinase (ADK) in the equilibrium transphosphorylation reaction (ATP + AMP ⇔ 2ADP). The fluorescence turn-on and turn-off assays monitor the forward and reverse transphosphorylation reactions, respectively. The forward assay operates with ATP substrate present at the submillimolar concentration range and offers a straightforward and rapid detection of ADK catalytic activity with the enzyme present in the nanomolar range, in either end-point or real-time formats. The real-time fluorescence intensity from PPECO2 can be converted to substrate (ATP) concentration in the forward reaction assay by using an ex-situ calibration curve, allowing ADK catalyzed reaction rates and kinetic parameters to be determined. ADK activation by Mg2+ and inhibition by Ag+ and product are analyzed using the optimized assay system. Non-specific interactions are observed between the assay complex and other proteins, but the signal response to the ADK assay is demonstrated to mainly arise from the specific enzyme catalyzed transphosphorylation reaction.

This perspective seeks to identify an area of soft materials research focused on the study of functional polyelectrolytes. These materials combine the useful properties intrinsic to polyelectrolyte chains, with added functionality provided by specific molecular (or polymeric) functional groups that are present in the polymer backbone or as a pendant functionality. Examples are provided to demonstrate how the combined functionality can be used to create films and assemblies with interesting and useful optical, electro-optical, and electronic properties.

A pair of cationic phenylene ethynylene oligomers (OPEs) have been synthesized, and their optical properties have been studied in solution with and without added scaffold materials, including carboxymethylcellulose, carboxymethylamylose, and Laponite. The OPEs are strongly fluorescent in methanol solution, but in water, the fluorescence yield is suppressed. The addition of scaffolds to aqueous solutions of OPEs leads to a red shift in the absorption and in most cases a significant increase in the fluorescence quantum yield. The effects most likely arise because of template-induced formation of linear J-dimers or possibly because of planarization, which give rise to an effective increase in the conjugation length of OPEs.

Conjugated polyelectrolytes (CPEs) have become one of the most utilized materials in chemo- and bio-sensory systems. Useful properties of CPEs, such as amplified quenching effects and aggregation behavior, are illustrated in detail in order to provide guidelines for underlying concepts of CPE-based sensors. Well established sensing mechanisms, such as conformational changes and fluorescence resonance energy transfer, are reviewed with representative examples. Target species include small ions, small biomolecules, proteins, enzymatic activities, and DNA. New and unique mechanisms for CPE-based sensing are also described.

A platinum acetylide-based polymer (p-Pt2BPyPh) that contains 2,2′-bipyridine units in the polymer backbone has been synthesized. A model complex (Pt2BPyPh2) has also been prepared that features the same structure as a single polymer repeat unit. The polymer and model complex exhibit moderately efficient and long-lived phosphorescence emission from a triplet excited state. The effect of addition of six different transition metal ions (Fe3+, Co2+, Zn2+, Ni2+, Cu2+ and Pd2+) on the absorption and phosphorescence spectra of p-Pt2BPyPh and Pt2BPyPh was examined. The results show that in every case, the metal ions bind to the bipyridine unit in the polymer (model) backbone, and metal ion binding induces a red-shift in the near-UV absorption band. Phosphorescence spectroscopy shows that for all of the metals (with the exception of Zn2+), metal ion binding is accompanied by phosphorescence quenching. For some of the metal ions (Cu2+ and Ni2+) quenching of the polymer is considerably more efficient than in the model, an observation consistent with an “amplified quenching effect” that is analogous to that observed for quenching of fluorescent conjugated polymers. A semi-quantitative analysis of the absorption and phosphorescence data provide a model consistent with the notion that triplet exciton hopping along the polymer chain is rapid compared to the triplet lifetime, and that the overall quenching efficiency for the different metal ions is controlled by the intrinsic rate of triplet quenching within the metal ion–bipyridine complex.

We report the synthesis and structural characterization of a series of monodisperse platinum acetylide oligomers with the general structure NDI-[Ph−C≡C−Pt(PBu3)2−C≡C−]n−Ph−NDI, where n = 2, 3, 6, or 10, Ph = 1,4-phenylene, NDI is a substituted 1,4,5,8-naphthalene diimide, and the geometry at the Pt centers is trans. The oligomers were synthesized via an iterative-convergent approach utilizing organometallic synthons that feature orthogonally protected terminal acetylene units. The 31P NMR spectra of the oligomers are especially revealing as to their structure, due to a difference in chemical shift for the internal and terminal Pt(PBu3)2 units. The oligomers were also characterized by electrochemistry, UV−visible absorption, and photoluminescence spectroscopy. The emission spectroscopy reveals that the triplet exciton is efficiently quenched in the NDI end-capped oligomers, and the quenching is thought to arise due to photoinduced charge separation.

The fluorescence of the anionic, carboxylate-substituted poly(phenylene ethynylene) polymer PPECO2 is quenched very efficiently via the addition of 1 equiv of Cu2+. Addition of pyrophosphate (PPi) into the weakly fluorescent solution of PPECO2 and Cu2+ induces recovery of the polymer’s fluorescence; the recovery occurs because PPi complexes with Cu2+, effectively sequestering the ion so it cannot bind to the carboxylate groups of the polymer. A calibration curve was developed that relates the extent of fluorescence recovery to [PPi], making the PPECO2−Cu2+ system a sensitive and selective turn-on sensor for PPi. Using the PPECO2−Cu2+ system as the signal transducer, a real-time fluorescence turn-off assay for the enzyme alkaline phosphatase (ALP) using PPi as the substrate is developed. The assay operates with [PPi] in the micromolar range, and it offers a straightforward and rapid detection of ALP activity with the enzyme present in the nanomolar concentration range, operating either in an end point or real-time format. Kinetic and product inhibition parameters are derived by converting time-dependent fluorescence intensity into PPi (substrate) concentration, thus allowing calculation of the initial reaction rates (vo). Weak, nonspecific fluorescence responses are observed concomitant to addition of other proteins to the assay solution; however, the signal response to ALP is demonstrated to arise from the ALP catalyzed hydrolysis of PPi to phosphate (Pi).

The series of polyynes with the structure trans,trans-[Ar−Pt(P2)−(C≡C)n−Pt(P2)−Ar], where P = tri(p-tolyl)phosphine, Ar = p-tolyl, and n = 3, 4, 5, 6 (6, 8, 10, 12 sp carbon atoms), has been subjected to a comprehensive photophysical investigation. At low temperature (T < 140 K) in a 2-methyltetrahydrofuran (MTHF) glass, the complexes exhibit moderately efficient phosphorescence appearing as a series of narrow (fwhm < 200 cm−1) vibronic bands separated by ca. 2100 cm−1. The emission is assigned to a 3π,π* triplet state that is concentrated on the sp carbon chain, and the vibronic progression arises from coupling of the excitation to the −C≡C− stretch. The 0−0 energy of the phosphorescence decreases with increasing sp carbon chain length, spanning a range of over 6000 cm−1 across the series. Transient absorption spectroscopy carried out at ambient temperature confirms that the 3π,π* triplet is produced efficiently, and it displays a strongly allowed triplet−triplet absorption. In the MTHF solvent glass (T < 140 K), the emission lifetimes increase with emission energy. Analysis of the triplet nonradiative decay rates reveals a quantitative energy gap law correlation. The nonradiative decay rates can be calculated by using parameters recovered from a single-mode Franck−Condon fit of the emission spectra.

This paper reports the synthesis and photophysical study of a series of anionic, carboxylate-substituted poly(phenylene ethynylene)-based conjugated polyelectrolytes (CPEs) with variable chain lengths. These CPEs are of interest as they allow the study of the effect of chain length on amplified fluorescence quenching. The CPEs were synthesized via organic soluble ester precursor polymers. The degree of polymerization of the precursor polymers was controlled by addition of a monofunctional “end-cap” to the polymerization reaction. The CPEs were obtained postpolymerization by base-promoted hydrolysis of the ester protecting groups. Stern−Volmer fluorescence quenching of the CPEs in methanol with monovalent electron-transfer quenchers (MV+ and HV+) show that the Stern−Volmer quenching constant (KSV) increases with polymer chain length reaching a maximum of ca. 2 × 105 M−1 at a degree of polymerization of 49. The results indicate that a maximum quenching amplification factor of 53 is attained under conditions where monovalent quencher ions interact with nonaggregated (single) polymer chains.

The CuCl-catalyzed reaction of butadiynyl complex trans-(C6F5)(Et3P)2Pt(C≡C)2H (6) and trans-(p-tol)(Et3P)2PtCl (7) in HNEt2 affords trans,trans-(C6F5)(Et3P)2Pt(C≡C)2Pt(PEt3)2(p-tol) (8; 62%), but similar reactions of p-tol3P-substituted coupling partners, or of 6 and trans-(p-tol)(p-tol3P)2PtCl (4), are not successful. However, 6 and 4 react under modified conditions (t-BuOK, KPF6, cat. CuCl, THF/methanol) to give trans,trans-(C6F5)(Et3P)2Pt(C≡C)2Pt(Pp-tol3)2(p-tol) (9; 91%). The hexatriynyl complexes trans-(C6F5)(R3P)2Pt(C≡C)3H (R = p-tol, Et) are treated with 4 and 7, respectively, under the original or modified conditions. Workups give trans,trans-(C6F5)(R3P)2Pt(C≡C)3Pt(PR3)2(p-tol) (R = p-tol, 12, 40−63%; Et, 17, 59%). The reaction of 6 and ClAu(PPh3) and KN(SiMe3)2 affords trans-(C6F5)(Et3P)2Pt(C≡C)2Au(PPh3) (18, 97%). The CuCl-catalyzed reaction of (η5-C5H5)W(CO)3(C≡C)2H and trans-(C6F5)(Et3P)2PtCl in HNEt2 generates trans-(C6F5)(Et3P)2Pt(C≡C)2W(CO)3(η5-C5H5). The crystal structures of 8, 9, 17, and 18, or solvates thereof, are determined and analyzed in detail. The square-planar end-groups in the C4 adducts 8 and 9 define angles of 62.3−34.7°, as opposed to ca. 0° in the C6 adduct 17. Both 9 and 18 exhibit phosphorescence from triplet states concentrated on the C4 segments. Data with 9 in low-temperature glasses suggest two conformers with different end-group−end-group orientations.

A series of water soluble, cationic conjugated polyelectrolytes (CPEs) with backbones based on a poly(phenylene ethynylene) repeat unit structure and tetraakylammonium side groups exhibit a profound light-induced biocidal effect. The present study examines the biocidal activity of the CPEs, correlating this activity with the photophysical properties of the polymers. The photophysical properties of the CPEs are studied in solution, and the results demonstrate that direct excitation produces a triplet excited-state in moderate yield, and the triplet is shown to be effective at sensitizing the production of singlet oxygen. Using the polymers in a format where they are physisorbed or covalently grafted to the surface of colloidal silica particles (5 and 30 μm diameter), we demonstrate that they exhibit light-activated biocidal activity, effectively killing Cobetia marina and Pseudomonas aeruginosa. The light-induced biocidal activity is also correlated with a requirement for oxygen suggesting that interfacial generation of singlet oxygen is the crucial step in the light-induced biocidal activity.

A new fluorescence turn-on sensor consisting of PPE-CO2–/Cu2+ shows high selectivity for pyrophosphate over other anions and is used to develop a real-time assay for alkaline phosphatase.

The fullerene end-capped platinum acetylide donor–acceptor triad Pt2ThC60 was synthesized and characterized by using photophysical methods and photovoltaic device testing. The triad consists of the platinum acetylide oligomer Ph––Pt(PBu3)2––Th––Pt(PBu3)2––Ph (Ph = phenyl and Th = 2,5-thienyl, stereochemistry at both Pt centers is trans) that contains fulleropyrrolidine moieties on each of the terminal phenylene units. Electrochemistry of the triad reveals relatively low potential oxidation and reduction waves corresponding, respectively, to oxidation of the platinum acetylide and reduction of the fulleropyrrolidine units. Photoluminescence spectroscopy shows that the singlet and triplet states of the platinum acetylide chromophore are strongly quenched in the triad assembly, both in solution at ambient temperature as well as in a low-temperature solvent glass. The excited state quenching arises due to intramolecular photoinduced electron transfer to produce a charge separated state based on charge transfer from the platinum acetylide (donor) to the fulleropyrrolidine (acceptor). Picosecond time resolved absorption spectroscopy confirms that the charge transfer state is produced within 1 ps of photoexcitation, and it decays by charge recombination within 400 ps. Organic photovoltaic devices fabricated using spin-coated films of Pt2ThC60 as the active material operate with modest efficiency, exhibiting a short circuit photocurrent of 0.51 mA cm−2 and an open circuit voltage of 0.41 V under 100 mW cm−2/AM1.5 illumination. The results are discussed in terms of the relationship between the mechanism of photoinduced electron transfer in the triad and the comparatively efficient photovoltaic response exhibited by the material.

The quenching behavior of a water-soluble cationic poly (para-phenylene) bearing quaternized ammonium side groups (P-NEt3+) was studied. P-NEt3+ is efficiently quenched by sodium anthraquinone-2,6-disulfonate (AQS) and sodium 1,4,5,8-naphthalenediimide-N,N’-bis (methylsulfonate) (NDS) in aqueous solution via a photo-induced electron-transfer mechanism. Absorption spectra of the NDS/P-NEt3+ ion-pair complex indicated formation of a stable charge-transfer complex in the ground state. A large spectral shift and band broadening occurred during AQS/P-NEt3+ complex formation, which is believed to arise due to P-NEt3+ conformational changes induced by hydrophobic interactions. Finally, a protein sensor that relies on the quenching behavior of P-NEt3+ was designed based on the quencher-tether-ligand (QTL) approach. AQS tethered to biotin (AQS-E-Biotin) was used along with P-NEt3+ to sense avidin.

Relatively efficient photovoltaic devices were fabricated using blends of a phosphorescent platinum–acetylide polymer and a fullerene (PCBM); involvement of the triplet excited state of the platinum–acetylide polymer in photoinduced charge transfer is believed to contribute to the device efficiency.

The photophysical properties of a π-conjugated metal–organic oligomer vary smoothly with solvent composition. The variation is believed to arise from solvent-tuned configuration mixing of 3π,π* and 3MLCT levels.

The luminescence from conjugated polyelectrolytes that contain pendant metal complex units is quenched very efficiently by oppositely charged electron acceptors.

A facile and original synthesis of four 2,2′-bipyridine (bipy) ligands grafted with thiophene subunits is described using phase transfer experimental conditions: related Ru(II) complexes exhibit well-defined redox and photophysical properties which were probed by cyclic voltammetry, UV–vis, steady-state emission and transient absorption spectroscopy.

The fluorescence, absorption and fluorescence quenching properties of an anionic poly(phenylene ethynylene) are investigated in H2O and MeOH solutions.

We report the photophysics of two complexes of the type Ir(ppy)2(OAE)+, where ppy = 2-phenylpyridine and OAE is a π-conjugated oligo(arylene ethynylene) ligand.

There has been a surge of interest concerning the synthesis, optical and electronic properties of π-conjugated polymers that contain transition metal complexes. The integration of transition metal chromophores that feature metal to ligand charge transfer (MLCT) excited states into a π-conjugated polymer permits easy variation of the material’s optical and electronic properties. In this review, we survey a number of recent photophysical studies that examine π-conjugated oligomer or polymer/transition metal complex hybrids. The effects of the types of π-conjugated backbone, oligomer and polymer structure, the conjugation length and coordination to a variety of metal chromophores on the photophysics of the organic-metal hybrids are discussed. The degree of interaction between the polymer (or oligomer) and metal complex based excited states dramatically modulates the observed photophysics.

The pyrophosphate anion (PPi) plays an important role in biochemical processes. Therefore, a simple but reliable analytical technique is essential for selective detection of PPi in biochemical systems. Here, we present a principal component analysis (PCA) method for analytical determination of PPi concentration using a fluorescent conjugated polyelectrolyte (CPE) combined with a polyamine modifier. The CPE has anionic side chains and dissolves molecularly in water, as indicated by its structured fluorescence emission spectrum. However, addition of tris(3-aminoethyl)amine (tetraamine or N4) quenches the CPE fluorescence emission. Tetraamine, which is a polycation at neutral pH, binds multiple anionic CPE chains, leading to aggregate formation, resulting in aggregation-induced fluorescence quenching. Addition of PPi to the polymer–amine aggregate reverses the process, resulting in fluorescence recovery. The relatively higher concentration of PPi compared to that of the polymer allows it to effectively compete to bind the amine, thus releasing molecularly dissolved polymer chains. Fluorescence correlation spectroscopy of the P1/N4 complex and of P1/N4/PPi confirms the change in size of the CPE aggregates that occurs upon reversible aggregation. Application of PCA to the fluorescence emission data set of standard samples yields two principal components, which are used to create a predictive model for PPi analysis. The PCA method is able to directly determine the concentration of PPi with approximately 95% accuracy within the concentration range from 100 μM to 3 mM, without the need for a reference state as is typically needed for ratiometric fluorescence assays.Topics: Chemoinformatics; Fluorescence; Molecular association;

The phosphorescent metalloporphyrin sensitizer PtTPTNP (TPTNP = tetraphenyltetranaphtho[2,3]porphyrin) has been successfully coupled with perylenediimide (PDI) or rubrene utilized as triplet acceptors/annihilators to upconvert 690 nm incident photons into yellow fluorescence through sensitized triplet–triplet annihilation at overall efficiencies in the 6–7% range while exhibiting exceptional photostability.

A new fluorescence turn-on sensor consisting of PPE-CO2–/Cu2+ shows high selectivity for pyrophosphate over other anions and is used to develop a real-time assay for alkaline phosphatase.

The fullerene end-capped platinum acetylide donor–acceptor triad Pt2ThC60 was synthesized and characterized by using photophysical methods and photovoltaic device testing. The triad consists of the platinum acetylide oligomer Ph––Pt(PBu3)2––Th––Pt(PBu3)2––Ph (Ph = phenyl and Th = 2,5-thienyl, stereochemistry at both Pt centers is trans) that contains fulleropyrrolidine moieties on each of the terminal phenylene units. Electrochemistry of the triad reveals relatively low potential oxidation and reduction waves corresponding, respectively, to oxidation of the platinum acetylide and reduction of the fulleropyrrolidine units. Photoluminescence spectroscopy shows that the singlet and triplet states of the platinum acetylide chromophore are strongly quenched in the triad assembly, both in solution at ambient temperature as well as in a low-temperature solvent glass. The excited state quenching arises due to intramolecular photoinduced electron transfer to produce a charge separated state based on charge transfer from the platinum acetylide (donor) to the fulleropyrrolidine (acceptor). Picosecond time resolved absorption spectroscopy confirms that the charge transfer state is produced within 1 ps of photoexcitation, and it decays by charge recombination within 400 ps. Organic photovoltaic devices fabricated using spin-coated films of Pt2ThC60 as the active material operate with modest efficiency, exhibiting a short circuit photocurrent of 0.51 mA cm−2 and an open circuit voltage of 0.41 V under 100 mW cm−2/AM1.5 illumination. The results are discussed in terms of the relationship between the mechanism of photoinduced electron transfer in the triad and the comparatively efficient photovoltaic response exhibited by the material.

A series of variable band-gap donor–acceptor–donor (DAD) chromophores capped with platinum(II) acetylide units has been synthesized and fully characterized by electrochemical and photophysical methods, with particular emphasis placed on probing triplet excited state properties. A counter-intuitive trend of increasing fluorescence quantum efficiency and lifetime with decreasing excited state energy (optical gap) is observed across the series of DAD chromophores. Careful study of the excited state dynamics, including triplet yields (as inferred from singlet oxygen sensitization), reveals that the underlying origin of the unusual trend in the fluorescence parameters is that the singlet–triplet intersystem crossing rate and yield decrease with decreasing optical gap. It is concluded that the rate of intersystem crossing decreases as the LUMO is increasingly localized on the acceptor unit in the DAD chromophore, and this result is interpreted as arising because the extent of spin–orbit coupling induced by the platinum heavy metal centers decreases as the LUMO is more localized on the acceptor. In addition to the trend in intersystem crossing, the results show that the triplet decay rates follow the Energy Gap Law correlation over a 1.8 eV range of triplet energy and 1000-fold range of triplet decay rates. Finally, femtosecond transient absorption studies for the DAD chromophores reveals a strong absorption in the near-infrared region which is attributed to the singlet excited state. This spectral band appears to be general for DAD chromophores, and may be a signature of the charge transfer (CT) singlet excited state.

In order to understand the photophysics and non-linear optical properties of carbazole containing π-conjugated oligomers of the type ET-Cbz-TE (E = ethynylene, T = 2,5-thienylene, Cbz = 3,6-carbazole), a detailed investigation was carried out on a series of oligomers that feature Au(I) or Pt(II) acetylide “end groups”, as well as a Pt(II)-acetylide linked polymer (CBZ-Au-1 and CBZ-Pt-1, CBZ-Poly-Pt). These organometallic chromophores were characterized by UV-visible absorption and variable temperature photoluminescence spectroscopy, nanosecond transient absorption spectroscopy, open aperture nanosecond z-scan and two photon absorption (2PA) spectroscopy. The Au(I) and Pt(II) oligomers and polymer exhibit weak fluorescence in fluid solution at room temperature. Efficient phosphorescence is observed from the Pt(II) systems below 150 K in a solvent glass; however, the Au(I) oligomer exhibits only weak phosphorescence at 77 K. Taken together, the emission results indicate that the intersystem crossing efficiency for the Pt(II) chromophores is greater than for the Au(I) oligomer. Nonetheless, nanosecond transient absorption indicates that direct excitation affords moderately long-lived triplet states for all of the chromophores. Open aperture z-scan measurement shows effective optical attenuation can be achieved by using these materials. The 2PA cross section in the degenerate S0→S1 transition region was in the range 10–100 GM, and increased monotonically toward shorter wavelengths, reaching 800–1000 GM at 550 nm.

Direct detection of pyrophosphate (PPi) in aqueous solution is demonstrated using a cationic poly(phenylene-ethynylene) with polyamine side chains. Pyrophosphate-induced polymer aggregation causes a significant spectroscopic change, which in turn allows quantification of dissolved PPi using ratiometric signals.

The preparation of Pt(II) complexes of the type trans-L2Pt(Ar)Cl, L2Pt(Ar)2, and L2Pt(Ar)(Ar′) (L = PBu3, Ar = arylene) by CuI catalyzed reaction of cis-(PBu3)2PtCl2 with aryl-stannanes is reported. The reactions proceed at 25–60 °C in moderate to good yields. The reaction is demonstrated to occur with phenyl- and 2-thienyl-stannanes that include a variety of functionality, and all of the resulting Pt-aryl complexes were fully characterized by 1H, 13C, and 31PNMR spectroscopy, as well as mass spectroscopy. Photophysical properties of the L2Pt(Ar)2, and L2Pt(Ar)(Ar′) complexes were measured, including steady-state absorption, photoluminescence, and photoluminescence quantum yields, in order to understand how attachment of the platinum metal influences the excited state properties of the arylene ligands. This work affirms that CuI catalyzed coupling between Ar–SnR3 and L2PtCl2 is a useful platinum–carbon bond formation reaction.

A series of trans-N-heterocyclic carbene (NHC) platinum(II) acetylide complexes of the form (ICy)2Pt(R)2 (where ICy = 1,3-bis-(cyclohexyl)imidazol-2-ylidene and R = 1-Ethynyl-4-(phenylethynyl)benzene (PE2), 2-(9,9-Diethyl-9H-fluoren-7-yl)benzo[d]thiazole (BTF), and 9,9-Diethyl-7-ethynyl-N,N-diphenyl-9H-fluoren-2-amine (DPAF), 2a–c respectively), were synthesized via Hagihara reaction of the unprotected aryl-acetylide ligands with trans-(ICy)2PtCl2 (1) in 47–73% yield. Precursor 1 was generated in a one-pot synthesis via formation of a silver carbene precursor followed by transmetallation, and was obtained in high yield (95%). The single-crystal X-ray structures of 1, 2a–c were determined and analyzed. The photophysical properties of 2a–c were compared to their respective tributyl phosphine (PBu3) analogues. The optical properties of the series were studied by UV-Vis spectroscopy, photoluminescence spectroscopy, nanosecond transient absorption spectroscopy, and open aperture nanosecond z-scan. Coupling of the organic chromophores to the platinum center affords efficient intersystem crossing as concluded by the complexes’ low fluorescence quantum yields, efficient phosphorescence and intense T1 − Tn absorption. Open aperture z-scan with 606 nm, 10 ns laser pulses showed comparable optical attenuation relative to a standard sample of (PBu3)2Pt(DPAF)2 (3c). Pulse limiting was achieved via a dual-mechanism of two-photon absorption (2PA) coupled with excited-state absorption (ESA). TD-DFT Computations were also employed for 2a–c to give greater insight into the nature of the singlet-singlet electronic transitions.

The long-lived excited state in a series of metal–organic phenyleneethynylene oligomers is probed by UV-visible and infrared transient absorption spectroscopy.