The following Ag^I bis(pyrazolyl)methane complexes with BF₄^–/NO₃^– as counteranions were synthesized and characterized: [Ag(L^pzH)]₂(NO₃)₂ (1), [Ag(L^pzMe)]₂(NO₃)₂ (2), [Ag(L^pzH)]_n(BF₄)_n (3), and [Ag(L^pzMe)]_n(BF₄)_n (4) [L^pzH = bis(pyrazolyl)methane; L^pzMe = bis(3,5-dimethylpyrazolyl)methane]. These complexes were prepared to identify optimum precursors for the thermolytic deposition of metallic silver. The crystal structures of 1 and 2 show that the complexes are dinuclear and that the NO₃^– anions interact with the metals. In contrast, 3 is polymeric and the BF₄^– does not interact with the metal. When crystallizing 1–4 in non-anhydrous solvents, the presence of adventitious water further reacts with 3 and 4 (but not with 1 and 2) to yield dinuclear complexes [Ag(L^pzH)(H₂O)₂]₂(BF₄)₂ (3a) and [Ag(L^pzMe)(H₂O)₂]₂(BF₄)₂ (4a). All of the dinuclear species 1, 2, 3a and 4a exhibit an argentophilic interaction with Ag···Ag distances in the range 3.18–2.99 Å. Thermogravimetric analysis (TGA) shows that 1 and 2 have lower decomposition temperatures (231 and 255 °C, respectively) than 3 and 4 (298 and 331 °C, respectively). 2 was further investigated as a precursor for metallic silver deposition by spin-coating solutions (10^–3 m, THF/DMSO, 4:1), followed by annealing at 310 °C on 52100 steel substrates. According to energy-dispersive X-ray spectroscopy (EDS) and scanning electron microscopy (SEM) the metal deposition proceeds primarily via an island growth (Volmer–Weber) mechanism.

The synthesis, characterization, and optical properties of a novel star-shaped oligothiophene with a central rigid trithienobenzene (BTT) core and diketopyrrolopyrrole (DPP) units are reported and compared with homologous linear systems based on the benzodithiophene (BDT) and the naphthodithiophene (NDT) units end capped with DPPs. This comparison is aimed at elucidating the effect of the star-shaped configuration versus linear conformation on the optical and electrical properties. Electronic and vibrational spectroscopies, together with transient absorption spectroscopy, scanning electronic microscopy, and DFT calculations are used to understand not only the molecular properties of these semiconductors, but also to analyze the supramolecular aggregation in these derivatives. We conclude that although the subject star-shaped derivative is not optimal in terms of π-conjugation, its extended BTT unit significantly favors intermolecular π-stacking interactions, which is interesting for their applications in devices. Field-effect transistors and solar cells were fabricated with these new molecular semiconductors and the performance difference discussed.

Solution-processed polymer-based logic circuits are typically associated with high operating voltage and slow switching speeds. Here, polymer field-effect transistors (PFETs) fabricated on hybrid self-assembled nanodielectric (SAND) structures are reported, the latter consisting of alternating organic–inorganic layers exhibiting low leakage current (≈10⁻⁹ A cm⁻²) and high capacitance (≈0.8 μF cm⁻²). Suitable device engineering, controllable dielectric parameters, and interface energetics enable PFET operation at ±1 V, field-effect mobility (μ _FET) > 2.0 cm² V⁻¹ s⁻¹, subthreshold swing ≈100 mV dec⁻¹, and switching response ≈150 ns. These performance parameters are orders of magnitude higher than similar devices fabricated from other polymer dielectrics. Inverter and NAND logic circuits fabricated from these SAND-based PFETs possess voltage gain up to 38 and maximum-frequency bandwidth of 2 MHz. A systematic study comparing different classes of dielectric and semiconducting material attributes the enhanced performance to improved relaxation dynamics of the SAND layer and tunable chemically functionalized interfaces.

The nature of charge transport and local structure are investigated in amorphous indium oxide-based thin films fabricated by spin-coating. The In–X–O series where X = Sc, Y, or La is investigated to understand the effects of varying both the X cation ionic radius (0.89–1.17 Å) and the film processing temperature (250–300 °C). Larger cations in particular are found to be very effective amorphosizers and enable the study of high mobility (up to 9.7 cm² V⁻¹ s⁻¹) amorphous oxide semiconductors without complex processing. Electron mobilities as a function of temperature and gate voltage are measured in thin-film transistors, while X-ray absorption spectroscopy and ab initio molecular dynamics simulations are used to probe local atomic structure. It is found that trap-limited conduction and percolation-type conduction mechanisms convincingly model transport for low- and high-temperature processed films, respectively. Increased cation size leads to increased broadening of the tail states (10–23 meV) and increased percolation barrier heights (24–55 meV) in the two cases. For the first time in the amorphous In–X–O system, such effects can be explained by local structural changes in the films, including decreased In–O and In–M (M = In, X) coordination numbers, increased bond length disorder, and changes in the MO _x polyhedra interconnectivity.

Three new fused thiophene semiconductors, end-capped with diperfluorophenylthien-2-yl (DFPT) groups (DFPT-thieno[2′,3′:4,5]thieno[3,2-b]thieno[2,3-d]thiophene (TTA), DFPT-dithieno[2,3-b:3′,2′-d]thiophenes (DTT), and DFPT-thieno[3,2-b]thiophene (TT)), are synthesized and characterized in organic thin film transistors. Good environmental stability of the newly developed materials is demonstrated via thermal analysis as well as degradation tests under white light. The molecular structures of all three perfluorophenylthien-2-yl end-functionalized derivatives are determined by single crystal X-ray diffraction. DFPT-TTA and DFPT-TT exhibit good n-type TFT performance, with mobilities up to 0.43 and 0.33 cm² V⁻¹ s⁻¹, respectively. These are among the best performing n-type materials of all fused thiophenes reported to date. The best thin film transistor device performance is achieved via an n-octadecyltrichlorosilane dielectric surface treatment on the thermally grown Si/SiO₂ substrates prior to vapor-phase semiconductor deposition. Within the DFPT series, carrier mobility magnitudes depend strongly on the semiconductor growth conditions and the gate dielectric surface treatment.

The reaction of γ-alumina with tetraethylorthosilicate (TEOS) vapor at low temperatures selectively yields monomeric SiO_x species on the alumina surface. These isolated (-AlO)₃Si(OH) sites are characterized by PXRD, XPS, DRIFTS of adsorbed NH₃, CO, and pyridine, and ²⁹Si and ²⁷Al DNP-enhanced solid-state NMR spectroscopy. The formation of isolated sites suggests that TEOS reacts preferentially at strong Lewis acid sites on the γ-Al₂O₃ surface, functionalizing the surface with “mild” Brønsted acid sites. For liquid-phase catalytic cyclohexanol dehydration, these SiO_x sites exhibit up to 3.5-fold higher specific activity than the parent alumina with identical selectivity.

The reaction of γ-alumina with tetraethylorthosilicate (TEOS) vapor at low temperatures selectively yields monomeric SiO_x species on the alumina surface. These isolated (-AlO)₃Si(OH) sites are characterized by PXRD, XPS, DRIFTS of adsorbed NH₃, CO, and pyridine, and ²⁹Si and ²⁷Al DNP-enhanced solid-state NMR spectroscopy. The formation of isolated sites suggests that TEOS reacts preferentially at strong Lewis acid sites on the γ-Al₂O₃ surface, functionalizing the surface with “mild” Brønsted acid sites. For liquid-phase catalytic cyclohexanol dehydration, these SiO_x sites exhibit up to 3.5-fold higher specific activity than the parent alumina with identical selectivity.

π-conjugated polymers based on the electron-neutral alkoxy-functionalized thienyl-vinylene (TVTOEt) building-block co-polymerized, with either BDT (benzodithiophene) or T2 (dithiophene) donor blocks, or NDI (naphthalenediimide) as an acceptor block, are synthesized and characterized. The effect of BDT and NDI substituents (alkyl vs alkoxy or linear vs branched) on the polymer performance in organic thin film transistors (OTFTs) and all-polymer organic photovoltaic (OPV) cells is reported. Co-monomer selection and backbone functionalization substantially modifies the polymer MO energies, thin film morphology, and charge transport properties, as indicated by electrochemistry, optical spectroscopy, X-ray diffraction, AFM, DFT calculations, and TFT response. When polymer P7 is used as an OPV acceptor with PTB7 as a donor, the corresponding blend yields TFTs with ambipolar mobilities of μ_e = 5.1 × 10⁻³ cm² V^–1 s^–1 and μ_h = 3.9 × 10⁻³ cm² V^–1 s^–1 in ambient, among the highest mobilities reported to date for all-polymer bulk heterojunction TFTs, and all-polymer solar cells with a power conversion efficiency (PCE) of 1.70%, the highest reported PCE to date for an NDI-polymer acceptor system. The stable transport characteristics in ambient and promising solar cell performance make NDI-type materials promising acceptors for all-polymer solar cell applications.

The two classic structural classifications of solid matter, crystalline and amorphous, are quite useful for inorganic solids, from antimony trichloride to zinc dibromide and beyond. However, for many molecular materials, especially those based on components containing ten or more non-hydrogen atoms, ordered single crystals are less common, and intermediate structures that are neither amorphous nor crystalline frequently dominate. Herein, we discuss several situations in which there is local (or partial) ordering in such molecular materials. These materials go beyond the standard concepts concerning polymers and must account for imperfect but substantial local ordering, such as that caused by weak intermolecular interactions (e.g., π stacking, H-bonding, and/or dispersion forces). This local ordering has important implications for, and applications in, materials properties: we specifically consider dielectric response, electron transport, and exciton transfer. Finally, we discuss the fundamental importance of the effective dimensionality of partially ordered domains in molecular materials.

Organic photovoltaics (OPVs) offer the opportunity for cheap, lightweight and mass-producible devices. However, an incomplete understanding of the charge generation process, in particular the timescale of dynamics and role of exciton diffusion, has slowed further progress in the field. We report a new Kinetic Monte Carlo model for the exciton dissociation mechanism in OPVs that addresses the origin of ultra-fast (<1 ps) dissociation by incorporating exciton delocalization. The model reproduces experimental results, such as the diminished rapid dissociation with increasing domain size, and also lends insight into the interplay between mixed domains, domain geometry, and exciton delocalization. Additionally, the model addresses the recent dispute on the origin of ultra-fast exciton dissociation by comparing the effects of exciton delocalization and impure domains on the photo-dynamics.This model provides insight into exciton dynamics that can advance our understanding of OPV structure–function relationships.

Organic photovoltaics (OPVs) offer the opportunity for cheap, lightweight and mass-producible devices. However, an incomplete understanding of the charge generation process, in particular the timescale of dynamics and role of exciton diffusion, has slowed further progress in the field. We report a new Kinetic Monte Carlo model for the exciton dissociation mechanism in OPVs that addresses the origin of ultra-fast (<1 ps) dissociation by incorporating exciton delocalization. The model reproduces experimental results, such as the diminished rapid dissociation with increasing domain size, and also lends insight into the interplay between mixed domains, domain geometry, and exciton delocalization. Additionally, the model addresses the recent dispute on the origin of ultra-fast exciton dissociation by comparing the effects of exciton delocalization and impure domains on the photo-dynamics.This model provides insight into exciton dynamics that can advance our understanding of OPV structure–function relationships.

The molecular packing motifs within crystalline domains should be a key determinant of charge transport in thin-film transistors (TFTs) based on small organic molecules. Despite this implied importance, detailed information about molecular organization in polycrystalline thin films is not available for the vast majority of molecular organic semiconductors. Considering the potential of fused thiophenes as environmentally stable, high-performance semiconductors, it is therefore of interest to investigate their thin film microstructures in relation to the single crystal molecular packing and OTFT performance. Here, the molecular packing motifs of several new benzo[d,d′]thieno[3,2-b;4,5-b′]dithiophene (BTDT) derivatives are studied both in bulk 3D crystals and as thin films by single crystal diffraction and grazing incidence wide angle X-ray scattering (GIWAXS), respectively. The results show that the BTDT derivative thin films can have significantly different molecular packing from their bulk crystals. For phenylbenzo[d,d′]thieno[3,2-b;4,5-b′]dithiophene (P-BTDT), 2-biphenylbenzo[d,d′]thieno-[3,2-b;4,5-b′]dithiophene (Bp-BTDT), 2-naphthalenylbenzo[d,d′]thieno[3,2-b;4,5-b′]dithiophene (Np-BTDT), and bisbenzo[d,d′]thieno[3,2-b;4,5-b′]dithiophene (BBTDT), two lattices co-exist, and are significantly strained versus their single crystal forms. For P-BTDT, the dominance of the more strained lattice relative to the bulk-like lattice likely explains the high carrier mobility. In contrast, poor crystallinity and surface coverage at the dielectric/substrate interface explains the marginal OTFT performance of seemingly similar PF-BTDT films.

Chemisorption of the activated metallocene polymerization catalyst derived from [rac-ethylenebisindenyl]zirconium dichlororide (EBIZrCl₂) on the native Al₂O₃ surfaces of metallic aluminum nanoparticles, followed by exposure to propylene, affords 0–3 metal-isotactic polypropylene nanocomposites. The microstructures of these nanocomposites are characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and atomic force microscopy. Electrical measurements show that increasing the concentration of the filler nanoparticles increases the effective permittivity of the nanocomposites to ϵ_r values as high as 15.4. Because of the high contrast in the complex permittivities and conductivities between the metallic aluminum nanoparticles and the polymeric polypropylene matrix, these composites obey the percolation law for two-phase composites, reaching maximum permittivities just before the percolation threshold volume fraction, v_f ≈ 0.16. This unique method of in situ polymerization from the surface of metallic Al particles produces a new class of materials that perform as superior pulse-power capacitors, with low leakage current densities of ≈10⁻⁷–10⁻⁹ A/cm² at an applied field of 10⁵ V/cm, low dielectric loss in the 100 Hz–1 MHz frequency range, and recoverable energy storage as high as 14.4 J/cm³.

A new family of naphthalimide-fused thienopyrazine derivatives for ambipolar charge transport in organic field-effect transistors is presented. Their electronic and molecular structures were elucidated through optical and vibrational spectroscopy aided by DFT calculations. The results indicate that these compounds have completely planar molecular skeletons which promote good film crystallinity and low reorganization energies for both electron and hole transport. Their performance in organic field-effect transistors is compared with twisted and planar naphthaleneamidine monoimide-fused terthiophenes in order to understand the origin of ambipolarity in this new series of molecular semiconductors.

Facile one-pot [1 + 1 + 2] and [2 + 1 + 1] syntheses of thieno[3,2-b]thieno[2′,3′:4,5]thieno[2,3-d]thiophene (tetrathienoacene; TTA) semiconductors are described which enable the efficient realization of a new TTA-based series for organic thin-film transistors (OTFTs). For the perfluorophenyl end-functionalized derivative DFP-TTA, the molecular structure is determined by single-crystal X-ray diffraction. This material exhibits n-channel transport with a mobility as high as 0.30 cm²V⁻¹s⁻¹ and a high on-off ratio of 1.8 × 10⁷. Thus, DFP-TTA has one of the highest electron mobilities of any fused thiophene semiconductor yet discovered. For the phenyl-substituted analogue, DP-TTA, p-channel transport is observed with a mobility as high as 0.21 cm²V⁻¹s⁻¹. For the 2-benzothiazolyl (BS-) containing derivative, DBS-TTA, p-channel transport is still exhibited with a hole mobility close to 2 × 10⁻³ cm²V⁻¹s⁻¹. Within this family, carrier mobility magnitudes are strongly dependent on the semiconductor growth conditions and the gate dielectric surface treatment.

The performance of bottom-contact thin-film transistor (TFT) structures lags behind that of top-contact structures owing to the far greater contact resistance. The major sources of the contact resistance in bottom-contact TFTs are believed to reflect a combination of non-optimal semiconductor growth morphology on the metallic contact surface and the limited available charge injection area versus top-contact geometries. As a part of an effort to understand the sources of high charge injection barriers in n-channel TFTs, the influence of thiol metal contact treatment on the molecular-level structures of such interfaces is investigated using hexamethyldisilazane (HMDS)-treated SiO₂ gate dielectrics. The focus is on the self-assembled monolayer (SAM) contact surface treatment methods for bottom-contact TFTs based on two archetypical n-type semiconductors, α,ω-diperfluorohexylquarterthiophene (DFH-4T) and N,N′bis(n-octyl)-dicyanoperylene-3,4:9,10-bis(dicarboximide) (PDI-8CN₂). TFT performance can be greatly enhanced, to the level of the top contact device performance in terms of mobility, on/off ratio, and contact resistance. To analyze the molecular-level film structural changes arising from the contact surface treatment, surface morphologies are characterized by atomic force microscopy (AFM) and scanning tunneling microscopy (STM). The high-resolution STM images show that the growth orientation of the semiconductor molecules at the gold/SAM/semiconductor interface preserves the molecular long axis orientation along the substrate normal. As a result, the film microstructure is well-organized for charge transport in the interfacial region.

Many machines operate in harsh environments where elevated temperatures require careful consideration of the lubricant for optimal performance. Lubricant additives can be designed to improve properties of base oil at specific temperature ranges. In the present work, two [tris(phosphino)borate]AgL (L = PEt₃; NHC) complexes are synthesized and added to engine oil at various concentrations. The complexes thermolyze between 200 and 300 °C, yielding metallic Ag. A mixture of engine oil and the silver-based nanoparticles provides fully flooded lubrication for pin-on-disk friction tests. A thermo-elastohydrodynamic model for point contact is utilized to predict the pin loads at which flash temperatures between 200 and 300 °C occur, thus inducing thermal decomposition of the complexes. Results of the friction tests and wear measurements indicate a significant reduction in wear at 0.5–1.0% Ag complex weight concentrations and little change in friction. The improved wear performance is attributed to the thermolysis and deposition of the silver-based complexes in the wear scar, as confirmed by energy-dispersive X-ray analysis.

Herein, we report a new family of naphthaleneamidinemonoimide-fused oligothiophene semiconductors designed for facile charge transport in organic field-effect transistors (OFETs). These molecules have planar skeletons that induce high degrees of crystallinity and hence good charge-transport properties. By modulating the length of the oligothiophene fragment, the majority carrier charge transport can be switched from n-type to ambipolar behavior. The highest FET performance is achieved for solution-processed films of 10-[(2,2′-bithiophen)-5-yl]-2-octylbenzo[lmn]thieno[3′,4′:4,5]imidazo[2,1-b][3,8]phenanthroline-1,3,6(2 H)-trione (NDI-3 Tp), with optimized film mobilities of 2×10⁻² and 0.7×10⁻² cm² V⁻¹ s⁻¹ for electrons and holes, respectively. Finally, these planar semiconductors are compared with their twisted-skeleton counterparts, which exhibit only n-type mobility, in order to understand the origin of the ambipolarity in this new series of molecular semiconductors.

Here, means to enhance power conversion efficiency (PCE or η) in bulk-heterojunction (BHJ) organic photovoltaic (OPV) cells by optimizing the series resistance (R_s)—also known as the cell internal resistance—are studied. It is shown that current state-of-the-art BHJ OPVs are approaching the limit for which efficiency can be improved via R_s reduction alone. This evaluation addresses OPVs based on a poly(3-hexylthiophene):6,6-phenyl C₆₁-butyric acid methyl ester (P3HT:PCBM) active layer, as well as future high-efficiency OPVs (η > 10%). A diode-based modeling approach is used to assess changes in R_s. Given that typical published P3HT:PCBM test cells have relatively small areas (∼0.1 cm²), the analysis is extended to consider efficiency losses for larger area cells and shows that the transparent anode conductivity is then the dominant materials parameter affecting R_s efficiency losses. A model is developed that uses cell sizes and anode conductivities to predict current–voltage response as a function of resistive losses. The results show that the losses due to R_s remain minimal until relatively large cell areas (>0.1 cm²) are employed. Finally, R_s effects on a projected high-efficiency OPV scenario are assessed, based on the goal of cell efficiencies >10%. Here, R_s optimization effects remain modest; however, there are now more pronounced losses due to cell size, and it is shown how these losses can be mitigated by using higher conductivity anodes.

The temperature dependence of field-effect transistor (FET) mobility is analyzed for a series of n-channel, p-channel, and ambipolar organic semiconductor-based FETs selected for varied semiconductor structural and device characteristics. The materials (and dominant carrier type) studied are 5,5′′′-bis(perfluorophenacyl)-2,2′:5′,2″:5″,2′′′-quaterthiophene (1, n-channel), 5,5′′′-bis(perfluorohexyl carbonyl)-2,2′:5′,2″:5″,2′′′-quaterthiophene (2, n-channel), pentacene (3, p-channel); 5,5′′′-bis(hexylcarbonyl)-2,2′:5′,2″:5″,2′′′-quaterthiophene (4, ambipolar), 5,5′′′-bis-(phenacyl)-2,2′: 5′,2″:5″,2′′′-quaterthiophene (5, p-channel), 2,7-bis((5-perfluorophenacyl)thiophen-2-yl)-9,10-phenanthrenequinone (6, n-channel), and poly(N-(2-octyldodecyl)-2,2′-bithiophene-3,3′-dicarboximide) (7, n-channel). Fits of the effective field-effect mobility (µ_eff) data assuming a discrete trap energy within a multiple trapping and release (MTR) model reveal low activation energies (E_As) for high-mobility semiconductors 1–3 of 21, 22, and 30 meV, respectively. Higher E_A values of 40–70 meV are exhibited by 4–7-derived FETs having lower mobilities (µ_eff). Analysis of these data reveals little correlation between the conduction state energy level and E_A, while there is an inverse relationship between E_A and µ_eff. The first variable-temperature study of an ambipolar organic FET reveals that although n-channel behavior exhibits E_A = 27 meV, the p-channel regime exhibits significantly more trapping with E_A = 250 meV. Interestingly, calculated free carrier mobilities (µ₀) are in the range of ∼0.2–0.8 cm² V⁻¹ s⁻¹ in this materials set, largely independent of µ_eff. This indicates that in the absence of charge traps, the inherent magnitude of carrier mobility is comparable for each of these materials. Finally, the effect of temperature on threshold voltage (V_T) reveals two distinct trapping regimes, with the change in trapped charge exhibiting a striking correlation with room temperature µ_eff. The observation that E_A is independent of conduction state energy, and that changes in trapped charge with temperature correlate with room temperature µ_eff, support the applicability of trap-limited mobility models such as a MTR mechanism to this materials set.

The effects of anode/active layer interface modification in bulk-heterojunction organic photovoltaic (OPV) cells is investigated using poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and/or a hole-transporting/electron-blocking blend of 4,4′-bis[(p-trichlorosilylpropylphenyl)-phenylamino]biphenyl (TPDSi₂) and poly[9,9-dioctylfluorene-co-N-[4-(3-methylpropyl)]-diphenylamine] (TFB) as interfacial layers (IFLs). Current–voltage data in the dark and AM1.5G light show that the TPDSi₂:TFB IFL yields MDMO-PPV:PCBM OPVs with substantially increased open-circuit voltage (V_oc), power conversion efficiency, and thermal stability versus devices having no IFL or PEDOT:PSS. Using PEDOT:PSS and TPDSi₂:TFB together in the same cell greatly reduces dark current and produces the highest V_oc (0.91 V) by combining the electron-blocking effects of both layers. ITO anode pre-treatment was investigated by X-ray photoelectron spectroscopy to understand why oxygen plasma, UV ozone, and solvent cleaning markedly affect cell response in combination with each IFL. O₂ plasma and UV ozone treatment most effectively clean the ITO surface and are found most effective in preparing the surface for PEDOT:PSS deposition; UV ozone produces optimum solar cells with the TPDSi₂:TFB IFL. Solvent cleaning leaves significant residual carbon contamination on the ITO and is best followed by O₂ plasma or UV ozone treatment.

Lanthanide-organic complexes of the general type [Ln{N(SiMe₃)₂}₃] (Ln=La, Sm, Y, Lu) serve as effective precatalysts for the rapid, exo-selective, and highly regioselective tandem double intramolecular hydroalkoxylation/cyclization of primary and secondary dialkynyl dialcohols to yield the corresponding bi-exocyclic enol ethers. Conversions are highly selective with products distinctly different from those generally produced by conventional transition metal or other catalysts, and the turnover frequencies with some substrates are too large to determine accurately. The rates of terminal alkynl alcohol hydroalkoxylation/cyclization are significantly more rapid than those of internal alkynyl alcohols, arguing that steric demands dominate the cyclization transition state. The hydroalkoxylation/cyclizations of internal dialkynyl dialcohols afford excellent E selectivity. The rate law for dialkynyl dialcohol hydroalkoxylation/cyclization is first-order in [catalyst] and zero-order in [alkynyl alcohol], as is observed for the organolanthanide-catalyzed hydroamination/cyclization of aminoalkenes, aminoalkynes, and aminoallenes, and the intramolecular single-step hydroalkoxylation/cyclization of alkynyl alcohols. An ROH/ROD kinetic isotope effect of 0.82(0.02) is observed for the tandem double hydroalkoxylation/cyclization. These mechanistic data implicate turnover-limiting insertion of CC unsaturation into the LnO bond, involving a highly organized transition state, with subsequent, rapid Ln–C protonolysis.

Electron-transporting organic semiconductors (n-channel) for field-effect transistors (FETs) that are processable in common organic solvents or exhibit air-stable operation are rare. This investigation addresses both these challenges through rational molecular design and computational predictions of n-channel FET air-stability. A series of seven phenacyl–thiophene-based materials are reported incorporating systematic variations in molecular structure and reduction potential. These compounds are as follows: 5,5′′′-bis(perfluorophenylcarbonyl)-2,2′:5′,- 2′′:5′′,2′′′-quaterthiophene (1), 5,5′′′-bis(phenacyl)-2,2′:5′,2′′: 5′′,2′′′-quaterthiophene (2), poly[5,5′′′-(perfluorophenac-2-yl)-4′,4′′-dioctyl-2,2′:5′,2′′:5′′,2′′′-quaterthiophene) (3), 5,5′′′-bis(perfluorophenacyl)-4,4′′′-dioctyl-2,2′:5′,2′′:5′′,2′′′-quaterthiophene (4), 2,7-bis((5-perfluorophenacyl)thiophen-2-yl)-9,10-phenanthrenequinone (5), 2,7-bis[(5-phenacyl)thiophen-2-yl]-9,10-phenanthrenequinone (6), and 2,7-bis(thiophen-2-yl)-9,10-phenanthrenequinone, (7). Optical and electrochemical data reveal that phenacyl functionalization significantly depresses the LUMO energies, and introduction of the quinone fragment results in even greater LUMO stabilization. FET measurements reveal that the films of materials 1, 3, 5, and 6 exhibit n-channel activity. Notably, oligomer 1 exhibits one of the highest μ_e (up to ≈0.3 cm² V⁻¹ s⁻¹) values reported to date for a solution-cast organic semiconductor; one of the first n-channel polymers, 3, exhibits μ_e≈10⁻⁶ cm² V⁻¹ s⁻¹ in spin-cast films (μ_e=0.02 cm² V⁻¹ s⁻¹ for drop-cast 1:3 blend films); and rare air-stable n-channel material 5 exhibits n-channel FET operation with μ_e=0.015 cm² V⁻¹ s⁻¹, while maintaining a large I_on:off=10⁶ for a period greater than one year in air. The crystal structures of 1 and 2 reveal close herringbone interplanar π-stacking distances (3.50 and 3.43 Å, respectively), whereas the structure of the model quinone compound, 7, exhibits 3.48 Å cofacial π-stacking in a slipped, donor-acceptor motif.

Lanthanide triflate complexes of the type [Ln(OTf)₃] (Ln=La, Sm, Nd, Yb, Lu) serve as effective, recyclable catalysts for the rapid intramolecular hydroalkoxylation (HO)/cyclization of primary/secondary and aliphatic/aromatic hydroxyalkenes in imidazolium-based room-temperature ionic liquids (RTILs) to yield the corresponding furan, pyran, spirobicyclic furan, spirobicyclic furan/pyran, benzofuran, and isochroman derivatives. Products are straightforwardly isolated from the catalytic solution, conversions exhibit Markovnikov regioselectivity, and turnover frequencies are as high as 47 h⁻¹ at 120 °C. The ring-size rate dependence of the primary alkenol cyclizations is 5>6, consistent with a sterically controlled transition state. The hydroalkoxylation/cyclization rates of terminal alkenols are slightly more rapid than those of internal alkenols, which suggests modest steric demands in the cyclic transition state. Cyclization rates of aryl-functionalized hydroxyalkenes are more rapid than those of the linear alkenols, whereas five- and five/six-membered spirobicyclic skeletons are also regioselectively closed. In cyclization of primary, sterically encumbered alkenols, turnover-frequency dependence on metal-ionic radius decreases by approximately 80-fold on going from La³⁺ (1.160 Å) to Lu³⁺ (0.977 Å), presumably reflecting steric impediments along the reaction coordinate. The overall rate law for alkenol hydroalkoxylation/cyclization is v≈k[catalyst]¹[alkenol]¹. An observed ROH/ROD kinetic isotope effect of 2.48 (9) is suggestive of a catalytic pathway that involves kinetically significant intramolecular proton transfer. The present activation parameters—enthalpy (ΔH^≠)=18.2 (9) kcal mol⁻¹, entropy (ΔS^≠)=−17.0 (1.4) eu, and energy (E_a)=18.2 (8) kcal mol⁻¹—suggest a highly organized transition state. Proton scavenging and coordinative probing results suggest that the lanthanide triflates are not simply precursors of free triflic acid. Based on the kinetic and mechanistic evidence, the proposed catalytic pathway invokes hydroxyl and olefin activation by the electron-deficient Ln³⁺ center, and intramolecular H⁺ transfer, followed by alkoxide nucleophilic attack with ring closure.

This contribution presents an electrochemical, Raman spectroscopic, and theoretical study probing the differences in molecular and electronic structure of two quinoidal oligothiophenes (3′,4′-dibutyl-5,5″-bis(dicyanomethylene)-5,5″-dihydro-2,2′:5′,2″-terthiophene and 5,5′-bis(dicyanomethylene)-3-hexyl-2,5-dihydro-4,4′-dihexyl-2,2′,5,5′-tetrahydro-tetrathiophene) with terminal tetracyanomethylene functionalization and aromatic oligothiophenes where acceptor moieties are positioned at lateral positions along the conjugated chain (6,6′-dibutylsulfanyl-[2,2′-bi-[4-dicyanovinylene-4H-cyclopenta[2,1-b:3,4-b′]dithiophene]). In this way, the consequences of linear and cross conjugation are compared and contrasted. From this analysis, it is apparent that organic field-effect transistors fabricated with cross-conjugated tetrathiophene semiconductors should combine the benefits of an electron-donor aromatic chain with strongly electron-accepting tetracyanomethylene substituents. The corresponding organic field-effect transistors exhibit ambipolar transport with rather similar hole and electron mobilities. Moreover, n-channel conduction is enhanced to yield one of the highest electron mobilities found to date for this type of material.

Chain-transfer processes represent highly effective chemical means to achieve selective, in situ d- and f-block-metal catalyzed functionalization of polyolefins. A diverse variety of electron-poor and electron-rich chain-transfer agents, including silanes, boranes, alanes, phosphines, and amines, effect efficient chain termination with concomitant carbon–heteroelement bond formation during single-site olefin-polymerization processes. High polymerization activities, control of polyolefin molecular weight and microstructure, and selective chain functionalization are all possible, with distinctly different mechanisms operative for the electron-poor and electron-rich reagents. A variety of metal centers (early transition metals, lanthanides, late transition metals) and single-site ancillary ligand arrays (metallocene, half-metallocene, non-metallocene) are able to mediate these selective chain-termination/functionalization processes.

Kettenübertragungen sind effiziente und selektive chemische Prozesse für die d- und f-Metall-katalysierte In-situ-Funktionalisierung von Polyolefinen. Eine Reihe höchst unterschiedlicher elektronenarmer wie auch elektronenreicher Kettenüberträger eignet sich dafür, bei der Single-Site-Polymerisation von Olefinen einen selektiven Kettenabbruch mit gleichzeitiger Kohlenstoff-Heteroelement-Verknüpfung herbeizuführen. Als Kettenüberträger finden z. B. Silane, Borane, Alane, Phosphine und Amine Verwendung. Mit ihnen sind hohe Polymerisationsaktivitäten, eine Kontrolle von Molekulargewicht und Mikrostruktur der Polyolefine und eine selektive Kettenfunktionalisierung möglich. Für elektronenarme und elektronenreiche Reagentien findet man deutlich unterschiedliche Mechanismen. Als Katalysatoren für diese selektiven Kettenabbruchs-/Funktionalisierungsprozesse eignen sich vielfältige Metallzentren (frühe Übergangsmetalle, Lanthanoide, späte Übergangsmetalle) und Single-Site-Hilfsliganden (Metallocene, Halbmetallocene, Nichtmetallocene).