Zinc phthalocyanines (ZnPc) have been attached to the peri-position of a perylenemonoimide (PMI) and a perylenemonoanhydride (PMA), affording electron donor–acceptor conjugates 1 and 2, respectively. In addition, a perylene-monoimide-monoanhydride (PMIMA) has been connected to a ZnPc through its imido position to yield the ZnPc-PMIMA conjugate 10. The three conjugates have been studied for photoinduced electron transfer. For ZnPc-PMIMA 10, electron transfer occurs upon both ZnPc and PMIMA excitation, giving rise to a long-lived (340 ps) charge-separated state. For ZnPc-PMI 1 and ZnPc-PMA 2, stabilization of the radical ion pair states by using polar media is necessary. In THF, photoexcitation of either ZnPc or PMI/PMA produces charge-separated states with lifetimes of 375 and 163 ps, respectively.

A new donor–acceptor system, in which the electron donor triphenylamine (TPA) and the electron acceptor C₆₀ are bridged through a cis- or trans-platinum(II) acetylide spacer have been prepared. Ground-state studies were conducted using electrochemistry and UV/Vis spectroscopy. Fluorescence studies suggested that charge transfer is the deactivation mechanism for the singlet excited state, and this was verified by transient absorption spectroscopy. Selective photoexcitation of 1 and 2 at 387 nm leads to a fast charge transfer between the TPA and C₆₀, which gives rise to a radical ion-pair state (TPA^.+–Pt–C₆₀^.−). Our results suggest that charge transfer is favored for the cis configuration while the presence of the trans configuration in the Pt^II diacetylide results in a longer-lived charge separated states.

Two new artificial mimics of the photosynthetic antenna-reaction center complex have been designed and synthesized (BDP-H₂P-C₆₀ and BDP-ZnP-C₆₀). The resulting electron-donor/acceptor conjugates contain a porphyrin (either in its free-base form (H₂P) or as Zn-metalated complex (ZnP)), a boron dipyrrin (BDP), and a fulleropyrrolidine possessing, as substituent of the pyrrolidine nitrogen, an ethylene glycol chain terminating in an amino group C₆₀-X-NH₂ (X=spacer). In both cases, the three different components were connected by s-triazine through stepwise substitution reactions of cyanuric chloride. In addition to the facile synthesis, the star-type arrangement of the three photo- and redox-active components around the central s-triazine unit permits direct interaction between one another, in contrast to reported examples in which the three components are arranged in a linear fashion. The energy- and electron-transfer properties of the resulting electron-donor/acceptor conjugates were investigated by using UV/Vis absorption and emission spectroscopy, cyclic voltammetry, and femtosecond transient absorption spectroscopy. Comparison of the absorption spectra and cyclic voltammograms of BDP-H₂P-C₆₀ and BDP-ZnP-C₆₀ with those of BDP-H₂P, BDP-ZnP and BDP-C₆₀, which were used as references, showed that the spectroscopic and electrochemical properties of the individual constituents are basically retained, although some appreciable shifts in terms of absorption indicate some interactions in the ground state. Fluorescence lifetime measurements and transient absorption experiments helped to elucidate the antenna function of BDP, which upon selective excitation undergoes a rapid and efficient energy transfer from BDP to H₂P or ZnP. This is then followed by an electron transfer to C₆₀, yielding the formation of the singlet charge-separated states, namely BDP-H₂P^.+-C₆₀^.− and BDP-ZnP^.+-C₆₀^.−. As such, the sequence of energy transfer and electron transfer in the present models mimics the events of natural photosynthesis.

Two novel double-alkyl functionalized imidazolium ionic liquid crystals have successfully been utilized to demonstrate the benefits of the liquid crystalline phase on the ssDSSC performance. In particular, a good balance between dye regeneration and hole transport is only realized in the liquid crystalline phase. Devices that employ a single component ionic liquid based electrolyte show a remarkably stable efficiency during 1000 h under outdoor operation temperature conditions and 1 sun illumination.

In a novel electron-donor–acceptor conjugate, phthalocyanine (Pc) and perylenediimide (PDI) are connected through a trans-platinum(II) diacetylide linker to yield Pc-Pt-PDI 1. In the ground state, the presence of Pt^II disrupts the electronic communication between the two electroactive components, as revealed by UV/Vis spectroscopy and electrochemical studies. The photophysical behavior of 1 is compared with that of the corresponding Pc-PDI electron-donor–acceptor conjugate 2 in terms of charge separation and charge recombination. The insertion of Pt^II between Pc and PDI impacts the results in a longer-lived Pc^.+/PDI^.− radical ion-pair state. In addition, the intermediately formed Pc triplet excited state is formed with higher quantum yields in 1 than in 2.

A new series of donor–bridge–acceptor (D–B–A) compounds consisting of π-conjugated oligofluorene (oFL) bridges between a ferrocene (Fc) electron-donor and a fullerene (C₆₀) electron-acceptor have been synthesized. In addition to varying the length of the bridge (i.e., mono- and bi-fluorene derivatives), four different ways of linking ferrocene to the bridge have been examined. The Fc moiety is linked to oFL: 1) directly without any spacer, 2) by an ethynyl linkage, 3) by a vinylene linkage, and 4) by a p-phenylene unit. The electronic interactions between the electroactive species have been characterized by cyclic voltammetry, absorption, fluorescence, and transient absorption spectroscopy in combination with quantum chemical calculations. The calculations reveal exceptionally close energy-matching between the Fc and the oFL units, which results in strong electronic-coupling. Hence, intramolecular charge-transfer may easily occur upon exciting either the oFLs or Fcs. Photoexcitation of Fc–oFL–C₆₀ conjugates results in transient radical-ion-pair states. The mode of linkage of the Fc and FL bridge has a profound effect on the photophysical properties. Whereas intramolecular charge-separation is found to occur rather independently of the distance, the linker between Fc and oFL acts (at least in oFL) as a bottleneck and significantly impacts the intramolecular charge-separation rates, resulting in beta values between β_CS 0.08 and 0.19 Å⁻¹. In contrast, charge recombination depends strongly on the electron-donor–acceptor distance, but not at all on the linker. A value of β_CR (0.35±0.01 Å⁻¹) was found for all the systems studied. Oligofluorenes prove, therefore, to be excellent bridges for probing how small structural variations affect charge transport in D–B–A systems.

The synthesis and photophysical properties of several porphyrin (P)–phthalocyanine (Pc) conjugates (P–Pc; 1–3) are described, in which the phthalocyanines are directly linked to the β-pyrrolic position of a meso-tetraphenylporphyrin. Photoinduced energy- and electron-transfer processes were studied through the preparation of H₂P–ZnPc, ZnP–ZnPc, and PdP–ZnPc conjugates, and their assembly through metal coordination with two different pyridylfulleropyrrolidines (4 and 5). The resulting electron-donor–acceptor hybrids, which were formed by axial coordination of compounds 4 and 5 with the corresponding phthalocyanines, mimicked the fundamental processes of photosynthesis; that is, light harvesting, the transduction of excited-state energy, and unidirectional electron transfer. In particular, photophysical studies confirmed that intramolecular energy-transfer resulted from the S₂ excited state as well as from the S₁ excited state of the porphyrins to the energetically lower-lying phthalocyanines, followed by an intramolecular charge-transfer to yield P–Pc^.+⋅C₆₀^.−. This unique sequence of processes opens the way for solar-energy-conversion processes.

The synthesis and photophysical properties of several fullerene–phthalocyanine–porphyrin triads (1–3) and pentads (4–6) are described. The three photoactive moieties were covalently connected in an one-step synthesis through 1,3-dipolar cycloaddition to C₆₀ of the corresponding azomethine ylides generated in situ by condensation reaction of a substituted N-porphyrinylmethylglycine derivative and an appropriated formyl phthalocyanine or a diformyl phthalocyanine derivative, respectively. ZnP-C₆₀-ZnPc (3), (ZnP)₂-ZnPc-(C₆₀)₂ (6), and (H₂P)₂-ZnPc-(C₆₀)₂ (5) give rise upon excitation of their ZnP or H₂P components to a sequence of energy and charge-transfer reactions with, however, fundamentally different outcomes. With (ZnP)₂-ZnPc-(C₆₀)₂ (6) the major pathway is an highly exothermic charge transfer to afford (ZnP)(ZnP^.+)-ZnPc-(C₆₀^.−)(C₆₀). The lower singlet excited state energy of H₂P (i.e., ca. 0.2 eV) and likewise its more anodic oxidation (i.e., ca. 0.2 V) renders the direct charge transfer in (H₂P)₂-ZnPc-(C₆₀)₂ (5) not competitive. Instead, a transduction of singlet excited state energy prevails to form the ZnPc singlet excited state. This triggers then an intramolecular charge transfer reaction to form exclusively (H₂P)₂-ZnPc^.+-(C₆₀^.−)(C₆₀). A similar sequence is found for ZnP-C₆₀-ZnPc (3).

Phthalocyanine (Pc) dimers connected through trans-platinum(II) diacetylide linkers have been prepared by reaction of the corresponding ethynylphthalocyanines with trans-bis(triethylphosphine)platinum(II) chloride. Special emphasis was placed on the analysis of the ground- and excited-state features of these compounds in relation to butadiyne-bridged Pc dimers and the corresponding monomers. Both Zn^II-containing Pc dimers exhibit long-lived triplet excited states. The insertion of σ-bonded trans-platinum(II) diacetylide spacers decoupled the two Pc groups and led to an appreciable acceleration (by a factor of up to 10) of the radiative and nonradiative decay rate of the singlet and triplet excited states.

Metal coordination was probed as a versatile approach for designing a novel electron donor/acceptor hybrid [PDIpy₄{Ru(CO)Pc}₄] (1), in which four pyridines placed at the bay region of a perylenediimides (PDIpy₄) coordinate with four ruthenium phthalocyanine units [Ru(CO)Pc]. This structural motif was expected to promote strong electronic coupling between the electron donors and the electron acceptor, a hypothesis that was confirmed in a full-fledged physicochemical investigation focusing on the ground and excited state reactivities. As far as the ground state is concerned, absorption and electrochemical assays indeed reveal a notable redistribution of electron density, that is, from the electron-donating [Ru(CO)Pc] to the electron-accepting PDIpy₄. The most important thing to note in this context is that both the [Ru(CO)Pc] oxidation and the PDIpy₄ reduction are rendered more difficult in 1 than in the individual building blocks. Likewise, in the excited state, strong electronic communication is the inception for a rapid charge-transfer process in photoexcited 1. Regardless of exciting [Ru(CO)Pc] or PDIpy₄, spectral characteristics of the [RuPc] radical cation (broad absorptive features from 425 to 600 nm with a maximum at 575 nm, as well as a band centered at 725 nm) and of the PDI radical anion (780 nm maximum) emerge. The correspondingly formed radical ion pair state lasts for up to several hundred picoseconds in toluene, for example. On the other hand, employing more polar solvents, such as dichloromethane, destabilizes the radical ion pair state.

The synthesis of the first fully conjugated tetrathiafulvalene–tetracyano-p-quinodimethane ((TTF)–TCNQ)-type system has been carried out by means of a Julia–Kocienski olefination reaction. In particular, a tetracyanoanthraquinodimethane (TCAQ) formyl derivative and two new sulfonylmethyl-exTTFs (exTTF=2-[9-(1,3-dithiol-2-ylidene)anthracen-10(9H)-ylidene]-1,3-dithiole)—prepared as new building blocks—were linked. A variety of experimental conditions reveal that the use of sodium hexamethyldisilazane (NaHMDS) as base in THF afforded the E olefins with excellent stereoselectivity. Theoretical calculations at the B3LYP/6-31G** level point to highly distorted exTTF and TCAQ that form an almost planar stilbene unit between them. Although calculations predicted appreciable electronic communication between the donor and the acceptor, cyclic voltammetric studies did not substantiate this effect. It was only in photophysical assays that the electronic communication emerged in the form of a charge-transfer (CT) absorption and emission. Once photoexcited (i.e., the locally excited state or excited charge-transfer state), an ultrafast, subpicosecond charge separation leads to a radical ion pair state in which the spectroscopic features of the radical cation of exTTF as well as the radical anion of TCAQ are discernable. The radical ion pair is metastable and undergoes a fast ((1.0±0.2) ps) charge recombination to reconstitute the electronic ground state. Such ultrafast charge separation and recombination processes come as a consequence of the very short vinyl linkage between the two electroactive units.

Two novel supramolecular building blocks, namely cis- and trans-symmetric zinc–porphyrins bearing Hamilton receptors as their focal points (10 and 15), were self-assembled with (i) first-, second- and third-generation depsipeptide cyanurates (21–23); (ii) second-generation dendrofullerene (24), and (iii) cyanuric acid substituted fullerene (20), and probed in a series of photophysical investigations. Importantly, an overall 1:2 stoichiometry was confirmed with binding constants K_n, and Hill coefficients n_H that indicate remarkable cooperativities. As a general feature, stronger binding evolves from the trans-symmetric porphyrin isomer, although the increased steric demand of the depsipeptide ligandsmeans that the binding constants decrease with each generation. The self-assembly of 10 or 15 with 20 affords novel electron donor–acceptor hybrids that reveal, upon excitation,intra-hybrid charge-transfer events.

Several new fullerene–heptamethine conjugates, which absorb as far as into the infrared spectrum as 800 nm, have been synthesized and fully characterized by physicochemical means. In terms of optical and electrochemical characteristics, appreciable electronic coupling between both electroactive species is deduced. The latter also reflect the excited-state features. To this end, time-resolved, transient absorption measurements revealed that photoexcitation is followed by a sequence of charge-transfer events which evolve from higher singlet excited states (i.e., S₂—fast charge transfer) and the lowest singlet excited state of the heptamethine cyanine (i.e., S₁—slow charge transfer), as the electron donor, to either a covalently linked C₆₀ or C₇₀, as the electron acceptor. Finally, charge transfer from photoexcited C₆₀/C₇₀ completes the charge-transfer sequence. The slow internal conversion within the light-harvesting heptamethine cyanine and the strong electronic coupling between the individual constituents are particularly beneficial to this process.

We have realized for the first time a series of truly water-soluble and tightly coupled porphyrin/C₆₀ electron-donor–acceptor conjugates in which the charge separation and charge recombination dynamics are controlled by modifying the nature of the dendrimer and/or the choice of the central metal atom.

The decakis(trifluoromethyl)fullerene C₁-C₇₀(CF₃)₁₀, in which the CF₃ groups are arranged on a para⁷-meta-para ribbon of C₆(CF₃)₂ edge-sharing hexagons, and which has now been prepared in quantities of hundreds of milligrams, was reacted under standard Bingel–Hirsch conditions with a bis-π-extended tetrathiafulvalene (exTTF) malonate derivative to afford a single exTTF₂–C₇₀(CF₃)₁₀ regioisomer in 80 % yield based on consumed starting material. The highly soluble hybrid was thoroughly characterized by using 1D ¹H, ¹³C, and ¹⁹F NMR, 2D NMR, and UV/Vis spectroscopy; matrix-assisted laser desorption ionization (MALDI) mass spectrometry; and electrochemistry. The cyclic voltammogram of the exTTF₂–C₇₀(CF₃)₁₀ dyad revealed an irreversible second reduction process, which is indicative of a typical retro-Bingel reaction; whereas the usual phenomenon of exTTF inverted potentials (>), resulting in a single, two-electron oxidation process, was also observed. Steady-state and time-resolved photolytic techniques demonstrated that the C₁-C₇₀(CF₃)₁₀ singlet excited state is subject to a rapid electron-transfer quenching. The resulting charge-separated states were identified by transient absorption spectroscopy, and radical pair lifetimes of the order of 300 ps in toluene were determined. The exTTF₂–C₇₀(CF₃)₁₀ dyad represents the first example of exploitation of the highly soluble trifluoromethylated fullerenes for the construction of systems able to mimic the photosynthetic process, and is therefore of interest in the search for new materials for photovoltaic applications.

A panchromatic 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene –zinc phthalocyanine conjugate (Bodipy–ZnPc) 1 was synthesized starting from phthalocyanine aldehyde 4, via dipyrromethane 3 and dipyrromethene 2. Conjugate 1 represents the first example in which a Bodipy unit is tethered to the peripheral position of a phthalocyanine core. Electrochemical and optical measurements provided evidence for strong electronic interactions between the Bodipy and ZnPc constituents in the ground state of 1. When conjugate 1 is subjected to photoexcitation in the spectral region corresponding to the Bodipy absorption, the strong fluorescence characteristic of the latter subunit is effectively quenched (i.e., ≥97 %). Excitation spectral analysis confirmed that the photoexcited Bodipy and the tethered ZnPc subunits interact and that intraconjugate singlet energy transfer occurs with an efficiency of ca. 25 %. Treatment of conjugate 1 with N-pyridylfulleropyrrolidine (8), an electron-acceptor system containing a nitrogen ligand, gives rise to the novel electron donor–acceptor hybrid 18 through ligation to the ZnPc center. Irradiation of the resulting supramolecular ensemble within the visible range leads to a charge-separated Bodipy–ZnPc^.+–C₆₀^.− radical-ion-pair state, through a sequence of excited-state and charge transfers, characterized by a remarkably long lifetime of 39.9 ns in toluene.

A novel dendritic C₆₀-H₂P-(ZnP)₃ (P=porphyrin) conjugate gives rise to the successful mimicry of the primary events in photosynthesis, that is, light harvesting, unidirectional energy transfer, charge transfer, and charge-shift reactions. Owing, however, to the flexibility of the linkers that connect the C₆₀, H₂P, and ZnP units, the outcome depends strongly on the rigidity/viscosity of the environment. In an agar matrix or Triton X-100, time-resolved transient absorption spectroscopic analysis and fluorescence-lifetime measurements confirm the following sequence. Initially, light harvesting is seen by the peripheral C₆₀-H₂P- *(ZnP)₃ conjugate. Once photoexcited, a unidirectional energy transfer funnels the singlet excited-state energy to H₂P to form C₆₀-*(H₂P)-(ZnP)₃, which powers an intramolecular charge transfer that oxidizes the photoexcited H₂P and reduces the adjacent C₆₀ species. In the correspondingly formed (C₆₀)^.−-(H₂P)^.+-(ZnP)₃ conjugate, an intramolecular charge-shift reaction generates (C₆₀)^.−-H₂P-(ZnP)₃^.+, in which the radical cation resides on one of the three ZnP moieties, and for which lifetimes of up to 460 ns are found. On the other hand, investigations in organic media (i.e., toluene, THF, and benzonitrile) reveal a short cut, that is, the peripheral ZnP unit reacts directly with C₆₀ to form (C₆₀)^.−-H₂P-(ZnP)₃^.+. Substantial configurational rearrangements— placing ZnP and C₆₀ in proximity to each other—are, however, necessary to ensure the required through space interactions (i.e., close approach). Consequently, the lifetime of (C₆₀)^.−-H₂P-(ZnP)₃^.+ is as short as 100 ps in benzonitrile.

The first pyrrolidine and cyclopropane derivatives of the trimetallic nitride templated (TNT) endohedral metallofullerenes I_h-Sc₃N@C₈₀ and I_h-Y₃N@C₈₀ connected to an electron-donor unit (i.e., tetrathiafulvalene, phthalocyanine or ferrocene) were successfully prepared by 1,3-dipolar cycloaddition reactions of azomethine ylides and Bingel–Hirsch-type reactions. Electrochemical studies confirmed the formation of the [6,6] regioisomers for the Y₃N@C₈₀-based dyads and the [5,6] regioisomers in the case of Sc₃N@C₈₀-based dyads. Similar to other TNT endohedral metallofullerene systems previously synthesized, irreversible reductive behavior was observed for the [6,6]-Y₃N@C₈₀-based dyads, whereas the [5,6]-Sc₃N@C₈₀-based dyads exhibited reversible reductive electrochemistry. Density functional calculations were also carried out on these dyads confirming the importance of these structures as electron transfer model systems. Furthermore, photophysical investigations on a ferrocenyl–Sc₃N@C₈₀-fulleropyrrolidine dyad demonstrated the existence of a photoinduced electron-transfer process that yields a radical ion pair with a lifetime three times longer than that obtained for the analogous C₆₀ dyad.

A series of donor–acceptor arrays (exTTF–oPPE–C₆₀) containing π-conjugated oligo(phenyleneethynylene) wires (oPPE) of different length between π-extended tetrathiafulvalene (exTTF) as electron donor and fullerene (C₆₀) as electron acceptor has been prepared by following a convergent synthesis. The key reaction in these approaches is the bromo–iodo selectivity of the Hagihara–Sonogashira reaction and the deprotecting of acetylenes with different silyl groups to afford the corresponding donor–acceptor conjugates in moderate yields. The electronic interactions between the three electroactive species were determined by using UV-visible spectroscopy and cyclic voltammetry. Our studies clearly confirm that, although the C₆₀ units are connected to the exTTF donor through π-conjugated oPPE frameworks, no significant electronic interactions are observed in the ground state. Theoretical calculations predict how a simple exchange from CC double bonds (i.e., oligo(p-phenylenevinylene) to CC triple bonds (i.e., oPPE) in the electron donor–acceptor conjugates considerably alters long-range electron transfer. Photoexcitation of exTTF–oPPE–C₆₀ leads to the following features: a transient photoproduct with maxima at 660 and 1000 nm, which are unambiguously attributed to the photolytically generated radical-ion-pair state, [exTTF^.+–oPPE–C₆₀^.−]. Both charge-separation and charge-recombination processes give rise to a molecular-wire behaviour of the oPPE moiety with an attenuation factor (β) of (0.2±0.05) Å⁻¹.

The photodynamics of a C₆₀–dithiapyrene donor–acceptor conjugate were compared with the corresponding C₆₀–pyrene conjugate. The photoinduced charge separation and subsequent charge recombination processes were examined by time-resolved fluorescence measurements on the picosecond timescale and transient absorption measurements on the picosecond and microsecond timescales with detection in the visible and near-infrared regions. We have observed quite long lifetimes (i.e., up to 1.01 ns) for the photogenerated charge-separated state in a C₆₀–dithiapyrene dyad without the need for i) a long spacer between the two moieties, or ii) a gain in aromaticity in the radical ion pair.