Photodriving the activity of water-oxidation catalysts is a critical step toward generating fuel from sunlight. The design of a system with optimal energetics and kinetics requires a mechanistic understanding of the single-electron transfer events in catalyst activation. To this end, we report here the synthesis and photophysical characterization of two covalently bound chromophore-catalyst electron transfer dyads, in which the dyes are derivatives of the strong photooxidant perylene-3,4:9,10-bis(dicarboximide) (PDI) and the molecular catalyst is the Cp à IrðppyÞCl metal complex, where ppy ¼ 2-phenylpyridine. Photoexcitation of the PDI in each dyad results in reduction of the chromophore to PDI •− in less than 10 ps, a process that outcompetes any generation of 3à PDI by spin-orbit-induced intersystem crossing. Biexponential charge recombination largely to the PDI-Ir(III) ground state is suggestive of multiple populations of the PDI •− -IrðIVÞ ion-pair, whose relative abundance varies with solvent polarity. Electrochemical studies of the dyads show strong irreversible oxidation current similar to that seen for model catalysts, indicating that the catalytic integrity of the metal complex is maintained upon attachment to the high molecular weight photosensitizer.photoinduced electron transfer | solar fuels | ultrafast optical spectroscopy | water oxidation A rtificial photosynthetic systems for solar fuels generation must integrate the functions of light harvesting, charge separation, and catalysis, with water as the source of electrons for reductive fuel-forming chemistry (1-5). The design of a lightdriven water-splitting system based on molecular catalysts requires a fundamental understanding of the individual electron transfer steps involved in multielectron catalyst activation. To investigate the energetic and kinetic demands of coupling photodriven charge separation and catalysis, many research groups have studied the photophysical properties of covalently linked redox-active organic dyes and transition metal complexes (6-16). In several cases, electron transfer to or from the metal has been observed and characterized, though energy transfer and intersystem crossing to the chromophore triplet state can be significant competing processes. In this work, we use derivatives of perylene-3,4∶9,10-bis(dicarboximide) (PDI) linked to an iridium complex of the type Cp à IrðN-CÞX to demonstrate light-driven single-electron oxidation of a highly active molecular catalyst precursor for water oxidation.Derivatives of PDI are useful organic chromophores for solar device applications (5,17,18). Their high molar absorptivity, stability, low cost, ease of synthetic manipulation, and often advantageous self-assembly properties have led to their use in molecular electronics and a variety of solar energy conversion systems (19). For solar fuels applications, the mild reduction potentials of PDI derivatives make their excited states powerful photooxidants, though there are only a few literature examples in which 1à PDI is used to ...

Ruthenium-catalyzed C-H bond activation was used to directly attach phenethyl groups derived from styrene to positions ortho to the imide groups in a variety of rylene imides and diimides including naphthalene-1,8-dicarboximide (NMI), naphthalene-1,4:5,8-bis(dicarboximide) (NI), perylene-3,4-dicarboximide (PMI), perylene-3,4:9,10-bis(dicarboximide) (PDI), and terrylene-3,4:11,12-bis(dicarboximide) (TDI). The monoimides were dialkylated, while the diimides were tetraalkylated, with the exception of NI, which could only be dialkylated due to steric hindrance. The absorption, fluorescence, transient absorption spectra, and lowest excited singlet state lifetimes of these chromophores, with the exception of NI, are nearly identical to those of their unsubstituted parent chromophores. The reduction potentials of the dialkylated chromophores are approximately 100 mV more negative and oxidation potentials are approximately 40 mV less positive than those of the parent compounds, while the corresponding potentials of the tetraalkylated compounds are approximately 200 mV more negative and approximately 100 mV less positive than those of their parent compounds, respectively. Continuous wave electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) data on the radical anion of PDI reveals spin density on the perylene-core protons as well as on the beta-protons of the phenethyl groups. The phenethyl groups enhance the otherwise poor solubility of the bis(dicarboximide) chromophores and only weakly perturb the photophysical and redox properties of the parent molecules, rendering these derivatives and related molecules of significant interest to solar energy conversion.

CO) 6 ]. By incorporating a secondary electron donor, the lifetime of the reduced diironhydrogenase mimic was extended by a factor of >450. Studies of photochemical hydrogen evolution using 1 and 2 reveal that the hydrogen generation efficiency depends on the lifetime of the final charge separated state. The ability to execute a multi-electron proton-coupled electron transfer mechanism in a stepwise manner will allow us to investigate the structural and electronic requirements for each step aiding in overall system optimization. Thus, it is possible to use the same

Elucidation of photoinduced charge transfer behavior in organic dye/metal hybrids is important for developing photocatalytic systems for solar energy conversion. We report the synthesis and photophysical characterization of a perylene-3,4:9,10-bis(dicarboximide) (PDI)Àruthenium(II) complex, bis-PDI-2,2 0 -bipyridineRu(II)Cl 2 (CN t butyl) 2 , which has favorable energetics, ΔG CS ≈ À1.0 eV, for singlet electron transfer from the Ru complex to PDI. Time-resolved optical spectroscopy reveals that upon selective photoexcitation of PDI, ultrafast charge transfer (<150 fs) from the Ru complex to 1* PDI generates the Ru(III)ÀPDI À• ion pair. The resulting vibrationally hot Ru(III)ÀPDI À• ion pair exhibits fast relaxation (τ = 3.9 ps) and charge recombination (τ CR = 63 ps). Our experimental and computational (DFT and TDDFT) studies show that energy-preserving photodriven singlet electron transfer can dominate in properly designed organic dye/metal complexes, making them of particular interest for use in artificial photosynthetic systems for solar fuels formation.

Metal coordination was probed as a versatile approach for designing a novel electron donor/acceptor hybrid [PDIpy(4){Ru(CO)Pc}(4)] (1), in which four pyridines placed at the bay region of a perylenediimides (PDIpy(4)) 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 PDIpy(4). The most important thing to note in this context is that both the [Ru(CO)Pc] oxidation and the PDIpy(4) 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 PDIpy(4), 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.