Integrating photoconversion building blocks with catalysts for solar fuels formation

We will report on electron transfer dynamics in several photodriven charge separation systems covalently-linked at fixed distances to catalysts for solar fuels formation. For example, the synthesis and spectroscopic characterization of a naphthalene-4,5-dicarboximide-1,8-dithiolate diiron complex (NMI-Fe₂S₂(CO)₆, 1) and a covalently-linked, fixed-distance zinc 5,10,15-tri-n-pentyl-20-phenylporphyrin-NMI-Fe₂S₂(CO)₆ donor-acceptor dyad (2) will be discussed. The electron-withdrawing nature of the NMI group makes the diiron complex among the most easily reduced hydrogenase mimics (-0.74 V vs. SCE) reported to date. Selective photoexcitation of the Zn porphyrin in 2 with 553 nm, 110-fs laser pulses yields transient absorption spectra in CH₂Cl₂ that show a distinct peak at 616 nm, which is assigned to (NMI-Fe₂S₂(CO)₆)^-• based on spectroelectrochemical measurements on 1, and is used to monitor the charge separation (CS) and charge recombination (CR) dynamics of 2.