Remarkably Efficient Photocurrent Generation Based on a [60]Fullerene-Triosmium Cluster/Zn-Porphyrin/Boron-Dipyrrin Triad SAM

A new artificial photosynthetic triad array, a [60]fullerene-triosmium cluster/zinc-porphyrin/boron-dipyrrin complex (1, Os3C60/ZnP/Bodipy), has been prepared by decarbonylation of Os-3(CO)(8)(CN(CH2)(3)Si-(OEt3)(mu(3)-eta(2):eta(2):eta(2)-C-60) (6) with Me3NO/MeCN and subsequent reaction with the isocyanide ligand CNZnP/Bodipy (5) containing zinc porphyrin (ZnP) and boron dipyrrin (Bodipy) moieties. Triad 1 has been characterized by various spectroscopic methods (MS, NMR, IR, UV/Vis, photoluminescence, and transient absorption spectroscopy). The electrochemical properties of 1 in chlorobenzene (CB) have been examined by cyclic voltammetry; the general feature of the cyclic voltammogram of 1 is nine reversible one-electron redox couples, that is, the sum of those of 5 and 6. DFT has been applied to study the molecular and electronic structures of 1. On the basis of fluorescence-lifetime measurements and transient absorption spectroscopic data, 1 undergoes an efficient energy transfer from Bodipy to ZnP and a fast electron transfer from ZnP to C-60; the detailed kinetics involved in both events have been elucidated. The SAM of triad 1 (1/ITO; ITO=indium-tin oxide) has been prepared by immersion of an ITO electrode in a CB solution of 1 and diaza-bicyclo-octane (2:1 equiv), and characterized by UV/Vis absorption spectroscopy, water contact angle. X-ray photoelectron spectroscopy. and cyclic voltammetry. The photoelectrochemical properties of 1/ITO have been investigated by a standard three-electrode system in the presence of an ascorbic acid sacrificial electron donor. The quantum yield of the photoelectrochemical cell has been estimated to be 29% based on the number of photons absorbed by the chromophores. Our triad 1 is unique when compared to previously reported photoinduced electron-transfer arrays, in that C-60 is linked by pi bonding with little perturbation of the C-60 electron delocalization.