Photoinduced electron transfer of zinc porphyrin-oligo(thienylenevinylene)-fullerene[60] triads; thienylenevinylenes as efficient molecular wires

Two novel donor-bridge-acceptor arrays (ZnP-nTV-C-60) with zinc porphyrin (ZnP) and fullerene (C-60), covalently connected by oligo(thienylenevinylene) (nTV) molecular wires (n = 3 and 8; 1a, b), have been prepared in a multistep convergent manner. The influence of the nTV-length on the electrochemical and electronic properties of the ZnP-nTV-C-60 triads has been revealed. Interestingly, an efficient photoinduced electron transfer process occurs in both triads with formation of intermediate radical-ion pairs (namely, ZnP center dot+-nTV-C-60(center dot-) and ZnP-nTV(center dot+)-C-60(center dot-)) as confirmed by the nanosecond transient absorption measurements in the visible and NIR regions. In polar and nonpolar solvents, the rate constants of charge-separation processes (k(CS)) via (ZnP)-Zn-1*-nTV-C-60 were found to decrease from ca. 1.2 x 10(10) s(-1) for n = 3 (RDA = 20 angstrom) to (5-7) x 10(9) s(-1) for n = 8 (R-DA = 60 angstrom) on the basis of fluorescence lifetime measurements of the ZnP moiety. From these data, together with those previously obtained ones for n = 4 in the related ZnP-nTV-C60 systems, a low attenuation coefficient was evaluated for the nTV molecular wires.