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

Two novel donor-bridge-acceptor arrays (ZnP-nTV-C₆₀) with zinc porphyrin (ZnP) and fullerene (C₆₀), 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-C₆₀ triads has been revealed. Interestingly, an efficient photoinduced electron transfer process occurs in both triads with formation of intermediate radical-ion pairs (namely, ZnP⁺-nTV-C₆₀^- and ZnP-nTV⁺-C₆₀^-) 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) via¹ZnP*-nTV-C₆₀ were found to decrease from ca. 1.2 × 10¹⁰ s^-1 for n = 3 (R _DA = 20 Å) to (5-7) × 10⁹ s^-1 for n = 8 (R_DA = 60 Å) 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.