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

Abstract

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.