Light harvesting subphthalocyanine-ferrocene dyads: Fast electron transfer process studied by femtosecond laser photolysis

Ferrocene-subphthalocyanine dyads characterized, where ferrocene is axially linked with subphthalocyanine at its axial position with the B-O bond through the para and metapositions, namely Fc-pPhO-SubPc (dyad 1) and Fc-mPhO-SubPc (dyad 2). The geometric and electronic structures of 1 and 2 were probed by ab initio B3LYP/6-311G methods. The optimized structures showed that the Fc and SubPc entities are separated by 8.42 and 7.40 Å for dyads 1 and2, respectively. The distribution of the highest occupied frontier molecular orbital (HOMO) was found to be located on the Fc entity, while the lowest unoccupied molecular orbital (LUMO) was located on the SubPc entity, suggesting that the charge-separated states of the are Fc+-SubPc•-. Upon photoexcitation at the subphthalocyanine unit, both dyads undergo photoinduced electron transfer to form the corresponding charge-separated species, Fc⁺-SubPc•-. Based on their redox potentials determined by cyclic voltammetry technique, the direction of the charge separation and the energies of these states have been revealed. Femtosecond transient spectroscopic studies have revealed that a fast charge separation of 8.8 × 10¹⁰ and 1.2 × 10¹¹ s^-1 for 1 and 2, respectively, indicating fast charge separation in these simple dyads.