Increasing the lifetimes of charge separated states in porphyrin–fullerene polyads

Abstract

Two linear polyads were designed using zinc(II)porphyrin, [ZnP], and N-methyl-2-phenyl-3,4-fullero-pyrrolidine (C₆₀) where C₆₀ is dangling either at the terminal position of [ZnP]–C₆H₄––C₆H₄–[ZnP]–C₆₀ (1) or at the central position of [ZnP]–C₆H₄––C₆H₄–[ZnP(C₆₀)]–C₆H₄––C₆H₄–[ZnP] (2) in order to test whether the fact of having one or two side electron donors influences the rate of electron transfer, k_et. These polyads were studied using cyclic voltammograms, DFT computations, steady state and time-resolved fluorescence spectroscopy, and femtosecond transient absorption spectroscopy (fs-TAS). Photo-induced electron transfer confirmed by the detection of the charge separated state [ZnP˙⁺]/C₆₀˙⁻ from fs-TAS occurs with rates (k_et) of 3–4 × 10¹⁰ s⁻¹ whereas the charge recombinations (CRs) are found to produce the [ZnP] ground state via two pathways (central [ZnP˙⁺]/C₆₀˙⁻ (ps) and terminal central [ZnP˙⁺]/C₆₀˙⁻ (ns) producing [¹ZnP] (ground state) and [³ZnP*]). The formation of the T₁ species is more predominant for 2.