Increasing the lifetimes of charge separated states in porphyrin-fullerene polyads.

Two linear polyads were designed using zinc(ii)porphyrin, [ZnP], and N-methyl-2-phenyl-3,4-fullero-pyrrolidine (C) where C is dangling either at the terminal position of [ZnP]-CH-[triple bond, length as m-dash]-CH-[ZnP]-C (1) or at the central position of [ZnP]-CH-[triple bond, length as m-dash]-CH-[ZnP(C)]-CH-[triple bond, length as m-dash]-CH-[ZnP] (2) in order to test whether the fact of having one or two side electron donors influences the rate of electron transfer, k. 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˙+]/C˙ from fs-TAS occurs with rates (k) of 3-4 × 10 s whereas the charge recombinations (CRs) are found to produce the [ZnP] ground state via two pathways (central [ZnP˙+]/C˙ (ps) and terminal central [ZnP˙+]/C˙ (ns) producing [1ZnP] (ground state) and [3ZnP*]). The formation of the T species is more predominant for 2.