Intramolecular multiple Rehm–Weller plots in photoinduced electron transfer: competition between π- and n-type donor sites in benzylamines

Abstract

Earlier PET work has suggested that, for a given electron acceptor, distinct π- and n-type electron donors lead to distinct Rehm–Weller plots due to different Coulomb terms (C-terms) C_π and C_n, respectively. We studied benzylamine donors which embody both types of donor site. The results support the key role of the C-term in determining electron transfer efficiencies. A thorough evaluation of the adiabatic ionization potential (IP_a) of the π- and the n-moiety, serving as a measure of the corresponding relative oxidation potential (E_ox), was crucial to arrive at these findings. Hence, for an electron donor embodying more than one donor site the observable PET rate constant is not necessarily related to the easiest oxidizable site, i.e. to E_ox. This does not apply to photoinduced charge shift as here the C-term does not contribute to the driving force. Earlier useful correlations between E_ox and IP_a for π- and n-donors were updated.