A transition-metal-assembled dyad containing a porphyrin module and an electro-deficient ruthenium complex

A porphyrin-ruthenium complex conjugate PH2-Ru has been constructed, the ruthenium-based component being a strong electron and energy acceptor. The porphyrin site can be metallated by zinc(II) to afford the dyad PZn-Ru. The electrochemical parameters of the reference compounds (components) and the two dyads have been determined, as well as the absorption and emission characteristics. These data allow us to predict the exergonicity of the photoinduced electron and energy transfer processes likely to take place in both dyads. Low temperature emission measurements clearly show that very fast energy transfer occurs in two steps in both dyads. The singlet excited state porphyrin is first quenched by the Ru component, leading to a Ru-complex localized triplet-excited state ((3)MLCT) which, in turn, transfers its triplet energy back to the porphyrin unit attached to it so as to generate the porphyrin triplet excited state.