Photophysics and halide quenching of Soret-excited ZnTPPS4− in aqueous media

Steady state S2–S0 and S1–S0 absorption and emission spectra and picosecond S2 decay and S1 fluorescence rise times have been measured for the model porphyrin ZnTPPS4− in water and in aqueous iodide solutions of constant ionic strength. The dynamics of S1 quenching by iodide are well-modeled by a Stern–Volmer mechanism yielding kQ = 1.75 × 109 M−1 s−1. The S2 state is quenched on a ps time scale by a static electron-transfer mechanism at an average donor–acceptor separation of 0.38 nm. The implications of these data for dye-sensitized solar cells that employ I−/I3− as the redox medium are discussed.