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

• Published in: Chemical physics letters Vol. 501; no. 4-6; pp. 278 - 282
• Main Authors: Szmytkowski, Jędrzej, Brunet, Sophie M.K., Tripathy, Umakanta, O’Brien, Jaclyn A., Paige, Matthew F., Steer, Ronald P.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 07-01-2011
• ISSN: 0009-2614; 1873-4448
• DOI: 10.1016/j.cplett.2010.11.010

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► Both the S1 and S2 states of water-soluble ZnTPPS4− are quenched by iodide ion. ► An intermolecular electron-transfer mechanism is involved. ► For S1 the quenching is diffusion limited at constant ionic strength. ► For S2, static quenching occurs within a tight sphere of action.
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=1.75×109M−1s−1. The S2 state is quenched on a ps time scale by a static electron-transfer mechanism at an average donor–acceptor separation of 0.38nm. The implications of these data for dye-sensitized solar cells that employ I−/I3− as the redox medium are discussed.