Quantum yield determinations for sub-nanosecond lived excited states and photoproducts. Applications to inorganic complexes and photosynthetic models

This paper presents a procedure for determining the quantum yields of nonluminescent excited states and photoproducts with subnanosecond lifetimes. The authors describe both a procedure for calibrating the intensity of the photoexcitation pulse (einstein cm/sup -2/ pulse/sup -1/) and a numerical calculation of percent excitation for an optically dense sample. Particular attention is paid to the case for which a large fraction of starting material is transformed into photoproduct, a common occurrence in picosecond absorption spectroscopy. As motivating applications, determined are the quantum yields of (1) the lowest energy ligand-field excited state of Fe(phen)/sub 3//sup 2 +/ (phen = 1,10-phenanthroline) and (2) the 200-ps-lived electron-transfer (ET) photoproduct (Mg/sup +/-H/sub 2//sup -/) in a diporphyrin model of photosystem II (PSII) to be 1.00 +/- 0.05 and 0.9 +/- 0.1, respectively. In both cases the observed photoproducts are formed from the decay of ultrashort-lived, initial excited states (tau < ps). 29 references, 4 figures.