Measurement of quantum yields for photochemical systems interconverted by both light and heat

We present an analysis of the kinetics of photochemical reactions in which two molecules (or groups of molecules) are interconverted by light and one is thermally unstable, in the presence of arbitrary amounts of absorbance, for both stirred and transport-free media. We show that all photokinetic parameters can be determined in a single bleaching experiment that stops well short of achieving a steady state, regardless of the time scale of the reaction (provided it is a one-photon process). Explicit analytical formulas for the fitting of data to calculation, with error estimates, are provided, along with a discussion of implementation using common commercial software.