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An approach to derive the steady-state fluorescence spectra of species in excited-state reactions is described. Such spectra we call species-associated spectra, SAS. Two algorithms are given to derive SAS: a simple approach, which might be used in many studies, and a general approach to be used when the overlap of the spectra of the individual excited species is annoying. Experimentally, single-photon-counting data were globally deconvoluted to generate time-resolved emission spectra and decay associated spectra, from which the species associated spectra were obtained. SAS were calculated for l,2-bis(10-acetoxy-9-anthryl)ethane (DADAE) in toluene at 21.0 °C. It is shown that the photophysics of DADAE can be described by a three-state excited-state reaction involving intramolecular excimer formation and also that the ground state shows heterogeneity. Also, studies of a mixture of POPOP, anthracene, and diphenylanthracene in ethanol (ground-state heterogeneity) have been included, as well as a study of /3-naphthol in water at pH 3.0. Computer-simulated two-state and three-state excited-state reactions have been included for comparison and for critical tests of the proposed algorithms.

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