Analysis of factors affecting luminescence decays: Concentration distribution of excited molecules in the reaction cell

An explicit method for calculating the spatial distribution of excited species in the reaction cell is presented. This method is used to analyze the relation between experimental conditions (excitation wavelength, ground state concentration, and laser intensity) and the observed luminescence decays (and the corresponding reaction kinetics) in both transient emission and transient absorption pulse laser photolysis experiments. Subsequently, the analysis was applied to the experimental conditions of previously extensively studied pyrene excimer formation in cyclohexane (J.B. Birks, Photophysics of Aromatic Molecules, Wiley-Interscience, London, 1970) and significantly different data were obtained in the redesigned experiment; the excimer formation and decay rate constants at 23.5 °C were found to be (4.77±0.04)×109 M−1 s−1 and (2.07±0.01)×107 s−1, respectively. Most importantly, the excimer dissociation into a singlet excited pyrene and ground state pyrene was found to be negligible, which is an important result that crucially affects the data processing in many previous and current applications of excimer formation.