NON A PRIORI ANALYSIS OF FLUORESCENCE DECAY SURFACES OF EXCITED-STATE PROCESSES .1. THEORY

Abstract

Fluorescence can be collected under a variety of experimental conditions. Simultaneous, or global, analysis of the constituent decay curves of a fluorescence decay surface can be performed by linking the common parameters in the various expressions used in the fitting process. Fluorescence decay surfaces can be globally analyzed in terms of the rate constants and species associated spectra by the so-called global compartmental analysis [Beechem et al. Chem. Phys. Lett. 1985, 120, 466]. Up to now, this method required that the decay curves be properly normalized and that the ratio of the absorbances of the species in the ground state be known. However, normalization between collected decay curves is not always feasible nor is knowledge of the ratio of the ground-state absorbances always available. It is demonstrated in this paper that the conditions of proper normalization and knowledge of the ratio of the absorbances are not required for the direct analysis of two-state excited-state intermolecular processes. The required combinations of experiments necessary to achieve the direct analysis can be summarized as follows: n(conc)n(em) greater-than-or-equal-to n(conc) + n(em), where n(conc) and n(em) denote the number of different concentrations and emission wavelengths, respectively. When the total concentration of the ground-state species and the total optical density are known, the equilibrium constant of the ground-state process and the extinction coefficients of the absorbing species can be determined from time-resolved fluorescence measurements.