Time- and wavelength-resolved delayed-fluorescence emission from acridine yellow in an inhomogeneous saccharide glass

Multiwavelength time-resolved spectroscopy is employed to study the triplet-state photophysics of acridine yellow dissolved in a rigid saccharide glass. Activated reverse intersystem crossing from photoexcited triplet states to the fluorescent singlet state provides a temperature-dependent decay pathway of the triplet population. While a unimolecular relaxation of a homogeneous excited triplet population would result in single-exponential decay off the delayed-fluorescence intensity, nonexponential decay was observed at all temperatures. Multidimensional regression analysis of time- and wavelength-resolved fluorescence and phosphorescence emission is found to be a powerful method to investigate triplet-state photophysics in an inhomogeneous matrix, where two discrete populations of acridine yellow excited states are found. From the temperature dependence of their decay rates, the energy barriers to activated decay of die triplet state are determined and compared to the triplet-singlet energy gaps determined spectroscopically from the component fluorescence- and phosphorescence-band origins.