Data analysis techniques for monitoring excited state kinetics

Progress in understanding photoinitiated reactions requires that kinetics of small dynamic populations of triplet state initiators and intermediates be distinguished from one another and from larger populations of precursor and solvent molecules. In this work, several approaches for analysis of multiwavelength data of photochemical reactions are described. The first addresses the analysis of time-resolved delayed-fluorescence and phosphorescence spectra of dye molecules in an inhomogeneous glassy matrix; a global analysis of the time- and wavelength-resolved emission data is used to resolve the spectra and kinetics of two discrete populations of molecules in the sample. The resolved kinetic parameters are then related to the wavelength dependence of the resolved spectra. A second application describes multidimensional least squares and factor analysis techniques for resolving transient Raman spectra of triplet state photoinitiators from Raman bands of the ground state and solvent. Raman spectra of solutions containing the ground-state photoinitiator and solvent are acquired using a series of laser pulses which simultaneously initiate and probe triplet state formation. The kinetics of optical excitation produce a higher order dependence on laser intensity for the triplet state permitting resolution of the component spectra.