Resolution of multiexponential spectral relaxation of Y_t-base by global analysis of collisionally quenched samples

We measured the wavelength-dependent intensity decays of 4,9-dihydro-4,6-dimethyl-9-oxo-1H-imidazo-1,2a-purine (Y_t-base) in propanol to determine the time-resolved emission spectra and rates of spectral relaxation. We found that resolution of the spectral relaxation times was dramatically improved by global analysis of the frequency-domain data with increasing amounts of the collisional quencher CCl₄. Collisional quenching preferentially decreases the longer-lived relaxed component of the emission, thereby increasing the fractional contribution of the incompletely relaxed portion of the emission. The data could not be explained by a single spectral relaxation time, and at least two relaxation times are needed to describe the time-dependent emission center of gravity of Y_t-base.