Resolution of benzophenone delayed fluorescence and phosphorescence with compensation for thermal broadening

Principal component analysis with self-modeling based on the van't Hoff equation constraint was applied to a set of benzophenone luminescence spectra from degassed carbon tetrachloride solutions in the 14.7-88.5 degreesC range. This analysis differs from an earlier treatment in that it was preceded by compensation of the spectra for differential broadening with increasing T. A set of Gaussians was derived as previously described [Saltiel, J.; Sears, D. F., Jr.; Turek, A. M. J. Phys. Chem. A 2001, 105, 7569-7578] that, on convolution with the spectrum for each corresponding T, creates a uniformly broadened spectral set. Significant improvements in the accuracy of the resolved delayed fluorescence and phosphorescence spectra lead to a reliable comparison between prompt and delayed fluorescence spectra that confirms the conclusion that the short S, lifetime prevents full relaxation of emitting benzophenone singlets. The enthalpy difference for the T-1/S-1 equilibrium, 5.50 +/- 0.06 kcal/mol, agrees with the energy difference between the 0-0 bands of the resolved spectra, and the entropy difference is predicted nearly exactly by the difference in multiplicity between the two states (-R In 3 = -2.18 eu).