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 °C 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 1 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 ln 3 = −2.18 eu).