Knowledge Bank

Simultaneous measurments of absorption and fluorescence in a pulsed planar supersonic jet were used to determine fluorescence quantum yields of several vibronic levels in the $S2$ electronic manifolds of azulene, guiazulene, and 4,6,8-trimethylazulene. The quantum yields at the spectroscopic origins agreed well with those measured in low-temperature matrices, with the alkyl derivatives having smaller quantum yields than the parent hydrocarbon. However, several interesting new results were obtained in the study of higher-lying single vibronic levels. In azulene, mode-specific behavior was more prominent than in previous static gas studies. Vibronic coupling theory was used to estimate radiative rates for the levels excited, allowing us to infer rate constants for internal conversion as a function of excess vibrational energy.