Highly Varying Photophysical Properties of Thiocarbonyls: Validation of Fundamental Theoretical Concepts of Electronic Radiationless Transitions

摘要

A homologous series of gas-phase thiocarbonyl compounds displays highly variable photophysical properties. Thus, while thioformaldehyde, H_2CS, and thiocyclopentanone, H_8C_5S, exhibit fluorescence as well as phosphorescence, thiophosgene, Cl_2CS, displays fluorescence but not phosphorescence, and thiocyclobutanone, H_6C_4S, exhibits neither fluorescence nor phosphorescence. We show here that the very different emission characteristics of the four closely related thiocarbonyls can be rationalized on the basis of the presence or absence of the promoting mode for S_1 → S_0 internal conversion and the extent of S_1 and T_1 nonplanarity at the thiocarbonyl center.