Knowledge Bank

Fluorescence lifetimes of the electronic origin and some higher vibronic bands of dibenzofuran (DBF) }, (2006), 244302.} and dibenzothiophene (DBT) have been determined from the analyses of their rotationally resolved S$1\leftarrow$S$0$ fluorescence excitation spectra in the gas phase. A decrease by a factor of eight in the fluorescence lifetime has been observed for DBT with respect to DBF, where presumably the heavy atom effect plays a significant role in the intersystem crossing mechanism of these heterocycles. The high resolution spectra of the electronic origin transitions of two non-concatenated furan derivatives, 2,5-diphenylfuran (DPF) and 2,5-diphenyl-1,3,4-oxadioxole (DPO), exhibit similar lifetime broadening, about four times greater than that of DBF. Detailed information about radiationless transitions in the "statistical" limit will be discussed.