Fluorescence decays of 9,10-dichloroanthracene and its van der waals complexes with rare gas atoms in supersonic free jets

Abstract The fluorescence lifetimes of 9,10-dichloroanthracene (DCA) and its van der Waals complexes with Ar, Kr, and Xe atoms were measured in supersonic free jets. For bare DCA the origin of the S 1 state (S 1 (0)) shows a long lifetime of 24.8 ns while the 403 cm −1 band undergoes intersystem crossing (ISC) to a nearby triplet state (T n ) as implied by its shortened lifetime of 13.1 ns. The electronic origin of T n is located between S 1 (0) and 403 cm −1 levels. The fluorescence lifetime shows an oscillatory dependence o oscillatory behavior is discussed on the basis of the Franck-Condon factor between the S 1 vibrational level and the isoenergetic T n vibrational level in the sparse level structure. The electronic origins of the vdW complexes show long lifetimes, nearly the same as the bare DCA. The absence of the heavy atom effect on the ISC for the vdW complexes in a low E ν range is explained by a microscopic solvent shift and relaxation. The fluorescence decays of the vdW complexes with 1390 cm −1 or higher E ν become dramatically slow in comparison with those of the corresponding bare bands. It is suggested from a non-exponential fluorescence decay that the fragments DCA produced by vibrational predissociation are distributed into two or more vibrational levels. The fragment complexes DCA·Xe m produced from DCA·Xe n ( m ) also do not exhibit the heavy atom effect on the ISC.