Mode- and complexation-specific singlet-triplet coupling in jet-cooled perylene studied by time-resolved fluorescence spectroscopy

Fluorescence spectral data for jet-cooled perylene indicate little or no vibrational coupling for most levels up to 1057 cm −1 . Fluorescence time profiles have been measured for several levels, and evidence presented for several cases of coupling to the triplet manifold. The principal Franck-Condon-active mode 353 1 exhibits a single-exponential decay, although the emission spectrum indicates little or no singlet vibrational level mixing. The (CH 4 ) 1 complex of perylene, also excited into 353 1 , exhibits a single-exponential profile with a fast decay, again indicating strong singlet-triplet coupling, while the 2 : 1 and 3 : 1 complexes at the same energy are strongly fluorescent. These results imply that singlet-triplet coupling is level-selective, and can be induced by complexation.