Picosecond transient infrared spectroscopy of 4-dimethylamino-4 '-nitrosilbene in the fingerprint region

A picosecond infrared spectrometer covering nearly the whole fingerprint re gion has been constructed. The infrared absorption spectrum of electronical ly excited 4-dimethylamino-4'-nitrostilbene, which has an intramolecular ch arge-transfer character, has been recorded. The observed infrared intensiti es are generally very strong (molar absorption coefficients as high as 3 x 10(3) mol(-1) dm(3) cm(-1)). The infrared spectral pattern of the excited s pecies is similar to that of the Raman spectrum. It is suggested that such features can be explained in terms of strong vibronic coupling in the obser ved excited species. Polarization measurements have also been performed.