Picosecond Transient InfraredSpectroscopy of 4-Dimethylamino-4′-Nitrostilbene in the FingerprintRegion

A picosecond infrared spectrometer covering nearly the whole fingerprint region has been constructed. The infrared absorption spectrum of electronically excited 4- dimethylamino-4′-nitrostilbene, which has an intramolecular charge-transfer character, has been recorded. The observed infrared intensities are generally very strong (molar absorption coefficients as high as 3×103 mol-1 dm3 cm-1). The infrared spectral pattern of the excited species 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 observed excited species. Polarization measurements have also been performed.