Substructures and different energy relaxation time within the first electronic transition of pinacyanol

The S0-S1 absorption band substructure of pinacyanol dissolved in ethanol has been investigated with nonlinear polarisation spectroscopy in the frequency domain (NLPF). The evaluation of the experimental results has been done in the frame of global analysis for a set of four NLPF spectra at two test wavelengths. Four bands with maxima located at 520, 556, 565 and 607 nm have been identified. The energy relaxation after excitation in the 565 nm band is slower (T1 = 13 ps) than in the red-most band (T1 = 7 ps). This behaviour, inverse to usual excess-energy relaxation of organic molecules, suggests that these subbands belong to different isomers of pinacyanol.