Knowledge Bank

Two aromatic CN-containing derivatives, p-tolunitrile and 9-cyano-10-methylanthracene, have been studied in a supersonic jet by fluorescence excitation and dispersed fluorescence spectroscopy. In p-tolunitrile we observe dual luminescene consisting of sharp vibrational structure near the excitation wavelength and congested or broadened structure at longer wavelengths. The sharp structure is more intense with excitation at the origin, while the red-shifted emission becomes relatively more intense when higher vibrational levels are excited. The results will be discussed in the terms of the charge transfer character of lowest electronic states. The torsional motion of the methyl group in 9-cyano-10-methylanthracene has been studied. A long progression in the spectrum indicates that there is a change in geometry upon $S1\leftarrow S0$ excitation. The main progression shows a $3-5cm-1$ splitting which may be due to the methyl torsional vibration. The effect of the CN substituent on the methyl torsion will be discussed.