Spectroscopic characterization of 1,2,4,5-tetracyanobenzene

In this Letter, we characterize the vibrational levels of 1,2,4,5-tetracyanobenzene (TCNB) in the electronic ground and first excited states by dispersed fluorescence and laser induced fluorescence spectroscopy. The Franck–Condon activity was observed in the totally symmetric modes 6a, 9a, 1, and 7a. Few non-totally symmetric modes, like 16a and 10a, were also found to be active. The energy minimized structures and normal mode frequencies for TCNB both in the ground state and electronic excited state were calculated ab initio at various levels of theory using 6-31++G∗∗ basis set.