Evidence of dynamical Jahn-Teller effect on triphenylene radical cation: Resonance Raman spectrum and ab initio quantum-chemical calculations

We report resonance Raman spectrum of the triphenylene radical cation generated by gamma -irradiation in a Freon glass at 77 K. Raman spectra were obtained using excitation in resonance with the strong cation absorption band near 400 nm. Ab initio calculations (Hartree-Fock, B-LYP, and B3-LYP, all with 6-31G basis set) were performed to obtain the equilibrium structures and vibrational force fields of triphenylene neutral and radical cation species. In addition, semiempirical calculations were carried out to identify the state in resonance with the excitation light and to simulate the vibronic structure of the resonance Raman spectrum. From these experimental and theoretical results, it is concluded that the bands observed in the resonance Raman spectrum of the radical cation contain the signatures of the Jahn-Teller effect on the cation which, similarly to benzene cation, is dynamical in nature.