Fluorescence spectroscopy of C60 in toluene solutions at 5 K

We have recorded the dispersed fluorescence and the fluorescence excitation spectra of C₆₀ in toluene matrices at 5 K. Upon excitation with the green Ar⁺ laser line (λ=514 nm) we obtained for the first time in this matrix well resolved visible fluorescence spectra which we have compared with those observed in other low temperature matrices. Our spectra were interpreted and assigned using theoretical assessments of vibronic activities of transitions between the three lowest excited electronic states ¹T_1g, ¹T_2g, ¹G_g and the totally symmetric ground state, and on the basis of a single 0⁰ level which has pseudo-Jahn–Teller (JT) components of the three near-degenerate excited states. The fluorescence spectra exhibit prominent JT induced h_g(1) progressions, Herzberg–Teller-induced h_u and other ungerade mode vibrations, including a very active t_1u(4) mode. Excitation wavelength independent bands are assigned to the fluorescence of C₆₀ molecules in toluene microcrystals embedded in the toluene glass whereas excitation wavelength dependent features are interpreted as originating from C₆₀ molecules isolated in the toluene glass itself. These interpretations are supported by the results of spectrally selective detected fluorescence excitation spectra.