Temperature dependence of the emission spectra of p-benzoquinone in a p-dichlorobenzene matrix

Emission and excitation spectra of p-benzoquinone have been measured in a partially translucent p-dichlorobenzene host matrix at different temperatures from 77 up to 323 K. Successive occurrence of the T1(n,π⁎) and T2(n,π⁎) phosphorescence and S1(n,π⁎) fluorescence has been observed for p-benzoquinone upon increasing temperature. The S1–T2 and T2–T1 energy separations determined from the temperature dependence of the emission intensities agreed well with those obtained from the locations of the T1 and T2 phosphorescence and S1 fluorescence origins. Occurrence of the emission from S1 and T2 is brought by the thermal population from the T1 state. The symmetries of the T1 and T2 states were determined to be B1g and Au, respectively, based on the spectral data.