Photophysics of 2,6-dimethyl-4H-pyran-4-thione in the vapor phase

Emission and excitation spectra of 2,6-dimethyl-4H-pyran-4-thione (DPT) vapor have been measured at different buffer gas pressures from 0 to 300 Torr and at different temperatures. Emission property of DPT vapor is found to vary significantly depending on pressure, excitation energy and temperature. The quantum yields of S1 fluorescence (ΦF1) and T1 phosphorescence (ΦP) increase with increasing buffer gas pressure and with decreasing temperature, while that of the S2 fluorescence (ΦF2) is almost unchanged. The values for ΦP and ΦF1 decrease almost exponentially with increasing excitation energy at low pressure, although the decrease of ΦF2 is not so significant compared to ΦF1 and ΦP. These observations have been interpreted in terms of the relaxation model involving the fast S2 → S1 internal conversion followed by the fast S1 → T1 intersystem crossing and the vibrational relaxation in the T1 manifold along with the temperature dependent nonradiative process from T1.