Room Temperature Phosphorescence of 5,6-Benzoquinoline.

Phosphorescence emission of 5,6-Benzoquinoline embedded in poly (vinyl alcohol) film has been studied at room temperature. A strong green long-lived emission was observed in films doped with 5,6-Benzoquinoline while illuminated on a UV plate. A broad phosphorescence emission spectrum is centered at about 500 nm. The phosphorescence excitation spectrum follows the absorption spectrum of 5,6-Benzoquinoline, except for a long-wavelength part, which is well beyond the absorption band. This long-wavelength part of the absorption spectrum is responsible for the forbidden S0 - T1 transition. The excitation at 430 nm resulted in the long-lived emission with a spectrum similar to the phosphorescence spectrum obtained with UV excitation within the absorption of 5,6-Benzoquinoline. The phosphorescence anisotropy obtained with a direct S0 - T1 excitation is positive, while the UV excitation is negative. In contrast to fluorescence, the phosphorescence intensity strongly depends on temperature. Phosphorescence lifetimes with UV and long-wavelength excitation are similar, with a mean value of about 0.5 s.