The phosphorescence excitation spectrum of jet-cooled 4-H-1-benzopyrane-4-thione Original Research Article

The phosphorescence excitation spectrum of isolated 4-H-1-benzopyrane-4-thione molecules (BPT) in a pulsed supersonic jet was investigated by direct excitation of the first excited triplet state, S0 → T1. The electronic origin at 15828 cm−1 is assigned to the transition S0,0 → T1z,0, the transition S0,0 ⇌ T1(xy),0 is too weak to be detected with this method. The triplet lifetime τT1z,0 ≈ 11 μs is compatible with extrapolated values for BPT in dilute solutions. Vibronic transitions S0,0 → T1z,v were measured up to ∼ 1940 cm−1 above the origin; the vibrational structure of T1 was compared with the vibrational structure of S2. S0,0 → S1,v absorptions were not observed in the laser-induced phosphorescence experiment. Hot bands were observed under specific experimental conditions.