THE RESONANCE-ENHANCED MULTIPHOTON EXCITATION SPECTRUM OF JET-COOLED 4-H-1-BENZOPYRANE-4-THIONE

The multiphoton (one-colour) excitation spectrum of jet-cooled 4-H-1-b enzopyrane-4-thione (BPT) is investigated in the wavelength region fro m 570 to 640 nm. The emission from BPT after multiphoton excitation wa s detected in two wide ranges in the blue (approximate to 400-500 nm) and the near UV (approximate to 250-400 nm). Resonance-enhanced excita tion via the first excited triplet state S-0-->T-1-->Psi(S,T)(') and t he first excited singlet state S-0-->S-1-->Psi(S,T)('') is observed. T he time dependence of the luminescence shows two components: (i) a fas t decay component (tau(f) < 50 ns), whose main part is assigned to S-2 -->S-0 fluorescence after two-photon excitation; (ii) a slow component (tau(f) approximate to 2 mu s) which may be attributed to the emissio n from a photofragment (CS), efficiently created in a metastable trip let state by a four-photon absorption.