The resonance-enhanced multiphoton excitation spectrum of jet-cooled 4-H-1-benzopyrene-4-thione

The multiphoton (one-colour) excitation spectrum of jet-cooled 4-H-1-benzopyrane-4-thione (BPT) is investigated in the wavelength region from 570 to 640 nm. The emission from BPT after multiphoton excitation was detected in two wide ranges in the blue (≈ 400–500 nm) and the near UV (≈ 250–400 nm). Resonance-enhanced excitation via the first excited triplet state S0 → T1 → ψ′S,T is observed. The time dependence of the luminescence shows two components: (i) a fast decay component (τf < 50 ns), whose main part is assigned to S2 → S0 fluorescence after two-photon excitation; (ii) a slow component (τs ≈ 2 μs) which may be attributed to the emission from a photofragment (CS∗), efficiently created in a metastable triplet state by a four-photon absorption.