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-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 and the first excited singlet state S₀ → S₁ → Ψ″_S,T is observed. The time dependence of the luminescence shows two components: (i) a fast decay component (τ_f < 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.