Azulene Revisited: Picosecond Decay of the S₁ State in the Gas Phase and in Solution

In this paper we report the results of an experimental study of picosecond time‐resolved relaxation dynamics of the S₁ state of the azulene molecule in solution and in the low pressure gas phase, utilizing consecutive two‐photon excitation S₀ → S₁(v) → S₂ (or S₃), with the exciting and the monitoring picosecond pulses chosen at the same wavelength. The nonradiative electronic relaxation times for azulene in solution were τ_nr = 4 ± 3 ps for S(v = 5), excited at 530 nm, and τ_nr = 3 ± 2 ps for S(v = 2), excited at 625 nm, while for the “isolated” molecule case τ_nr = 4 ± 3 ps for S(v = 2), excited at 625 nm. The electronic relaxation rate of the S₁ manifold exhibits only a weak dependence on the excess vibrational energy E_v up to E_v = 4800 cm⁻¹. The electronic relaxation rate is practically unaffected by solvent perturbations, as appropriate for the statistical limit of intramolecular radiationless transitions.