New Electronic Transition of Ovalene in Solid para -H ₂ : The S ₁ –S ₀ Transition with Its Origin at 19 400 cm –¹

As part of our ongoing efforts to evaluate solid para-H₂ as a matrix host for electronic spectroscopy and to explore its potential in identifying carriers of the diffuse interstellar bands (DIBs), we previously reported the electronic spectrum of ovalene (C₃₂H₁₄), a medium-sized planar PAH with D2h symmetry, in solid para-H₂ and reassigned the previously reported S₁-S₀ spectral features to the S₂-S₀ transition with a lifetime of ∼1.7 μs (Weber, I., J. Phys. Chem. Lett. 2024, 15, 10696). Extending our investigation to lower energies, we now report a second set of spectral features, previously unobserved, with a prominent origin band at ∼19 400 cm⁻¹ in solid para-H₂, approximately 1650 cm⁻¹ below the previously reported S₂-S₀ origin at 21 050 cm⁻¹, and a short fluorescence lifetime of ∼10 ns. We assigned these new features to the S₁-S₀ transition based on quantum-chemical calculations at the TD-B3LYP-D3BJ/6-311++G(2d,2p) level and Franck-Condon Herzberg-Teller simulations.