Evidence for molecular distortion involving the carbonyl group in triplet states of carbonyl derivatives of naphthalene obtained from time resolved vibrational spectroscopic studies Original Research Article

The CO stretching vibration appears in the infrared spectra of 2-naphthaldehyde (1), 2-acetonaphthone (2), 2-naphthoic acid (3), methyl2-naphthaoate (4) and 1,2-dihydro-3H-benz[e]inden-3-one (5) in the state T1(ππ∗) between 1600 and 1700 cm−1. There is a strong line in the Raman spectrum of 1–5 in the state S0 arising from the CO stretching mode, but such a line is lacking in their resonance Raman spectra when they are in the state T1. This is attributed to a large amplitude out-of-plane twist of the CO group in 1–4 and to a pyramidalization of the C atom in the CO group of 5 in the equilibrium geometry of the state T1.