Spectroscopic study of 2-indanone: The T1 3(n,π*) and S1 1(n,π*) states

Abstract

Phosphorescence excitation and emission spectra of 2-indanone single crystal have been observed at 1.5 K. The lowest triplet state T1 is of π*←n character which is localized in the carbonyl moiety. The very weak 0–0 band is located at 28 853 cm−1. The molecule is pyramidally distorted like formaldehyde and has an active out-of-plane C=O wagging mode. The barrier height to inversion (V) and the C=O bend angle at the potential minimum (θm) have been determined to be 883 cm−1 and 37°, respectively. This distortion is consistent with the previous ODMR results. Fluorescence excitation spectrum of 2-indanone has also been observed using a pulsed supersonic nozzle beam technique. The lowest excited singlet state is also of π*←n character localized in the carbonyl moiety. The 0–0 band is relatively intense and located at 30 664 cm−1. We obtained V=1006 cm−1 and θm =37° for the S1 state. The spectroscopic results and ab initio calculation show that the S1 and T1 states of 2-indanone are very similar to those of cyclopentanone. The difference between the spectral features of the T1 and S1 transitions is explained by the symmetry lowering of the molecule and by the vibronic coupling with a higher excited state.