Fluorescence excitation spectra, Raman spectra and structure of isochroman in its S1 (π, π∗) state

Abstract

The laser induced fluorescence excitation (FE) spectra of jet-cooled isochroman is used along with the theoretical calculations to assign vibronic levels in 0–500cm−1 region in the S1 (π, π∗) state. The origin of S0→S1 transition appears at 36,989cm−1. Six low-frequency vibrations are identified in the FE spectrum. These vibrations are compared to the corresponding levels in S0. The ab initio DFT calculations show the molecule to be in the twisted structure in both S0 and S1 states with a high barrier to planarity. This barrier is theoretically calculated to be 3572cm−1 in S0 with the twisting angle as 33° and the corresponding values in S1 are 3916cm−1 and 31°. Raman spectra are well corroborated by the theoretical calculations. TDDFT calculations are done on the optimized geometries and compared with the experimental results.