Circular dichroism of an optically active benzene chromophore-1-methylindan

Abstract

The gas phase circular dichroism and absorption spectra of a conformationally stable, optically active benzene chromophore, S‐(+)‐1‐methylindan, has been measured from 280 to 170 nm. The structure of the CD spectrum differs from that of the absorption in the B_1u region and this observation is interpreted as evidence for the presence of a σ−π* or π−σ* E_1g state in addition to the π−π* B_1u state. Also, the CD spectrum near 190 nm requires the conclusion that an additional electronic state is located between the analogs of the B_1u and E_1u states. This state is assigned as E_2g, in agreement with consistent theoretical predictions. The observed CD spectra can be accounted for in a consistent manner on the basis of a scheme which uses the results of parametrized calculations of coupled‐oscillator contributions and one‐electron term calculation results due to Caldwell and Kauzmann for the molecule studied.