Conformations and electronic structures of dibenzylideneacetone

Abstract

The u.v. absorption spectra of dibenzylideneacetone (DBA) have been measured in various media (cyclohexane, ethanol, ethanol–methanol, and a polyethylene matrix) at room temperature and at 101 K. The results (and those calculated by the PPP method) indicate that DBA assumes a twisted cis,cis-conformation at room temperature in the polyethylene matrix, and a near planar one at low temperature. The torsion angles around the two single bonds between the olefin and the carbonyl group are estimated to be about 22° at room temperature. The effects of light irradiation on the structure of DBA have also been examined. The polarization of each band in the polarized absorption spectrum has been ascertained: e.g. the first πâ†�π band of the planar cis,cis-conformer at 351 nm is polarized along the long molecular axis. MINDO/2 calculations have also been performed to elucidate the equilibrium conformations for the free molecule.