Theoretical CD spectrum evaluation of the indolylfulgide molecules by using semi-empirical molecular orbital calculations

A fulgide is a photochromic molecule which can not be isomerized by a therm al reaction. The CD spectra of the optically resolved helically chiral indo lylfulgide (99% enantiomer excess), whose absolute configurations have been determined by an X-ray crystallographic analysis of their binaphthyl deriv ative, were estimated theoretically within the framework of semi-empirical molecular-orbital calculations. The optical rotatory strength of the indoly lfulgide was calculated based on the Rosenfeld equation by using the optimi zed structures, conformational energies, and molecular orbitals. The estima ted CD spectra reproduced characteristic features, such as the peak shape a nd sign of the Cotton effect, quite well, though the accuracy of the calcul ated wavelengths for the individual CD peaks' maxima was fair.