QUANTUM-CHEMICAL CALCULATION OF GEOMETRY, VIBRATION SPECTRUM, ABSORPTION AND EMISSION-SPECTRUM OF P-CYANO-P'-METHYL THIODIPHENYLACETYLENE

The geometry of the ground state and the first excited state of p-cyano-p'-methylthiodiphenylacetylene is optimized with the semi-empirical AM1 method. The geometry of the ground state is almost planar and the pi system is delocalized over the whole molecule. The geometry of the excited state is twisted, the two phenyl rings are perpendicular and the pi orbitals are now localized on the two phenyl rings. The absorption and emission spectra are calculated using a self-consistent reaction field method. The Stokes shift in acetonitrile solution was calculated to be 8220 cm-1 compared to the experimental Stokes shift of 8145 cm-1. The calculations indicate that the excited state is a twisted intramolecular charge transfer state (TICT) and that the emission in acetonitrile does occur from the TICT state.