Self-Consistent HMO Theory for the Excited State of Conjugated Molecules –Molecular Geometry, Molecular Vibration and Optical Spectra–

Abstract

The self-consistent HMO theory is applied to the excited state of conjugated molecules with a small modification of an electron-electron correlation term. The calculated wavelengths of the fluorescence are considerably in good agreement with the experimental values except for some carotenoids. It is found that the Stokes shift is almost constant among aromatic molecules and among carotenoids. The origin of this property is qualitatively discussed. A simple method for the calculation of optical spectral curves of large conjugated molecules is proposed. Applying it to all-trans β-carotene, we find that the calculated absorption curves are in good agreement with the experimental data and are appreciably different from mirror images of the calculated fluorescence curves. The vibrational frequencies and the normal coordinates of the molecular vibration are considerably different between the ground and the excited states in many modes.