Quantum Mechanical Consistent Force Field (QCFF/PI) Method: Calculations of Energies, Conformations and Vibronic Interactions of Ground and Excited States of Conjugated Molecules

The extension of the Consistent Force Field approach to π electron systems is outlined. The quantum mechanical energy of π electrons is given as an analytical function of the molecular coordinates. It is shown that with this analytical description one can calculate efficiently equilibrium geometries and vibrational frequencies of ground and excited states of conjugated molecules. Application of the calculated geometry and vibrations to the analysis of vibronic structure is described. A preliminary account of the use of observed vibronic structure for determination of the geometry of excited electronic states is given.