ELECTRONIC PROPERTIES AND PHOTOCHEMICAL MONOMOLECULAR REACTIONS IN ORGANIC CONJUGATED COMPOUNDS: PHOTOCYCLIZATIONS, PHOTOISOMERIZATIONS AND PHOTOCHEMICAL REARRANGEMENTS—I

Abstract

Abstract— It is assumed that quantum yields of monomolecular reactions are mainly determined by the probability of de‐excitation from the excited state to the ground state of the photoproduct and that a reaction will occur only if the stable molecular configuration of the excited state is close enough the molecular configuration of the photoproduct. In order to evaluate the stabilizing deformation of the excited states, the different methods of representing the excited states wave‐functions are compared. Though very different in their ability to reproduce spin densities in the triplet state, these methods appear to give very close results for the electronic repartition; particularly, unrestricted Hartree‐Fock calculations seem to give nearly the same net charges and bond indices for corresponding singlet and triplet states. A simple method for a rough evaluation of the direction and of the amplitude of the stabilizing deformation is proposed. In the Hiickel scheme, the variations in bond orders may be taken as an approximate index of that deformation.