A model Hamiltonian for examining the infrared intensities of charged conjugated π-electron systems: application to the triphenylene radical cation

A model Hamiltonian for examining the origin of the infrared intensities of charged conjugated π-electron systems is presented. With this model Hamiltonian, dipole derivatives are estimated from electric-field-induced changes in bond orders. As an example of the application of the model, dipole derivatives are calculated for the Jahn–Teller distorted structures of the triphenylene radical cation. It is shown that good estimates of the signs and magnitudes of the dipole derivatives of the CC stretches are obtained with the model Hamiltonian. The relation between the electronic structures and the signs of the dipole derivatives is discussed.