Electric dipole flip in a quadrupolar molecule with broken symmetry upon excited state absorption.

The nature of the second excited state in a quadrupolar molecule of the A-D-A structure, where A and D are an electron acceptor and an electron donor, respectively, has been studied. The orthogonality condition of the wave functions requires that the direction of the molecular dipole moment arising due to the charge transfer symmetry breaking be opposite in the first and second excited states. The dipole moment flip leads to large reorganization energy of the solvent upon excited state absorption. The manifestations of dipole flip are discussed. The dependence of the energy gap on the solvent polarity is found. The symmetry breaking effect on the transition dipole moment suppression is calculated. The available experimental data confirm the main conclusions.