Theoretical studies of one- and two-photon absorption properties for symmetric molecules based on bis(stilbene)diethylene

In order to investigate the substituting effects on the two-photon absorption (TPA) cross-section and the position of the TPA peak, the one- and two-photon absorption properties of a series of symmetric molecules with bis(stilbene)diethylene pi-conjugated bridge have been studied using ZINDO-SOS method. The transition moments from the ground state to the lowest excited state (M-ok) and from the lowest excited state to the TPA final state (M-kn), together with the detuning energy Delta E = E-ok - E-kn/2, were calculated using the INDO1 method included in the ZINDO program. The results indicate that bis-donor and bis-acceptor substitutions mainly affect the transition dipole moments M-ok and M-kn, and that donor or acceptor side groups have a strong influence on the detuning energy. Meanwhile, it was found that the molecules with the bis-donor structure possess enhanced TPA cross sections, and the molecules with cyano or methoxy side groups have a large red-shift with respect to molecules without side groups.