Large values of the static first(β) and second(γ) hyperpolarizabilities were obtained for donor-acceptor molecules having mixed bridges with mesoionic rings inserted between polyenic moieties. The magnitudes of β and γ were calculated at the AM1/TDHF semiempirical level. Donor(D)/acceptor(A) pairs of different strengths were used to test the potential of the new model bridges. The largest value was obtained by linking thedicyanomethylene(A) and phenylamine(D) at the opposite ends of mixed bridges.Unlike D/A molecules traditionally reported in the literature, the phenylamine was linked to the bridge by the nitrogen heteroatom. The effect of the nature and size of the bridge in the magnitude of the hyperpolarizabilities was investigated. The push-pull systems with the extended bridges, containing two mesoionic rings and polyenic moieties, present the larger magnitudes values of β and γ.The results show that the combination of the selectedbridges and D/Apairs can be responsible for very large hyperpolarizabilities.
β and γ hyperpolarizabilities; polyenic; donor-bridge-acceptor organic systems; AM1/TDHF methodology
