Theoretically predicted influence of donors and acceptors on quadratic hyperpolarizabilities in conjugated long-chain molecules

The influence of the substitution positions of donors and acceptors on quadratic hyperpolarizabilities (β) was simulated by the AM1 method using four types of conjugated long-chain molecules having polydiacetylene structures. The chain-length dependences of β are greatly affected by the molecular type. The molecule, in which donor-donor pairs and acceptor-acceptor pairs alternately appear in the chain, has a narrow energy gap of about 1.6 eV and an exceptionally large β per 10 Å chain length, about 110 times larger than β of 2-methyl-4-nitroaniline.