MISSING-ORBITAL ANALYSIS ON HYPERPOLARIZABILITY-BETA OF ORGANIC-MOLECULES - ENHANCEMENT OF THE OFF-DIAGONAL COMPONENT BETA(ZXX) USING MULTIPLE SUBSTITUTIONS

The first-order hyperpolarizability components, beta(zzz) and beta(zzz ) for C-2v molecules (the z axis being the principal axis) are analyze d after simplified sum-over-states calculations. Compared with p-nitro aniline (PNA), beta(zzz) is three times enhanced by x-extended pi conj ugation realized by a bulky substrate in 9-amino-10-nitroanthracene (A NA) and by multiple substitutions in 1,5-diamino-2,4-dinitrobenzene (D DB). While ANA shows beta(zzz) unchanged because its z-directed charge transfer (CT) is similar to PNA, DDB has a beta(zzz) 1/3 of PNA, whic h is reduced by two weak CTs introduced by two ortho-positioned donor- acceptor pairs on both sides of the z axis.