NEW CHIRAL BIS(DIPOLAR) 6,6'-DISUBSTITUTED BINAPHTHOL DERIVATIVES FOR2ND-ORDER NONLINEAR OPTICS

(S)everal chiral molecules with C-2 symmetry derived from two geometri es of the binaphthol (BN) system substituted with different accepters have been synthesized in order to study the possibility of producing n oncentrosymmetric crystals formed from these chiral structures. All th e molecules possess two equal donor-acceptor (D-A) systems linked toge ther to give a bis(dipolar) V-shaped system. The dihedral angle a betw een the two connected D-A sys tems has been controlled by chemical met hods; this leads to distinct changes in the optical spectra of the con nected D-A chromophores, primarily changes caused by effective conjuga tion of the D-A system imposed by conformation constraints. The crysta l structure of chiral -2,2'-diethoxy-1,1'-binaphthyl-6,6'-dicarbaldehy de (4 a) has been elucidated and indicates that the dipoles in the nap hthyl moiety within the overall noncentrosymmetric crystal can cancel out exactly despite the noncentrosymmetry. The crystal structure of ra cemic 9,14-dicyanodinaphtho[2,1-d:1',2'-f][1,3]-dioxepin (2b) was foun d to be centrosymmetric. The new compounds were investigated for secon d-harmonic generation (including BN derivatives reported earlier) by t he Kurtz-Perry powder test to evaluate the second-order nonlinear opti cal (NLO) properties of polycrystalline samples. Although chirality en sures noncentrosymmetric crystals, only modest (approximate to 2-methy l-4-nitroaniline) or no nonlinearities were observed in the powder tes t, For a representative selection of the molecules, the first molecula r hyperpolarizabilities beta(2) were shown to be very high (up to 888 x 10(-30) esu for 14a) by electric field induced second harmonic gener ation (EFISHG) measurements. Synthetic routes are reported for optical ly pure 6,6'-disubstituted-2,2'-diethoxy-1,1'-binaphthyls 2a, 3a, 6a, 10a, 11a, 14a, 15a [acceptor=CN, SO2CH3, (E)-CH=CHSO2CH3, (E)-CH-CH(p- PhCN), (E)-CH=CH(p-Ph-SO2CH3), (E)-CH=CH(p-PhCh=C-(CN)(2)), (E)-CH=CHC H=C(CN)(2)] and optically pure substituted-dinaphtho[2,1-d:1',2'-f][1, 3]dioxepins 2b, 3b, 10b, 11b, 13b, 14b, 15b [acceptor = CN (only racem ic), SO2CH3, (E)-CH=CH-(p-PhCN), (E)-CH=CH(p-PhSO2CH3), (E)-CH=CH(p-Ph NO2), (E)-CH=Ch-(p-PhCh=C(CN)(2)), (E)-CH=CH-CH=C(CN)(2)].