X-RAY CRYSTAL-STRUCTURES, MOLECULAR MECHANICS CALCULATIONS, AND CALCULATIONS OF THE NONLINEAR POLARIZABILITIES (BETA AND GAMMA) OF DICYANOVINYLBENZENE AND ITS METHOXY DERIVATIVES, AND COMPARISON WITH EXPERIMENTAL VALUES OF BETA

X-ray single-crystal study, molecular mechanics calculations, and calc ulations of the static nonlinear polarizabilities (beta and gamma) wer e performed for dicyanovinylbenzene and series of its mono- and dimeth oxy-substituted derivatives. X-ray analysis has been done for dicyanov inylbenzene, its o- and p-methoxy- and 2,4-dimethoxy-substituted deriv atives together with corresponding EFISH measurements of the beta valu es for these compounds. Nonlinear polarizabilities were calculated for all series of the mono- and disubstituted methoxy derivatives of the parent compound with modified finite-field formalism that included cal culation of polarization values versus static electric fields using se miempirical Hamiltonian, polynomial fit of all tensor elements of beta and gamma on the former data, and evaluation of the numerical instabi lity of the calculations. All calculations were performed with optimiz ed molecular geometries taken from X-ray data, molecular mechanics, nb initio, and semiempirical quantum chemical results. Good correlation was found between the predicted static and experimental molecular valu es of beta. A factor of 2.0 was found to be a probable adjustment para meter to account for the solvent (1,4-dioxane) and dispersion (at 1064 nm) effects. Crystal packing analysis of the X-ray structures studied together with energetic calculations revealed the factors responsible for formation of centrosymmetric crystals. Only o-methoxydicyanovinyl benzene (also known as DIVA) forms acentric crystals (space group P2(1 )) among the experimentally studied compounds, and it was found that i ts molecular dipole moment orientation with respect to the polar cryst al axis is close to the ''optimal'' for a manifestation of the high NL O responses.