X-ray Crystal Structures, Molecular Mechanics Calculations, and Calculations of the Nonlinear Polarizabilities (β and γ) of Dicyanovinylbenzene and Its Methoxy Derivatives, and Comparison with Experimental Values of β

Abstract

X-ray single-crystal study, molecular mechanics calculations, and calculations of the static nonlinear polarizabilities (β and γ) were performed for dicyanovinylbenzene and series of its mono- and dimethoxy-substituted derivatives. X-ray analysis has been done for dicyanovinylbenzene, its o - and p -methoxy- and 2,4-dimethoxy-substituted derivatives together with corresponding EFISH measurements of the β values 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 calculation of polarization values versus static electric fields using semiempirical Hamiltonian, polynomial fit of all tensor elements of β and γ on the former data, and evaluation of the numerical instability of the calculations. All calculations were performed with optimized molecular geometries taken from X-ray data, molecular mechanics, ab initio, and semiempirical quantum chemical results. Good correlation was found between the predicted static and experimental molecular values of β. A factor of 2.0 was found to be a probable adjustment parameter 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 -methoxydicyanovinylbenzene (also known as DIVA) forms acentric crystals (space group P 2 1 ) among the experimentally studied compounds, and it was found that its molecular dipole moment orientation with respect to the polar crystal axis is close to the “optimal” for a manifestation of the high NLO responses.