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 P21) 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.

Molecular Crystal Structures and Nonlinear Optical Properties in the Series of Dicyanovinylbenzene and Its Derivatives

“…To calculate important NLO molecular electronic characteristics (dipole moments and second-order polarizabilities β) we have used the technique described in detail in our previous paper. 17 It was shown that the values of β calculated with the experimental X-ray geometries, as well as obtained using quantum-chemical or molecular mechanics optimized geometry parameters, are very close in most cases. So, the easiest way to estimate a priori some molecular electronic properties for a large series of compounds is the molecular mechanics calculation of the optimal molecular geometry and semiempirical quantum-chemical calculation of their electronic properties.…”

“…In our previous paper 17 we reported X-ray crystal structures, molecular mechanics calculations, and calculations of the nonlinear polarizabilities (β and γ) for dicyanovinylbenzene and a series of some of its methoxy-substituted derivatives (with o-methoxy, p-methoxy, and 2,4-dimethoxy substituents). This class of organic chromophores represents an interest in NLO material studies because of the well-known efficiency of the -CHdC(CN) 2 group as an electron acceptor with an extended conjugation chain.…”

“…It was shown 17 that among the four compounds studied only o-methoxy-dicyanovinylbenzene, also known as DIVA, has an acentric crystal space group (P2 1 ) and therefore exhibits NLO properties in the solid state. 19,20 The corresponding parasubstituted derivative and 2,4-dimethoxy analogue (having much higher molecular second-order optical responses β) were found to form centrosymmetric crystal structures.…”

“…An additional purpose of the present publication is an estimation of the plausibility of the theoretical approach (described in detail in ref 17) for prediction of the possible centric/acentric packing arrays in crystals of the compounds of interest. This simple approach is based on calculations of the relative energies of the possible molecular dimers using molecular mechanics technique.…”

2-Amino derivatives of 5-nitrophenylacetamide

“…One such compound is the donor±acceptor substituted benzene derivative N-[2-(dimethylamino)-5-nitrophenyl]acetamide, (III), which crystallizes in a non-centrosymmetric space group and which therefore allows second-harmonic generation (Baumert et al, 1987;Norman et al, 1987). As a part of a search for new NLO materials (Antipin et al, 1997(Antipin et al, , 1998, we synthesized two new compounds, N-[2-(isopropylamino)-5-nitrophenyl]acetamide, (I), and N-[2-(butylamino)-5-nitrophenyl]acetamide, (II), which are analogous to (III). In this work we present the results of structural investigations of the compounds (I), (II) and (III).…”