Oleg Ya. Borbulevych

Experimental and theoretical study of the structure of N, N-dimethyl-4-nitroaniline derivatives as model compounds for non-linear optical organic materials

Abstract Molecular and crystal structure of a series of derivatives of N , N -dimethyl-4-nitroaniline has been studied by both X-ray diffraction method and high-level ab initio calculations. According to these data, the dimethylamino groups were found to have a trigonal-pyramidal configuration and are considerably turned with respect to the ring plane in all molecules having a substituent in the ortho -position; on the contrary, this group is planar in the meta -substituted molecules. Topological analysis of the electron density function for all molecules studied within the framework of Baders ‘atoms in molecules’ (AIM) theory revealed that introduction of a substituent into the ortho - or meta -position of the ring results in increasing of the contribution of the resonance forms different from the quinoid one. Contribution of the latter form is predominant for the structure of N , N -dimethyl-4-nitroaniline ( 1 ). Topological analysis of the electron density distribution was used to explain a decreasing of the molecular hyperpolarisabilites of the ortho - and meta -substituted compounds as compared with those for 1 .

X-ray crystal structures, molecular mechanics and quantum chemical calculations, and calculations of the nonlinear optical polarizabilities in the series of monohalogen substituted derivatives of dicyanovinylbenzene

Abstract The molecular and crystal structure of a series of potential non-linear optical (NLO) compounds — o-, m- and p-halogen-substituted derivatives of dicyanovinylbenzene, has been studied. The molecular geometry was investigated with an X-ray diffraction analysis and discussed along with results of the molecular mechanics (MM3) and ab initio quantum calculations (MP2 and DFT). The influence of the crystal packing on the molecular planarity has been revealed. Calculations of the dipole moments and molecular hyperpolarizabilities for molecules in question were carried out in the finite field approach. In addition to a several acentric compounds of this series found before, in the present investigation one more acentric crystal of the p-I substituted dicyanovinylbenzene was found (space group Pna21, Z=4). Second harmonic generation (SHG) of the laser light for this compound was confirmed by the Kurtz powder test.

A combinatorial chemistry approach to new materials for non-linear optics. I. Five Schiff bases

A combinatorial chemistry approach has been used to synthesize an array of Schiff bases, five of which, namely N-[(E, 2E)-3-(4-methoxyphenyl)-2-propenylidene]-3-nitroaniline, C(16)H(14)N(2)O(3), (1a), N-[(E, 2E)-3-(4-methoxyphenyl)-2-propenylidene]-4-nitroaniline, C(16)H(14)N(2)O(3), (2a), N-(E, 2E)-3-[4-(dimethylamino)phenyl]-2-propenylidene-3-nitroaniline, C(17)H(17)N(3)O(2), (1b), N-(E, 2E)-3-[4-(dimethylamino)phenyl]-2-propenylidene-4-nitroaniline, C(17)H(17)N(3)O(2), (2b), and N-(E, 2E)-3-[4-(dimethylamino)phenyl]-2-propenylidene-2-methyl-4-nitroanil ine, C(18)H(19)N(3)O(2), (3b), have been structurally characterized. A stack structure is observed for (1a) and (1b) in the crystal phase. Experimental and calculated molecular structures are discussed for these compounds which belong to a chemical class having potential applications as non-linear optical materials.

Indole- and carbazole-substituted pyridinium iodide salts: a rare case of conformational isomerism in crystals

A series of indole- and carbazole-substituted pyridinium iodide salts has been synthesized and characterized. X-ray analysis revealed that the iodide salt of the indole-substituted cation (E)-4-(1H-indol-3-ylvinyl)-N-methylpyridinium (IMPE(+)), C(16)H(15)N(2)(+) x I(-), (I), has two polymorphic modifications, (Ia) and (Ib), and a hemihydrate structure, C(16)H(15)N(2)(+) x I(-) x 0.5H(2)O, (II). Until now, only one crystal modification has been identified for the (E)-4-(9-ethyl-9H-carbazol-3-ylvinyl)-N-methylpyridinium (ECMPE(+)) iodide salt, C(22)H(21)N(2)(+) x I(-), (III). Crystals of (Ia) and (Ib) comprise stacks of antiparallel cations with iodide anions located in the channels between the stacks. Due to the presence of the water molecules, the packing in (II) is quite different to that found in (Ia) and (Ib), and positional disorder involving a statistical superposition of two rotamers of IMPE(+), with different orientations of the indole fragment, was found. Crystals of (III) contain two independent ECMPE(+) rotamers with different orientations of their carbazole substituents. The cations are packed in stacks, with the iodide anions located in the channels between the stacks. In (III), the iodide was found to be disordered over two sites, with occupancies of 0.83 and 0.17.