M. Delower H. Bhuiyan

Geometry and bond-length alternation in nonlinear optical materials. I. Standard parameters in two precursors

2-{3-Cyano-4-[4-(N-formylanilino)-trans-1,3-butadienyl]-5,5-dimethyl-2,5-dihydrofuran-2-ylidene}propanedinitrile, C(22)H(18)N(4)O(2), (I), and 2-{3-cyano-4-[6-(N-formylanilino)-trans,trans-1,3,5-hexatrienyl]-5,5-dimethyl-2,5-dihydrofuran-2-ylidene}propanedinitrile, C(24)H(20)N(4)O(2), (II), show the alternating single/double-bond behaviour of push-pull chromophores. In the two structures, the planar polyene chains are twisted with respect to the furanylidene ring by 18.2 (2) and 12.4 (2) degrees , respectively. Comparison with structures of related and parent molecules shows subtle but consistent bond-length variations consistent with charge-delocalized structures. Crystal cohesion is provided by various sets of hydrogen bonds, viz. C-H(methyl)...N(cyano) and bifurcated (C=C-H)(2)...O=C in (I), and C-H(methyl/phenyl)...O and C=C-H...N(cyano) in (II).

Second-order nonlinear optical properties of zwitterionic chromophores

The molecular linear and second-order nonlinear optical (NLO) properties of a series of donor (D)-π-acceptor (A) merocyanine molecules have been studied in three solvents, dimethylformamide (DMF), tetrahydrofuran (THF), and chloroform (CHCl3). All the compounds have a cyanodicyanomethylidenedihydrofuran electron acceptor system with either a pyridinylidene or quinolinylidene donor group. In high polarity solvents the molecules with a quinolinylidene donor have larger first hyperpolarizabilities than those with a pyridinylidene donor, while the opposite is true in low polarity solvents. The molecules under investigation have an aromatizable donor unit, which leads to a high degree of charge separation in the ground-state; as a result they have a strong tendency to aggregate. To minimize these interactions arene-rich bulky groups have been introduced in a number of these compounds.

Geometry and bond-length alternation in nonlinear optical materials. II. Effects of donor strength in two push–pull molecules

The compounds N-[2-(4-cyano-5-dicyanomethylene-2,2-dimethyl-2,5-dihydrofuran-3-yl)vinyl]-N-phenylacetamide, C(20)H(16)N(4)O(2), (I), and 2-{3-cyano-5,5-dimethyl-4-[2-(piperidin-1-yl)vinyl]-2,5-dihydrofuran-2-ylidene}malononitrile 0.376-hydrate, C(17)H(18)N(4)O x 0.376 H(2)O, (II), are novel push-pull molecules. The significant bonding changes in the polyene chain compared with the parent molecule 2-dicyanomethylene-4,5,5-trimethyl-2,5-dihyrofuran-3-carbonitrile are consistent with the relative electron-donating properties of the acetanilido and piperidine groups. The packing of (I) utilizes one phenyl-cyano C-H...N and two phenyl-carbonyl C-H...O hydrogen bonds. Compound (II) crystallizes with a partial water molecule (0.376H(2)O), consistent with cell packing that is dominated by attractive C-H...N(cyano) interactions. These compounds are precursors to novel nonlinear optical chromophores, studied to assess the impact of donor strength and the extent of conjugation on bond-length alternation, crystal packing and aggregation.

High Electro-Optic Coefficient in Organic NLO Polymers: Poling and Study of the Relaxation Process

We report a high electo-optic coefficient (r33) of 175 pm/V in guest-host polymer films made by mixing amorphous polycarbonate with the chromophore, PYR-3 that was synthesized by our team. We have previously shown that PYR-3 has a large 2nd order nonlinear optical figure of merit. The measured r33 is five times larger than that of conventional inorganic materials such as lithium niobate. The decay of r33 with time has been studied for more than 1000 hours at room temperature and ambient atmosphere, and we find that the r33 value gradually reduced to a stable value of 34 pm/V after 40 days.

C-H⋯π packing inter-actions in 2-[5,5-bis-(4-benzyl-oxyphen-yl)-3-cyano-4-methyl-2,5-dihydro-furan-2-yl-idene]malononitrile.

The title molecule, C35H25N3O3, packs utilizing C—H⋯π attractive interactions causing the identical 4-benzyloxyphenyl groups to pack with different conformational angles. This difference is consistent with the variable interplanar dihedral angles found in closely related structures.

5-(4-Cyano-5-dicyano­methyl­ene-2,2-dimethyl-2,5-dihydro-3-fur­yl)-3-(1-methyl-1,4-dihydro­pyridin-4-yl­idene)pent-4-enyl 3,5-bis­(benz­yloxy)benzoate acetonitrile 0.25-solvate: a synchrotron radiation study

The title compound, C42H36N4O5·0.25CH3CN, crystallizes with a partial twofold disordered (1/4) acetonitrile solvent of crystallization. The linking atoms to the 3,5-bis(benzyloxy)benzoic acid are disordered between two conformations in the ratio 0.780 (6):0.220 (6). In the crystal, the molecules pack using mainly C—H⋯N(cyano) interactions coupled with weak C—H⋯O(ether) interactions and C—H⋯π interactions. A brief comparison is made between a conventional and this synchrotron data collection.

2-{3-Cyano-5,5-dimethyl-4-[4-(pyrrol-idin-1-yl)buta-1,3-dien-yl]-2,5-dihydro-furan-2-yl-idene}malononitrile dichloro-methane solvate.

The structure of the title compound, C18H18N4O·CH2Cl2, was solved using data collected from a multiple crystal (note high R factors). The crystal structure is dominated by two bifurcated attractive C—H⋯N(cyano) interactions.

2-(3-Cyano-4-{7-[1-(2-hy-droxy-eth-yl)-3,3-dimethyl-indolin-2-yl-idene]hepta-1,3,5-trien-yl}-5,5-dimethyl-2,5-dihydro-furan-2-yl-idene)malononitrile.

The title compound, C29H28N4O2, excluding the hydroxyethyl and methyl groups, is slightly twisted from planarity so that the terminating indol-2-ylidene and furan-2-ylidene moiety planes subtend a dihedral angle of 6.27 (8)°. A small inwards fold in the polymethine atom chain is consistent with centrosymmetric dimer formation via O—H⋯N(cyano) hydrogen bonds. In the crystal, the molecules pack in layers approximately parallel to the (10) plane via pairs of O—H⋯N and C—H⋯N(cyano) interactions.

Bis[4-(dimethyl­amino)phen­yl]diazene oxide

The asymmetric unit of the title compound, C16H20N4O, contains six independent approximately planar molecules and is best described as a commensurate modulation of a P21/c parent. Two sets of disordered molecules share almost the same locations (related by an in-plane translation), ensuring that the c-glide plane condition is not attained. C—H⋯O interactions provide structural cohesion. The site occupancy factors of the disordered molecules are ca 0.72/0.28 and 0.67/0.33.

Synthesis of a Tri Chromophore System for Electro-Optic Applications

The synthesis of a suite of compounds containing three chromophores coupled to a central nitrogen atom are reported. X-ray crystallographic data has been obtained for two of the compounds and this suggests that incorporation of these molecules into such a trichomophore bundle is a valid strategy for minimizing dipole-dipole interactions, and therefore aggregation in these compounds.