Ronald D. Clark

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 .

Systematic study of polymorphism in crystalline non-linear optical materials

Abstract Crystalline polymorphism is quite common for non-linear optical (NLO) compounds. During our studies of NLO materials we found several compounds that crystallize in two or more forms. We present a short review of our recent data on the crystalline polymorphism of NLO compounds. Among the compounds studied, we found examples of concomitant polymorphism, induced conformational polymorphism, and organic polytypism. For several compounds, X-ray data are discussed along with computational data on molecular and crystal structure energy.

Optical limiting behavior of octa-decyloxy metallo-phthalocyanines

One of the key issues involved in the development of passive optical power limiters is the search for appropriate materials that show effective reverse saturable absorption. Metallo-phthalocyanines seem to be good candidates for such applications because of their high optical nonlinearity and their unique electronic absorption characteristics. A series of 1,4,8,11,15,18,22,25-octa-decyloxy metallo-phthalocyanines containing palladium, nickel, cobalt, copper, and zinc as central metal atoms were characterized for their nonlinear absorptive properties to evaluate their suitability to function as reverse saturable absorbers. Nonlinear transmission measurements were analyzed in terms of a five-state model and a simple model based on the effective excited-state absorption cross sections without ascribing their origin to the states involved. Optical limiting thresholds were also estimated and compared with the absorption cross sections.

One-pot polymorphism of nonlinear optical materials. First example of organic polytypes

Two nonlinear optical materials 1,1-dicyano-4-(4-dimethylaminophenyl)-1,3-butadiene (I) and 3-methoxydicyanovinylbenzene (II) have been investigated with regard to crystal growth, polymorphism, structure characterization and physical properties. It was found that both compounds form one-pot (concomitant) polymorphs, that might also be described as organic polytypes. Both polymorphs of compounds I and II form identical molecular layers with molecules located in the layer plane. In the two phases of compound I the layers superposition and their sequence differs significantly. This circumstance most probably determines the different color of the two crystal modifications. In the two crystal phases of compound II molecular layers and their superposition types are almost identical. The only difference between the phases is the sequence of the layer superposition. Single crystal and powder X-ray diffraction techniques, powder test for second harmonic generation, UV spectroscopy, and computational methods were used for characterization of these compounds.

Molecular modeling and experimental study of non-linear optical compounds: monosubstituted derivatives of dicyanovinylbenzene

Abstract A search for potential non-linear optical (NLO) compounds has been performed using the Cambridge Structural Database and molecular modeling. We have studied a series of monosubstituted derivatives of dicyanovinylbenzene as the NLO properties of one of its derivatives (o-methoxy-dicyanovinylbenzene, DIVA) were described earlier. The molecular geometry in the series of the compounds studied was investigated with an X-ray analysis and discussed along with results of molecular mechanics and ab initio quantum chemical calculations. The influence of crystal packing on the molecular planarity has been revealed. Two new compounds from the series studied were found to be active in the second harmonic generation (SHG) in the powder state. The measurements of the SHG efficiency have shown that the o-F-, and p-Cl-derivatives of dicyanovinylbenzene are about 10 and 20 times more active than urea, respectively. The peculiarities of crystal structure formation in the framework of balance between the van der Waals and electrostatic interactions have been discussed. The crystal morphology of DIVA and two new SHG-active compounds have been calculated on the basis of the known crystal structures.

Molecular Design and Non-Linear Optical Properties in the Series of Substituted Dicyanovinylaromatics

Abstract X-Ray single crystal study, molecular mechanics calculations and quantumchemical calculations of the static nonlinear optical (NLO) polarizabilities (β) were performed for a large series of dicyanovinylaromatic derivatives in order to make conclusions about the relationship between their molecular geometry, crystal structure and NLO properties. For some compounds studied EFISH measurements of the P values in solutions were made and good correlation was found between the calculated and experimental values. X-Ray data and optimal molecular associate calculations revealed the factors responsible for formation of centric/acentric crystal structures. This approach might be useful for prediction of possible crystal structures for simple organic chromophores. In the series studied only three acentric crystal structures were found, and in agreement with their molecular, electronic and crystal packing characteristics all were found to be active in second harmonic generation (SHG) in the solid state. For t...

Structure and nonlinear optical properties of phenylazo compounds. Structural characterization of 3-amino-3-morpholinyl-2-(o-nitrophenylazo)-propenonitrile and o-nitrophenylhydrazonomalononitrile

Abstract The results of synthesis, X-ray and spectral investigations, powder second harmonic generation (SHG), molecular mechanics and quantum chemical calculations of the potential nonlinear optical compound, 3-amino-3-morpholinyl-2-( o -nitrophenylazo)-propenonitrile (I) and its synthetic precursor o -nitrophenylhydrazonomalononitrile (II) are presented. The interrelations of molecular structure and crystal packing characteristics, important for SHG prediction, are discussed on the basis of molecular mechanics dimer structure calculations and the results of X-ray investigations. The conclusions about the low probability of SHG by compound I in the crystal form, in spite of its high calculated molecular hyperpolarizability value, are confirmed by powder SHG measurements.

A combinatorial chemistry approach to new materials for non-linear optics. II. 4-(Dimethylamino)cinnamaldehyde and a molecular complex of 4-methoxycinnamaldehyde with 2,4-dinitroaniline

The combinatorial chemistry approach has been used to synthesize an array of Schiff bases. The structures of five of these Schiff bases have been confirmed by X-ray analysis [Nesterov, Timofeeva, Borbulevych, Antipin & Clark (2000). Acta Cryst. C56, 971-975]. In two cases, the reaction conditions were not sufficient to obtain the products in question. In one case, a molecular complex, C(10)H(10)O(2).C(6)H(5)N(3)O(4), of the starting products 4-methoxycinnamaldehyde and 2,4-dinitroaniline was found. X-ray analysis revealed hydrogen-bond formation between the molecules of these reagents in the crystal. In the other case, X-ray analysis demonstrated that no chemical reaction occurred under the reaction conditions, and only one starting reagent, 4-(dimethylamino)cinnamaldehyde, C(11)H(13)NO, was found in the precipitate.

Growth and characterization of crystalline films of meta-nitroaniline (mNA) and 2-cyclo-octylamino-5-nitropyrydine (COANP)

The crystallization features of thin single crystalline films of mNA and COANP compounds grown between two fused quartz plates, one of which has a recess in the middle, are described. The depth of the recessed spot was of the grown crystal thickness which range d form 1 to 10 micrometers. A possible explanation of the crystallization peculiarities of the COANP compound is given .The crystallographic and optical indicatrix orientations of the crystal s are discussed, and applied to measurement of the efficiency of the second harmonic of the Nd:YAG laser operating at 1.064 micrometers, and generated by our films. The pattern of the intensities of the second harmonic generation is discussed, and a possible explanation of the discrepancy between the experimental and theoretical data is given.

Modified Bridgman-Stockbarger growth of a novel NLO organic crystal (2-methoxyphenyl)-methylene-propanedinitrile

Abstract The Bridgman-Stockbarger method offers a unique opportunity for positioning the solid-liquid interface in the hot zone by a suitable adjustment of the two zone temperatures. The method, however, yields inhomogeneous organic crystals in relation to the progressive degradation of the material during growth. To solve this problem, a modified Bridgman-Stockbarger method (MBS) has been developed and is used to keep the smallest possible quantity of product in the melt for a short time period. In this method, the gradient is chosen to be 5 to 10°C/cm and the ampoules downward rate is chosen to be 0.1 to 0.3 mm/h. For the given conditions, several (2-methoxyphenyl)-methylene-propanedinitrile or 2-dicyanovinylanisole (DIVA) single crystals of good optical quality and a size of 10 × 10 × 50 mm 3 have been successfully grown. Preliminary results on the characterization of these crystals are presented.