Methyl Benzylidene Aniline Research Articles

Intense THz Generation with New Organic NLO Crystal NMBA

AbstractLarge crystal growth and characterization of the optical and terahertz (THz) properties of organic nonlinear optical (NLO) crystal NMBA (4‐Nitro‐4′‐methylbenzylidene aniline) is presented. The reported method of crystal growth consistently produces high‐quality single crystals. The THz generation efficiency and optical properties of NMBA to other THz generation crystals including BNA and MNA are compared. The low THz absorptions that make NMBA an ideal source for THz time‐domain spectroscopy are highlighted.

Synthesis, Growth and Characterization of Organic Nonlinear Optical Single Crystals of 4-Bromo-4’-Methyl Benzylidene Aniline

Organic nonlinear optical material of 4-bromo-4’-methyl benzylidene aniline (BMBA) was synthesized and single crystal of BMBA was grown by solvent evaporation method at room temperature using ethanol as solvent. The crystalline nature of the grown crystals was confirmed using powder X-ray diffraction studies. The crystals were also characterized by single crystal X-ray diffraction method and their lattice parameters were determined. Thermal properties of BMBA were evaluated with thermogravimetric, differential thermal and differential scanning calorimetric analyses. Fourier transform infrared and FT-Raman spectral studies were carried out on the BMBA material to confirm the synthesized compound. 1H and 13C-nuclear magnetic resonance spectral studies were recorded to elucidate the structure of the grown crystals. Fluorescence spectrum recorded shows a peak at 485 nm. UV-Vis-NIR spectral analysis shows transmittance of ~92% in the visible region. The mechanical stability was analyzed by Vickers microhardness tester and the work hardening coefficient of the grown crystal was calculated. Second harmonic generation efficiency of the grown crystal measured by Kurtz powder technique is ~1.8 times that of potassium dihydrogen orthophosphate.

A first-principles study of linear and nonlinear optical properties of 4-nitro-4′-methylbenzylidene aniline

First-principles calculations of two second-order optical response functions as well as the dielectric function for 4-nitro-4(')-methylbenzylidene aniline are performed. Specifically, we evaluate the dielectric function and the second-harmonic generation (SHG) response coefficient over a wide frequency range. Electronic structure obtained from the full-potential projected augmented wave method is adopted in the calculation of optical properties. The calculated results of the refractive indices and the SHG are in good agreement with the experimental values. The linear and nonlinear optical spectra are analyzed and the origins of the peaks in the spectra are discussed in terms of the calculated electronic structure. It is found that the origin of the large nonlinear optical susceptibility is the charge transfer due to the strong "push-pull" effect. The study of the contributions of different transitions to the SHG coefficients shows that the virtual electron process is main. The contribution to the largest component chi(11) ((2)) of the virtual hole process is about 30% of the total static limit of the SHG coefficient. The prominent features in the spectrum of chi(11) ((2)) are successfully correlated with the features of the linear dielectric function epsilon(omega) in terms of single-photon and two-photon resonances.

Crystal structure and geometry-optimization study of 4-methyl-3′,5′-dinitro-4′-methyl benzylidene aniline

Schiff base 4-methyl-3′,5′-dinitro-4′-methyl benzylidene aniline was synthesized by the condensation of 4-amino-2,6-dinitrotoluene with 4-methylbenzaldehyde. The crystal of the title compound was obtained and it was characterized by X-ray single crystal diffraction analysis, EA, FTIR and 1H NMR. The geometry and normal vibrations have been obtained from the density functional theory (DFT) method with the B3LYP method employing the 6-31G** and 6-311G** basis sets. The calculated results propose that the latter is more accurate to the experimental data. The structural parameters from the theory are close to those of the crystal, and the computational frequencies are in agreement with the experimental data.

Growth and characterization of NMBA (4-nitro-4′-methyl benzylidene aniline) single crystals

The organic nonlinear optical crystal 4-nitro-4′-methyl benzylidene aniline (NMBA) having three-dimensional octahedral shape were grown from solutions with polar solvents by slow cooling method with one-dimensional needle-shaped seed crystals. X-ray powder diffraction study made on the grown crystals showed that they belong to monoclinic system with space group Pc. The grown crystals were characterized by different instrumental methods such as differential thermal analysis (DTA) and thermogravimetry (TG), infrared (IR) and nuclear magnetic resonance (NMR) spectral analyses and optical transmittance study. DTA and TG analysis ascertained purity of the synthesized, purified and grown NMBA material. IR spectral analysis reveals different functional groups present in the NMBA molecule. NMR spectral analysis examines different positions of hydrogen atoms in different chemical environments in the NMBA molecule. Optical transmission spectrum gives the optical transmission window of NMBA in the UV-Visible-Near IR region.

Growth of a novel nonlinear optical crystal 4-nitro-4′-methyl benzylidene aniline in different organic solvents

The organic nonlinear optical crystal 4-nitro-4′-methyl benzylidene aniline, also known as NMBA, was grown from solutions with different organic polar and non-polar solvents. NMBA single crystals with three different morphologies were obtained, viz. needles (one-dimensional), platelets (two-dimensional) and octahedral (three-dimensional). Large size three-dimensional octahedral crystals were grown with one-dimensional needles as seeds. All the grown crystals were subjected to X-ray powder diffraction analysis and the results reveal that all of them belong to monoclinic system with space group Pc. Lattice parameters calculated from the X-ray data are in line with the literature value.

Influence of hydrogen bonding on the second harmonic generation effect: neutron diffraction study of 4-nitro-4'-methylbenzylidene aniline.

A neutron diffraction study of the non-linear optical (NLO) material 4-nitro-4'-methylbenzylidene aniline (NMBA) is presented. NMBA exhibits a large macroscopic second-order NLO susceptibility, chi((2)), and this study shows that hydrogen bonding is, in part, responsible for this. No hydrogen bonding was reported in the X-ray study [Ponomarev et al. (1977). Sov. Phys. Crystallogr. 22, 223-225], whereas the present work shows that C-H.X hydrogen bonds (where X = N, O or pi) direct the nature of the three-dimensional lattice. C-H.X (X = N or O) hydrogen bonds are common; however, C-H.pi hydrogen-bond motifs are relatively rare. Such intermolecular interactions help extend the molecular charge transfer into the supramolecular realm, the charge transfer originating as a consequence of the high level of molecular planarity and strong donor-to-acceptor interactions. Molecular planarity, coupled with the favourable nature of the hydrogen bonds, results in parallel stacking of molecules in both the a and c crystallographic directions with extremely close interplanar spacings. Such a combination of influential hydrogen-bonding characteristics accounts, in part, for the large second-order NLO output of the material since the phenomenon is so critically dependent upon the nature of the charge transfer.

Influence of organic solvents on the habit of NMBA (4-nitro-4′-methyl benzylidene aniline) crystals

The habits of NMBA crystals grown with 10 different organic solvents having different dipole moments were studied. Solubility of NMBA in all the above solvents at various temperatures in the range 293–318 K was determined by Gravimetric method and the corresponding solubility coefficients at different growth temperatures were calculated. Crystals were grown by restricted evaporation method. Crystals with three different habits were obtained viz; needles (one-dimensional), platelets (two-dimensional) and octahedral (three-dimensional). All the grown crystals were found to be monoclinic which was confirmed by X-ray powder diffraction analysis and the lattice parameters calculated from this study are in line with the literature value.

Thermal properties of the organic nonlinear optical crystal 4-nitro-4′-methylbenzylidene aniline

The thermal properties of high-quality nonlinear optical single crystals of 4-nitro- 4′-methylbenzylidene aniline (NMBA) have been measured in various temperature ranges. The specific heat was measured in the range from 273 to 373 K by differential scanning calorimetry and was found to obey the relationship Cp=2.3×10−3 T+0.487 J g−1 K−1. The peak melting point was detected at a temperature of 402 K with a corresponding enthalpy of melting ΔHm of 113.63 J g−1. Principal thermal expansion and thermal conductivity coefficients were determined at different temperatures. For example, at room temperature (295 K) they were α1=1.274×10−4 K−1, α2=0.826×10−4 K−1, and α3=0.239×10−4 K−1. The principal thermal conductivity coefficients were k1=0.40 W m−1 K−1, k2=0.19 W m−1 K−1, and k3=0.21 W m−1 K−1 and these values were independent of temperature up to 370 K.

The linear and nonlinear optical properties of the organic nonlinear material 4-nitro-4′-methylbenzylidene aniline

The organic crystal 4-nitro-4′-methylbenzylidene aniline (NMBA) was identified as a promising nonlinear material by the powder technique. The material gave a second harmonic intensity 16 times that of urea. Large single crystals of dimensions 5×3×1 cm3 were grown by the temperature lowering of a seeded supersaturated ethyl acetate solution. The principal dielectric axes were defined by orthoscopic examination. The dispersions of the refractive indices were determined to an accuracy of ±0.0015 using the minimum deviation technique and Maker fringe spacings. These dispersion curves were fitted to a Sellmeier equation which allowed the indices to be determined to ±0.0006. The nonlinear d coefficients d11, d33, d31, and d13 were evaluated at 1000, 1064, and 1300 nm using the Maker fringe technique. The coefficient d11 was over 200 times larger than potassium dihydrogen phosphate (KDP) d36. In addition, the nondiagonal coefficient d31 was similar to the phase-matching coefficient in the organic material 3-acetamido-4-dimethylamino-nitrobenzene (DAN). Critically phase-matched second harmonic signals were observed at all fundamental wavelengths. There was excellent agreement between the experimentally determined and theoretical phase-matched incidence angles. Noncritical phase-matched conditions have been calculated and are reported. Both angle and wavelength noncritical phase matching is possible with this crystal.

Linear electro-optic effect and temperature coefficient of birefringence in 4-nitro–4′-methylbenzylidene aniline single crystals

A study of the linear electro-optic effect in single crystals of the organic compound, 4-nitro–4′-methylbenzylidene aniline is reported. The reduced half-wave voltages have been found to have values 2.8, 1.3, and 1.1 kV at 632.8, 514.5, and 488.0 nm, respectively and the corresponding values of the largest linear electro-optic coefficient have been calculated. The thermal variation of the birefringence has also been investigated and the temperature variation of the refractive index difference is found to have the value, dΔn/dT = 15.8 × 10−5 K−1.

The growth, perfection and properties of organic non-linear optical materials I. 4-nitro-4′-methyl benzylidene aniline

Single crystal specimens of the organic non-linear optical material 4-nitro-4′-methyl benzylidene aniline (NMBA) have been grown from the melt (Bridgman technique) and from solution (slow cooling technique). Crystals produced by the former technique were strained, principally due to the instability of the material in the melt and the tendency of the decomposition products to accumulate in the solid during growth. Crystals grown from solution were of much higher perfection exhibiting the forms: (010), {111}, {011} (all dominant) and (10 2 ), (100) (less dominant) predicted by theoretical calculations of the equilibrium form. The rhombic shaped crystals which occasionally contained striations parallel to the (10 2 ) plane were grown to sizes of 5x3x0.5 cm 3 (maximum dimensions). Large volumes of the crystals were optically clear and unstrained. From these could be prepared cut and polished specimens (0.5×0.3×0.2 cm 3) for structural and optical assessment.

The linear electro-optic response in crystals of 4-nitro-4′-methyl benzylidene aniline (NMBA)

Thin film crystals of 4-nitro-4'-methyl benzylidene aniline (NMBA) grown in an acentric crystal form exhibit a moderate low frequency electro-optic (e-o) response. The dispersion in the e-o figure of merit n 3 r has been measured using polarisation interferometry in a through-film geometry. For wavelengths in the range 600 nm to 1550 the dispersion of the e-o figure of merit is close to what may be expected off-resonance. The magnitude of n 3 r in NMBA is consistent with previous measurements of second harmonic generation indicating that the response is largely electronic in origin.

Second Order Optical Non-Linearity and Phase Matching in 4-Nitro-4′- Methyl benzylidene Aniline (NMBA)

Abstract Large single crystals (5 × 4 × 1 cm3) of the noncentrosymmetric, monoclinic form of the organic crystal (NMBA) have been prepared by seeded growth from supersaturated solutions. Optically clear volumes permitted the preparation of polished specimens with faces parallel to the (100) and (010) directions. These were examined by the Maker fringe technique. The sections showed no dispersion of the dielectric axes with wavelength in the range 440–630 nm. The χ2 elements d11 and d23 were found to be 4 and 143 respectively relative to quartz d11. Type II phase matching was observed using 1064 nm light at and near to normal incidence to the (100) plane with an efficiency of ≈10% of that for a 2-(N,N-dimethylamino)-5-nitroacetanilide (DAN) crystal of the same thickness tested under identical conditions. Since the half angle between the molecular dipoles in the monoclinic NMBA crystal is 12°; a far from optimal angle for efficient phase matching, this lower efficiency was expected.