Benzylidene Aniline Research Articles

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.

Preparation and Chemistry of an Unexpectedly Stable α-Oxoketene−Pyridine Zwitterion, 2,2-Bis(tert-butylcarbonyl)-1-[4-(dimethylamino)pyridinio]ethen-1-olate

Treatment of dipivaloylketene 1 and its dimers 2 and 3 with 4-(dimethylamino)pyridine (DMAP) in acetonitrile affords the alpha -oxoketene-pyridine zwitterion 4 as a pale yellow solid. This is the first example of a stable zwitterion obtained from a true alpha -oxoketene. In anhydrous solution at room temp., compound 4 largely cleaves into the reactants 1 and DMAP. At -60 degreesC the equilibrium is shifted entirely towards the zwitterion 4, as shown by C-13 NMR measurements. Calculations using density functional theory (B3LYP/6-311+G**) are in excellent agreement with the formation and relative stability of 4. N-15 labelling experiments demonstrate that the ring nitrogen atom of DMAP is involved in generating the new zwitterionic C-N bond. Reactions of 4 with NH and OH nucleophiles in solution afforded the corresponding dipivaloyl acetic acid derivatives 6 and 7, whereas acetone or benzylidene aniline undergo cycloaddition reactions of the hetero-Diels-Alder type.

Crystal and molecular structure of N-(p-nitrobenzylidene)-3-chloro-4-fluoroaniline

The crystal structure of N-(p-nitrobenzylidene)-3-chloro-4-fluoroaniline (II) has been determined by X-ray structure analysis. This belongs to a class of benzylidene anilines. The structure was solved by direct method. The molecular packing of the non-planar molecules are held by Van der Waals and F…H7, O…Cl, F…F and N…H interactions.

Vibrational Spectra of Benzylidene Aniline, O-Hydroxybenzylidene O-Hydroxyaniline and its Complexes with Cu(II) and NI(II) Metal Ions

The FTIR and FT Raman spectra of benzylidene aniline, and o-hydroxybenzylidene o-hydroxyaniline compounds in the solid state in the wavenumber (1800-200 cm−1) are recorded. An assignment for nearly all fundamentals are proposed. Comparison of the spectra of trans stilbene and benzylidene aniline reveals that v N-Ph stretch for the latter compound is situated at 1368 cm−1 in the IR spectra with medium intensity. for o-hydroxybenzylidene o-hydroxyaniline, the stretching modes v N-Ph, and v C-Ph are observed at 1356 and 1226 cm−1 respectively. the two v O-Ph are observed as intense bands in the IR spectra at 1245 and 1278 cm−1, respectively. the FTIR spectra of the o-hydroxybenzylidene o-hydroxyaniline complexes with Cu(II) and Ni(II) metal ions are also recorded and assigned.

Crystallization kinetics study on N-(p-n-alkyloxybenzylidene)-p-n-alkylanilines (nO.m compounds)

A comparative systematic kinetic study of crystallization among various smectogens of higher homologues of the benzylidene aniline nO.m series (9O.2, 13O.2, 14O.2, 15O.2, 16O.2, 2O.16, 11O.16, 16O.16 and 18O.16) has been carried out by thermal microscopy and differential scanning calorimetry (DSC). The DSC thermograms were run from crystallization temperature to the isotropic melt for different time interval. The liquid crystalline behaviour together with rate of crystallization of smectic ordering in newly synthesized nO.m compounds (16O.2, 2O.16, 11O.16, 16O.16, 18O.16) with respect to their lower homologues are discussed in relation to the kinetophase (which occurs prior to the crystallization), end chain lengths, the odd-even effect and chain length ratio. The molecular mechanism and dimensionality in the crystal growth were computed from the Avrami equation. The characteristic crystallization time (t*) at each crystallization temperature was deduced from the individual plots of log t vs. DeltaH. Further, a qualitative approach was made to the crystallization process in smectic layers.

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.

Synthesis and Structural Characterization of Azatitanacyclobutane Derivatives

The titanocene vinylidene intermediate [Cp*2Ti=C=CH2] (9) reacted with the carbodiimides R−N=C=N−R [R = p-CH3C6H4 (19a), C6H11 (19b)] to give the N=C-cycloaddition products [Cp*2Ti{−NR−C(=NR)−(C=CH2)−}] [(R = p-CH3C6H4 (20a), C6H11 (20b)]. The X-ray structure of 20a in form of a surprisingly stable n-hexane clathrate is presented. The azatitanacyclobutane [Cp*2Ti{−NPh−C(Ph)(H)−(C=CH2)−}] (22) was formed from the reaction between 9 and benzylidene aniline [PhN=C(Ph)H (21)]. Reactivity studies showed that azatitanacyclobutanes are unreactive upon typical ring-enlargement reactions as observed for other four-membered titanacycles.

Synthesis of Azetidines from Imines with 2,3-Dihydrofuran under High Pressure.

6, 7-Aryl-2-oxa-7-azabicyclo[3. 2. 0]heptane compounds were obtained from arylimines with 2, 3-dihydrofuran under high pressure. When benzylidene aniline used as imine, 6, 7-diphenyl-2-oxa-7-azabicyclo[3. 2. 0]heptane was obtained 66% yield with 87% selectivity. This reaction was promoted by pressure and the yield and the selectivity of the reaction were increased by temperature. The mechanism of the reaction was considered zwittenonic route was favored.

Theoretical calculations of the structure of a donor—acceptor stilbene, azobenzene and related molecules

The structures of a substituted stilbene, azobenzene, and two isomeric benzylidene anilines containing the 4-dimethyl-amino group at one end of the molecule and the 4′-nitro group at the other, have been calculated using the semiempirical MNDO, AM1, and PM3 methods and the ab initio HF/3-21G method. The results are compared with experimental data where available. The MNDO method gives a very poor account of the geometry of the stilbene, but both the AM1 and PM3 methods correctly predict the planarity of the substituted stilbene and nitrobenzylidene aniline but erroneously predict a non-planar structure for the azobenzene. In contrast, the ab initio method predicts planar structures for the substituted stilbene, azobenzene, and nitrobenzylidene aniline, and a twisted structure for the isomeric benzylidene nitroaniline, in line with crystallographic data. This loss of planarity for the benzylidene nitroaniline is almost certainly responsible for its smaller non-linear activity and for the hypsochromic shift observed in its low energy absorption band relative to the other molecules.

Liquid crystals of 4-octyloxy-N-(benzylidene)aniline derivatives bearing trifluoromethyl or trifluoromethoxy end groups

Abstract Seven new derivatives of 4-octyloxy-N-(4-substituted benzylidene) aniline have been synthesized. 4-Trifluoromethyl and 4-trifluoromethoxy derivatives exhibit stable smectic B and A phases, respectively, while both the 4-methyl and 4-methoxy derivatives have monotropic nematic phases. Fundamental liquid crystalline properties such as entropies of the phase transitions, microscopic textures, smectic layer spacings, orientational order parameters, and molecular dipole moments were determined. It has been revealed that moderately polar nature of these mesogens act to stabilizing monolayer smectic states. The smectic A phase of 4-trifluoromethoxy derivative exhibit very high orientational order. None of the disubstituted compounds, 3,5-bis(trifluoromethyl), 3,5-dimethyl, and 3,5-dimethoxy derivatives were mesogenic. The effect of terminal trifluoromethylation on the liquid crystalline properties is discussed.

UV-Visible Spectrophotometric Investigations of Charge Transfer Complexes of Some P-N,N-Dimethylaminobenzylidene Ailines with the New Acceptor PFB and CA Acceptor

Abstract The CT complexes of PFB and CA acceptors with eleven benzylidene anilines donors have been investigated spectro-photometrically in the uv-visible region for the first time. The values of Ip of these compounds have been estimated from their complexes with CA, the values are in the range of 8.64–8.96 ev. From these values the constants of the new acceptor PFB a, b, c1, c2 and Ea have been calculated, the values are 0.91, -5.31, 7.13, 1.97, and 1.37 ev, respectively. The CT parameters of our donors with PFB and CA acceptors, ζCT, KCT ΔG° and W have also been estimated and discussed.

Molecular orbitals and optical nonlinearities for symmetrically substituted benzylidene anilines

Molecular structure and orbitals are calculated for symmetrically substituted benzylidene anilines. From calculation of the electronic structure, the third harmonic generation is approximately explained by a three-level system in which the A g excited state plays an important role. The molecular orbitals that contribute to χ (3) are clarified. From the calculation relating to the displacement of atoms, it is found that symmetry is broken at the optimum point of the B u excited state. This phenomenon contributes to χ (3) in situations such as the two-photon resonance region.

Theory of molecular optoelectronics. X: Calculations for MBANP and NMBA

AbstractComponents of the crystal quadratic susceptibility tensor x(2) for second‐harmonic generation are calculated for the title compounds 2‐(α‐methyl benzylamino)‐5‐nitropyridine (MBANP) and 4‐nitro‐4'‐methyl(benzylidene aniline) (NMBA). Input data are the crystal structure and refractive indices and CNDO hyperpolarizabilities. The calculations also yield effective polarisabilities and local electric fields. Susceptibility components reach 66 pm V−1 in MBANP and 27 pm V−1 in NMBA in the crystal axes; agreement with experiment is poor for MBANP but satisfactory for NMBA. These features seem to reflect the better defined charge transfer axis in NMBA. Screened dipole–dipole interactions calculated from CNDO dipole moments stabilise MBANP by 70 kJ mol−1 and NMBA by 20 kJ mol−1 and imply permanent electric fields of a few GV m−1.

Molecular Orbitals and Third-Harmonic Generation for Symmetrically Substituted Benzylidene Aniline

Molecular orbitals and third-order susceptibility are calculated for terephthal-bis-(4-N,N-diethylamino aniline). The main mechanism of third-harmonic generation is explained approximately by a three-level system. The effect of the orbital shape upon the susceptibility is analyzed. It is found that molecular orbital distortion, due to introduced nitrogen atoms, enhances the transition moment between excited states, 1Bu-2Ag, and this contributes to the third-order susceptibility.

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.

DSC characterisation of various phase transitions in mesomorphic benzylidene anilines

AbstractTo analyse the order of the phase transitions in a number of mesomorphic benzylidene anilines, the DSC (Differential Scanning Calorimetry) method proposed by NAVARD and HAUDIN is used. This method involves the measurement of the ratio (N) of the DSC peak heights H2/H1 for a given transition, performed with two different heating rates (T2/T1). N is a function of the ratio r2/r1(= R) and the magnitude of N provides a simple way to characterize the order of a phase transition.

Synthesis and characterization of new polyimides and polyamide-imides containing azomethine group in the polymer backbone

New aromatic polyimides and polyamide-imides containing azomethine linkages in the polymer backbone have been synthesized by reacting 4,4′-bis(isocyanato) benzylidene aniline (AZMI) with pyromellitic dianhydride (PMDA), 3,3′, 4,4′-benzophenone tetracarboxylic dianhydride (BTDA) and trimellitic anhydride (TMA) by one-step method. The AZMI was synthesized from 4,4′-bis(carboxy) benzylidene aniline (AZMA) by a Weinstock modified curtius rearrangement. All the polycondensation reactions were carried out in N-methyl-2-pyrrolidone (NMP) and the polymers obtained were characterized by infrared spectroscopy, solution viscosity, elemental analysis, thermogravimetric analysis, differential scanning calorimetry and X-ray diffraction.

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.

Conformation of p‐dimethylamino aza styryl dyes

AbstractConformational studies on some p‐dimethylamino β‐aza and β‐aza (with respect to the dimethylamino phenyl ring) styryl dyes derived from quinoline‐4, quinoline‐2, pyridine‐4, pyridine‐2, and benzothiazole‐2 have been carried out using the quantum mechanical PCILO (perturbative configuration interaction using localized orbitals) method. These molecules may be considered as heterocyclic analogues of benzylidene anilines whose conformations have been studied extensively by both theoretical and experimental methods to explain the difference of their spectra from the isoelectronic benzylidene compounds. The results of the present studies show that the β‐aza styryl dyes are nearly planar. In case of β‐aza styryl dyes, although the phenyl ring is coplanar with the central atoms, there is a substantial twist of the heterocyclic ring. These results are explained in terms of CT‐1 and CT‐2 effects and are used as a possible explanation for the observed spectral and sensitization properties.