Structural, proton-transfer, thermodynamic and nonlinear optical studies of (E)-2-((2-hydroxyphenyl)iminiomethyl)phenolate

Spectroscopic and mechanistic insights into solvent mediated excited-state proton transfer and aggregation-induced emission: introduction of methyl group onto 2-(o-hydroxyphenyl)benzoxazole

2-(2-Hydroxy-5-methylphenyl)benzoxazole(HBO-pCH3), a solvatochromic benzoxazole-based probe, exhibited a typical dual fluorescence phenomenon, high fluorescence quantum yield, red-shifted emission and large Stokes’ shift via the ESIPT in solvents.

Transient absorption, femtosecond dynamics, vibrational coherence and molecular modelling of the photoisomerization of N-salicylidene-o-aminophenol in solution

This article presents a study of the excited state relaxation dynamics of N-salicylidene-o-aminophenol (SOAP) in ethanol solution. Femtosecond transient absorption (TA) spectroscopy and theoretical calculations are used in combination to establish the mechanism of the excited state relaxation and type of molecular species involved in the accompanying phototransformations. TA spectra show that upon photoexcitation two SOAP tautomers (E-enol and Z-keto) interconvert by ESIPT. The molecule can subsequently isomerize to the E-keto form of SOAP. An intriguing observation is that the TA spectra of this compound in ethanol show modulations of the signal at the stimulated emission spectral range. It is found that these modulations are due to the coherence of the excited ensemble of molecules whose evolution over time represents a moving wave packet. After Fourier transform of the modulations, two characteristic frequencies are identified. These frequencies refer to the corresponding vibrational modes of the excited state and their nature is elucidated by DFT quantum chemical calculations. The obtained experimental and theoretical data reveal the nature of the vibronic coupling between the ground and excited state and the type of molecular vibrations involved in the molecular dynamics along the potential surface of the first excited state at the initial moment right after excitation. These vibrations characterize the starting point in the excited state dynamics of the molecule toward Z-E isomerization of the keto form of SOAP. This study provides a comprehensive picture of the dynamic processes taking place upon photoexcitation of the compound, which might enable control over the various relaxation channels.

Crystal structure, Hirshfeld surface analysis and DFT studies of (E)-4-methyl-2-{[(4-methyl-phen-yl)imino]-meth-yl}phenol

In the title compound, C15H15NO, the configuration of the C=N bond of the Schiff base is E, and an intra-molecular O-H⋯N hydrogen bond is observed, forming an intra-molecular S(6) ring motif. The phenol ring is inclined by 45.73 (2)° from the plane of the aniline ring. In the crystal, mol-ecules are linked along the b axis by O-H⋯N and C-H⋯O hydrogen bonds, forming polymeric chains. The Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the packing arrangement are from H⋯H (56.9%) and H⋯C/C⋯H (31.2%) inter-actions. The density functional theory (DFT) optimized structure at the B3LYP/ 6-311 G(d,p) level is compared with the experimentally determined mol-ecular structure, and the HOMO-LUMO energy gap is provided. The crystal studied was refined as an inversion twin.

Crystal structure of 4-[(3-meth-oxy-2-oxidobenzyl-idene)azaniumyl]-benzoic acid methanol monosolvate

In the crystal of the title compound, C15H13NO4·CH3OH, the Schiff base mol-ecule exists in the zwitterionic form; an intra-molecular N-H⋯O hydrogen bond stabilizes the mol-ecular structure. The benzene rings are nearly co-planar, subtending a dihedral angle of 5.34 (2)°. In the crystal, classical O-H⋯O and weak C-H⋯O hydrogen bonds link the Schiff base mol-ecules and methanol solvent mol-ecules into a three-dimensional supra-molecular architecture. The crystal studied was refined as an inversion twin.

(E)-2-{[(2-Amino-phen-yl)imino]-meth-yl}-5-(benz-yl-oxy)phenol and (Z)-3-benz-yl-oxy-6-{[(5-chloro-2-hy-droxy-phen-yl)amino]-methyl-idene}cyclo-hexa-2,4-dien-1-one

The title Schiff base compounds, C20H18N2O2 (I) and C20H16ClNO3 (II), were synthesized from 4-benz-yloxy-2-hy-droxy-benzaldehyde by reaction with 1,2-di-amino-benzene for (I), and condensation with 2-amino-4-chloro-phenol for (II). Compound (I) adopts the enol-imine tautomeric form with an E configuration about the C=N imine bond. In contrast, the o-hy-droxy Schiff base (II), is in the keto-imine tautomeric form with a Z configuration about the CH-NH bond. Neither mol-ecule is planar. In (I), the central benzene ring makes dihedral angles of 46.80 (10) and 78.19 (10)° with the outer phenyl-amine and phenyl rings, respectively, while for (II), the corresponding angles are 5.11 (9) and 58.42 (11)°, respectively. The mol-ecular structures of both compounds are affected by the formation of intra-molecular contacts, an O-H⋯N hydrogen bond for (I) and an N-H⋯O hydrogen bond for (II); each contact generates an S(6) ring motif. In the crystal of (I), strong N-H⋯O hydrogen bonds form zigzag chains of mol-ecules along the b-axis direction. Mol-ecules are further linked by C-H⋯π inter-actions and offset π-π contacts and these combine to form a three-dimensional network. The density functional theory (DFT) optimized structure of compound (II), at the B3LYP/6-311+G(d) level, confirmed that the keto tautomeric form of the compound, as found in the structure determination, is the lowest energy form. The anti-oxidant capacities of both compounds were determined by the cupric reducing anti-oxidant capacity (CUPRAC) process.

Quantum mechanical and spectroscopic (FT-IR, FT-Raman) study, NBO analysis, HOMO-LUMO, first order hyperpolarizability and molecular docking study of methyl[(3R)-3-(2-methylphenoxy)-3-phenylpropyl]amine by density functional method

Quantum chemical techniques such as density functional theory (DFT) have become a powerful tool in the investigation of the molecular structure and vibrational spectrum and are finding increasing use in application related to biological systems. The Fourier transform infrared (FT-IR) and Fourier transform Raman (FT-Raman) techniques are employed to characterize the title compound. The vibrational frequencies were obtained by DFT/B3LYP calculations with 6-31G(d,p) and 6-311++G(d,p) as basis sets. The geometry of the title compound was optimized. The vibrational assignments and the calculation of Potential Energy Distribution (PED) were carried out using the Vibrational Energy Distribution Analysis (VEDA) software. Molecular electrostatic potential was calculated for the title compound to predict the reactive sites for electrophilic and nucleophilic attack. In addition, the first-order hyperpolarizability, HOMO and LUMO energies, Fukui function and NBO were computed. The thermodynamic properties of the title compound were calculated at different temperatures, revealing the correlations between heat capacity (C), entropy (S) and enthalpy changes (H) with temperatures. Molecular docking studies were also conducted as part of this study. The paper further explains the experimental results which are in line with the theoretical calculations and provide optimistic evidence through molecular docking that the title compound can act as a good antidepressant. It also provides sufficient justification for the title compound to be selected as a good candidate for further studies related to NLO properties.

Crystal structure of 2-{[(E)-(4-anilinophen-yl)iminium-yl]meth-yl}-5-(di-ethyl-amino)-phenolate

The title compound, C₂₃H₂₅N₃O, crystallized with one single mol­ecule in the asymmetric unit and present in the zwitterionic form. In the crystal, mol­ecules are connected by N—H⋯O hydrogen bonds generating –A–B–A–B– zigzag chains extending along [010]. The chains are linked via C—H⋯π inter­actions and π–π inter­actions [with a centroid–centroid distance of 3.444 (3) Å)] between the benzene ring and the imino group of symmetry-related mol­ecules, forming slabs lying parallel to (100).

The title compound, C₂₃H₂₅N₃O, crystallized with one single mol­ecule in the asymmetric unit and is present in the zwitterionic form. There is an intra­molecular N—H⋯O hydrogen bond in the mol­ecule with the phenol ring being inclined to the central benzene ring by 20.67 (14)°. The terminal amino­phenyl ring forms a dihedral angle of 54.21 (14)° with the central benzene ring. The two outer aromatic rings are inclined to one another by 74.54 (14)°. In the crystal, the mol­ecules are connected by N—H⋯O hydrogen bonds, with adjacent molecules related by a 2₁ screw axis, generating –A–B–A–B– zigzag chains extending along [010]. The chains are linked via C—H⋯π and π–π inter­actions [with a centroid–centroid distance of 3.444 (3) Å] between the benzene ring and the imino group of symmetry-related mol­ecules, forming slabs lying parallel to (100).

Crystal structure of N (1)-phenyl-N (4)-[(E)-(pyren-1-yl)methyl-idene]benzene-1,4-di-amine

In the title compound, C29H20N2, the dihedral angles subtended by the central p-phenyl-enedi-amine ring with respect to the mean plane of the terminal pyrenyl ring system (r.m.s. deviation = 0.027 Å) and the terminal N-phenyl ring are 29.34 (4) and 43.43 (7)°, respectively. The conformation about the C=N bond is E. In the crystal, mol-ecules are linked by N-H⋯π and C-H⋯π inter-actions forming chains propagating along the [10-2] direction. These chains are linked via π-π inter-actions [inter-centroid distances are in the range 3.5569 (11)-3.708 (1) Å], forming slabs lying parallel to (30-4).

Crystal structure of (E)-2-{[(4-anilinophen-yl)imino]-meth-yl}phenol

The title compound crystallized with two independent mol­ecules (A and B) in the asymmetric unit, which differ essentially in the orientation of the terminal amino­phenyl ring with respect to the central benzene ring. In the crystal, mol­ecules are linked via N—H⋯O hydrogen bonds forming –A-B–A–B– zigzag chains propagating along [010].

The title compound, C₁₉H₁₆N₂O, crystallized with two independent mol­ecules (A and B) in the asymmetric unit. There is an intra­molecular O—H⋯N hydrogen bond in each mol­ecule with the phenol ring being inclined to the central benzene ring by 4.93 (14) and 7.12 (14)° in mol­ecules A and B, respectively. The conformation of the two mol­ecules differs essentially in the orientation of the terminal amino­phenyl ring with respect to the central benzene ring; this dihedral angle is 50.51 (4)° in mol­ecule A and 54.61 (14)° in mol­ecule B. The two outer aromatic rings are inclined to one another by 51.39 (14) and 49.88 (14)° in mol­ecules A and B, respectively. In the crystal, mol­ecules are connected by N—H⋯O hydrogen bonds generating –A-B–A–B– zigzag chains extending along [010]. The chains are linked via C—H⋯π inter­actions involving neighbouring A mol­ecules, forming slabs lying parallel to (100).

Synthesis, characterization, and DFT studies of a new chiral ionic liquid from (S)-1-phenylethylamine

A new chiral ionic liquid was synthesized from (S)-1-phenylethylamine and it was studied by IR, Raman, polarimetry, NMR and X-ray crystal diffraction. Its vibrational spectral bands are precisely ascribed to the studied structure with the aid of DFT theoretical calculations. The optimized geometries and calculated vibrational frequencies are evaluated via comparison with experimental values. The vibrational spectral data obtained from IR and Raman spectra are assigned based on the results of the theoretical calculations by the DFT-B3LYP method at 6-311G(d,p) level. The computed vibrational frequencies were scaled by scale factors to yield a good agreement with observed experimental vibrational frequencies.The vibrational modes assignments were performed by using the animation option of GaussView5.0 graphical interface for Gaussian program.

N (1)-[(1H-Imidazol-2-yl)methyl-idene]-N (4)-phenyl-benzene-1,4-di-amine

The title compound, C16H14N4, is non-planar with dihedral angles between the planes of the imidazole and phenyl-enedi-amine rings of 30.66 (4)° and between the planes of the phenyl-enedi-amine and N-phenyl rings of 56.63 (7)°. In the crystal, mol-ecules are connected by N-H⋯N hydrogen bonds, generating a chain extending along the b-axis direction. The crystal structure is also stabilized by C-H⋯π inter-actions between N-phenyl and imidazole rings and slipped π-π stacking inter-actions between imidazole rings [centroid-centroid distance = 3.516 (4) Å] giving an overall two-dimensional layered structure lying parallel to (010).

An experimental and theoretical study of the vibrational spectra and structure of Isosorbide dinitrate

The present work aims at exploring the vibrational spectra of Isosorbide dinitrate and its chemical activity in a five membered ring system. The FT-IR and FT-Raman spectral studies of the Isosorbide dinitrate (ISDN) were carried out. The equilibrium geometry, various bonding features and harmonic vibrational frequencies of ISDN have been calculated using B3LYP density functional theory (DFT) with 6-31G(d,p) as basis set. The calculated HOMO and LUMO energies and density of states (DOS) show the chemical activity of the molecule. Good correlations between the experimental (1)H and (13)C NMR chemical shifts in methanol-d and calculated GIAO shielding tensors were found. The potential energy surface was studied using the DFT method.

The 'partial resonance' of the ring in the NLO crystal melaminium formate: study using vibrational spectra, DFT, HOMO-LUMO and MESP mapping

The molecular geometry and vibrational spectral investigations of melaminium formate, a potential material known for toxicity and NLO activity, has been performed. The FT IR and FT Raman spectral investigations of melaminium formate is performed aided by the computed spectra of melaminium formate, triazine, melamine, melaminium and formate ion, along with bond orders and PED, computed using the density functional method (B3LYP) with 6-31G(d) basis set and XRD data, to reveal intermolecular interactions of amino groups with neighbor formula units in the crystal, intramolecular H⋯H repulsion of amino group hydrogen with protonating hydrogen, consequent loss of resonance in the melaminium ring, restriction of resonance to N(3)C(1)N(1) moiety leading to special type resonance of the ring and the resonance structure of CO(2) group of formate ion. The 3D matrix of hyperpolarizability tensor components has been computed to quantify NLO activity of melamine, melaminium and melaminium formate and the hyperpolarizability enhancement is analyzed using computed plots of HOMO and LUMO orbitals. A new mechanism of proton transfer responsible for NLO activity has been suggested, based on anomalous IR spectral bands in the high wavenumber region. The computed MEP contour maps have been used to analyze the interaction of melaminium and formate ions in the crystal.

4-[(E)-(4-Eth-oxy-phen-yl)imino-meth-yl]phenol

In the title compound, C₁₅H₁₅NO₂, the dihedral angle between the benzene rings is 52.04 (5)° and the mol­ecule has an E conformation about the central C=N bond. In the crystal, mol­ecules are connected by O—H⋯N hydrogen bonds, forming zigzag chains along the b axis. The crystal packing also features weak C—H⋯O inter­actions.

(E)-4-[(4-Bromo-phen-yl)imino-meth-yl]-2-meth-oxy-phenol

In the crystal structure of the title compound, C₁₄H₁₂BrNO₂, the dihedral angle between the rings is 37.87 (10)° and the mol­ecule has an E conformation about the central C=N bond. In the crystal, mol­ecules are connected by inter­molecular O—H⋯N hydrogen bonds into zigzag chains running parallel to the b axis. The packing also features C—H⋯O inter­actions.