NIR-FT Raman Spectra Research Articles

Growth, effect of protonation and hydrogen bonding interactions of L-Histidine nitrate monohydrate, a potential semi organic third order nonlinear optical material

Single crystal of l-Histidine Nitrate monohydrate (LHNM) has been grown from aqueous solution by evaporation technique. A comprehensive investigation of the NIR FT-Raman and FT-IR spectra was carried out with the aid of normal coordinate analysis following the scaled quantum mechanical force field methodology supported by the density functional theory (DFT) computations to analyze the effects of intramolecular charge transfer on the geometries and the vibrational modes contributing to the linear electro-optic effect of the organic NLO material. Effect of protonation and hydrogen bonding interactions has been analyzed using structural analysis, natural bond orbital analysis, and spectral analysis. The HOMO-LUMO energy gap value suggests the possibility of charge transfer within the molecule. Hyperconjugative interactions responsible for second hyperpolarizabilities have been described by NBO and AIM analyses. Hirshfeld surface analysis reveals that the van der Waals H⋯H (32.3%) contact plays a significant role in crystal packing and that a variety of NH⋯O intermolecular contacts and hydrogen bonds leads to the formation of intermolecular charge transfer occurring in LHNM. The nonlinear refractive index (n2), nonlinear absorption coefficient (β) and third-order nonlinear susceptibility (χ3) of LHNM have been determined by Z-scan technique, which points to its potential application in the field of optical limiting. The calculated value of laser damage threshold was 2.04 GW/cm2.

Structural conformations and density functional study on the intramolecular charge transfer based on vibrational spectra of 2,4-dihydroxy-N′-(4-methoxybenzylidene)benzohydrazide

The NIR-FT Raman and FT-IR spectra of 2,4-dihydroxy-N′-(methoxybenzylidene) benzohydrazide (DMBBH) molecule have been recorded and analyzed. Density functional theory (DFT) calculations at the B3LYP/6-31G(d) level has been used to compute energies of different conformers of DMBBH to find out their stability, the optimized geometry of the most stable conformer and its vibrational spectrum. Information about the size, shape, charge density distribution and site of chemical reactivity of the molecules has been obtained by mapping electron density isosurface with electrostatic potential surfaces (ESP). A complete vibrational analysis has been attempted on the basis of experimental infrared and Raman spectra and calculated vibrational modes and potential energy distribution over the internal coordinates. The vibrational analysis confirm the charge transfer interaction between the phenyl rings through CNN skeleton. The broadening of the band at 1631cm−1 and the appearance of the band at 1556cm−1 strongly suggests the existence of proton equilibrium.

DFT computation and experimental analysis of vibrational and electronic spectra of phenoxy acetic acid herbicides

An absolute vibrational analysis has been attempted on the basis of experimental FTIR and NIR-FT Raman spectra with calculated vibrational wavenumbers and intensities of phenoxy acetic acids. The equilibrium geometry, bonding features and harmonic vibrational wavenumbers have been calculated with the help of B3LYP method with Dunning correlation consistent basis set aug-cc-pVTZ. The electronic structures of molecular fragments were described in terms of natural bond orbital analysis, which shows intermolecular OH⋯O and intramolecular CH⋯O hydrogen bonds. The electronic absorption spectra with different solvents have been investigated in combination with time-dependent density functional theory calculation. The pKa values of phenoxy acetic acids were compared.

Vibrational spectra, structural conformations, scaled quantum chemical calculations and NBO analysis of 3-acetyl-7-methoxycoumarin

The powder form NIR-FT Raman and FT-IR spectra of 3-acetyl-7-methoxycoumarin (3A7MC) have been recorded in the regions 4000–400 and 3500–100cm−1, respectively. The equilibrium geometry, vibrational frequencies, band intensities, NMR spectra, NBO analysis and UV–Vis spectral studies of the most stable conformer have been calculated by density functional B3LYP method with the 6-311G(d,p) basis set. A complete vibrational analysis has been attempted on the basis of experimental infrared and Raman spectra, the calculated wavenumber and intensity of the vibrational bands and the potential energy distribution over the internal coordinates. Information about the size, shape, charge density distribution and site of chemical reactivity of the molecules has been obtained by mapping the electron density isosurface with electrostatic potential surfaces (ESP). Natural bond orbital analysis has been carried out to understand the nature of different interactions responsible for the electron delocalization and the intramolecular charge transfer between the orbitals (n→π∗, n→σ∗, π→π∗).

Spectroscopic investigation and hydrogen-bonding analysis of triazinones

NIR FT-Raman, FTIR and UV-vis spectra of the herbicide metamitron were recorded and analyzed. The aromaticities, equilibrium geometries, bonding features, electrostatic potentials, and harmonic vibrational wavenumbers of the monomers and dimers of triazinone derivatives were also investigated with the aid of BLYP/6-311 G(df, p) density functional theory. Features in the vibrational spectra were assigned with the aid of the VEDA.4 program. The calculated results were a good match to the experimental data obtained from FTIR, Raman, and electronic absorption spectra. Mulliken population analysis was performed on the atomic charges and the HOMO-LUMO energies were also calculated. NBO analysis highlighted the intra- and intermolecular N-H…O and C-H…O hydrogen bonds in the crystal structures of the triazinones. The solvent effect was calculated using time-dependent density functional theory in combination with the polarizable continuum model.

DFT-based molecular modeling, NBO analysis and vibrational spectroscopic study of 3-(bromoacetyl)coumarin

The NIR-FT Raman and FT-IR spectra of 3-(bromoacetyl)coumarin (BAC) molecule have been recorded and analyzed. Density functional theory (DFT) calculation of two BAC conformers has been performed to find the optimized structures and computed vibrational wavenumbers of the most stable one. The obtained vibrational wavenumbers and optimized geometric parameters were seen to be in good agreement with the experimental data. Characteristic vibrational bands of the pyrone ring and methylene and carbonyl groups have been identified. The lowering of HOMO–LUMO energy gap clearly explains the charge transfer interactions taking place within the molecule.

DFT computations and spectroscopic analysis of a pesticide: Chlorothalonil

NIR FT-Raman and IR spectra of the biologically active molecule, chlorothalonil have been recorded and analyzed. The molecular geometry and vibrational wavenumbers of the title compound in the ground state have been calculated by density functional theory (DFT) with 6-31G(d) basis set. In order to obtain the information about the influence of intramolecular interaction on the molecule, the calculated geometries of chlorothalonil molecule was compared with the experimental data. The results of the optimized molecular structure gave clear evidence for the intramolecular charge transfer (ICT). Time-dependent density functional theory (TD-DFT) calculation of the electronic spectra has been performed and compared with the experimental UV–visible spectrum. Mulliken's net charges have been calculated and compared with the atomic natural charges. The effects of chlorine and cyanide group substituent in benzene ring in the vibrational wavenumbers have been analyzed. NBO analysis is useful to understand the intramolecular hyperconjugative interaction between lone pair Cl and σ*(C–C) bond orbital.

Structural conformations and vibrational spectral study of chloroflavone with density functional theoretical simulations

NIR-FT Raman and FT-IR spectra of 6-chloroflavone were recorded and analyzed. The vibrational wavenumber of the compound have been computed using B3LYP/6-31++G(d,p) level to derive the equilibrium geometry, conformational stability, molecular orbital energies and vibrational wavenumbers. The carbonyl stretching vibrations have been lowered due to conjugation and hydrogen bonding in the molecules. The assignment of fundamental vibrations agrees well with the calculated wavenumbers.

Efficient π-electron conjugated push–pull nonlinear optical chromophore 1-(4-methoxyphenyl)-3-(3,4-dimethoxyphenyl)-2-propen-1-one: A vibrational spectral study

As part of the efforts for the design new organic nonlinear optical (NLO) materials with high efficiency for present day technological requirements, a comprehensive investigation on the intramolecular charge transfer (ICT) of an efficient π-conjugated potential push–pull NLO chromophore, 1-(4-methoxyphenyl)-3-(3,4-dimethoxyphenyl)-2-propen-1-one to a strong electron acceptor group through the π-conjugated bridge has been carried out from their vibrational spectra. The NIR FT-Raman and FT-IR spectra supported by the density functional theory (DFT) quantum chemical computations have been employed to analyze the effects of intramolecular charge transfer on the geometries and the vibrational modes contributing to the linear electro-optic effect of the organic NLO material. The calculated first hyperpolarizability of DMMC is 6.650 × 10 −30 esu, which is 25 times that of urea. The simultaneous IR and Raman activation of the phenyl ring modes of ν(C C/C–C) mode, ring C C stretching modes, in-plane deformation modes and the umbrella mode of methyl groups also provide evidences for the charge transfer interaction between the donors and the acceptor group through the π-system. Vibrational analysis indicates the electronic effects such as induction and back-donation on the methyl hydrogen atoms causing the lowering of stretching wavenumbers have also been analyzed in detail. The planar conformations would give an enhanced NLO activity where as any deviations from planarity would decrease the mobility of electrons within the π-conjugated molecular system, resulting a reduction in NLO activity.

Efficient π electrons delocalization in prospective push–pull non-linear optical chromophore 4-[ N, N-dimethylamino]-4′-nitro stilbene (DANS): A vibrational spectroscopic study

A comprehensive investigation on the intramolecular charge transfer (ICT) of an efficient π-conjugated potential push–pull NLO chromophore, 4-[ N, N-dimethylamino]-4′-nitro stilbene (DANS), from a strong electron-donor group (dimethylamino- N(CH 3) 2) to a strong electron-acceptor group (nitro-NO 2) through the π-conjugated bridge ( trans-stilbene) has been carried out from their vibrational spectra. The NIR FT-Raman and FT-IR spectra supported by the density functional theory (DFT) quantum chemical computations have been employed to analyze the effects of intramolecular charge transfer on the geometries and the vibrational modes contributing to the linear electro-optic effect of the organic NLO material. It has been observed that the changes in the endocyclic and exocyclic angles result from the charge-transfer interaction of the phenyl ring and the amino group in the electron-donor side of the NLO chromophore. The strongest vibrational modes contributing to the electro-optic effect have been identified and examined from the concurrent IR and Raman activation of ν(C C/C–C) mode, ring C C stretching modes, in-plane deformation modes, nitro modes and the umbrella mode of methyl groups. Furthermore, the splitting of the vinyl stretching modes and the electronic effects such as hyperconjugation and backdonation on the methyl hydrogen atoms causing the decrease of stretching frequencies and infrared intensities have also been analyzed in detail. The effect of frontier orbitals transition of electron density transfer and the influence of planarity between the phenyl rings of the stilbene moiety on the first hyperpolarizability have also been discussed.

Natural bond orbital analysis and vibrational spectroscopic studies of H-bonded N, N′-diphenylguanidinium nitrate

NIR-FT Raman and FT-IR spectra of the crystallized biologically active molecule N, N′-diphenylguanidinium nitrate (DGN) have been recorded and analyzed using quantum chemical computations based on density functional theory. The extraordinary basicity and strong stability of this novel bioactive compound has been discussed as the consequence of resonance stabilization leading to Y-aromaticity and hydrogen bonding. This peculiar Y-delocalization character of DGN is well reflected in the optimized geometry and bond order (BO) calculations. The observance of the equality of C–N bond lengths in the protonated species indicates delocalization of the π-electron system. The spectroscopic and natural bonds orbital (NBO) analysis confirms the occurrence of strong network of inter molecular hydrogen bonds. The changes in electron density in the global minimum and in the energy of hyperconjugative interactions of DGN calculated by second order perturbation theory have been studied extensively in comparison with the values of the neutral species. The observed characteristic ring vibrations are well fit with the theoretical values calculated at B3LYP/6-31G∗ level.

Vibrational spectra and ab initio computations of sarcosinium oxalate monohydrate

Single crystals of sarcosinium oxalate monohydrate (SOM) are grown by the slow-evaporation technique at ambient temperature, and vibrational spectroscopic analysis is carried out using NIR-FT Raman, FT-IR, and SERS spectra. The normal mode frequencies and corresponding vibrational analysis of SOM are examined theoretically using the Gaussian’98 set of quantum chemical codes. The two bands present in the SOM ν C=O region, clearly observed in the Raman spectrum, are assigned to “free” and “bonded” carbonyl groups with the hydrogen atom. Vibrational analysis indicates the presence of C-H—O hydrogen bonding interaction producing a blueshift of the C-H stretching frequency.

Structural and electronic contributions to hyperpolarizability in methyl p-hydroxy benzoate

The single crystals of methyl p-hydroxy benzoate (MPHB) are grown from methanol solution by a low temperature solution growth technique. The SHG efficiency is tested using Q-switched Nd:YAG laser of wavelength λ at 1064 nm, which is approximately 1.2 times that of urea. Vibrational spectral analysis using NIR-FT Raman and FT-IR spectra is carried out to understand the structural and electronic contributions to hyperpolarizability in MPHB. The DFT computations are also performed at B3LYP/6-311G(d,p) level to derive equilibrium geometry, vibrational wavenumbers and intensities. The results of ab initio calculations at HF/6-311G(d,p) level show that the vibrational contribution for the second-order electro-optic coefficient in MPHB is about 19.5%. Vibrational spectral studies also provide evidence for the charge transfer interaction between the donors and the acceptor group through the π-system. The π-electron cloud movement from donor to acceptor can make the molecule highly polarized and the intramolecular charge transfer interaction must be responsible for the nonlinear optical properties of MPHB. The splitting of the carbonyl mode may be attributed to the intramolecular association based on C O⋯H type hydrogen bonding in the molecule. The conjugation and influence of intermolecular hydrogen bonding (C O⋯H) type network in the crystal results in lowered C O stretching wavenumber.

Yb 3+ as an origin of the strong anti-Stokes luminescence in NIR FT-Raman spectra of some lanthanide sesquioxides

Strong anti-Stokes bands observed in FT-Raman spectra of Y 2O 3, Gd 2O 3 and Lu 2O 3 are explained by NIR luminescence of Yb 3+ impurities present in sesquioxides after the excitation with the 1064 nm line of an Nd:YAG laser. Samples of Y 2O 3:Yb, Ga 2O 3:Yb, CeO 2:Yb, Gd 2O 3:Yb and Lu 2O 3:Yb were prepared by solution combustion synthesis procedure using urea. All materials were investigated by FT-Raman and FT-NIR spectroscopy and characterized by X-ray powder diffraction.

Vibrational spectra and density functional theoretical calculations on the antitumor drug, plumbagin

Plumbagin is a potential toxic antitumor drug extracted from Plumbago rosea. Vibrational spectral analysis of plumbagin is carried out using NIR-FT Raman and FT-IR spectra. The DFT computations are also performed at B3LYP/6-31G (d,p) level to derive equilibrium geometry, vibrational wavenumbers, intensities and atomic charges. Optimized geometry reveals that the contraction of C12O16 and C13C14 bonds is due to the increase in the electron donating ability of the CH3 group. Vibrational analysis is used to investigate the electronic effects of hyperconjugation and induction of the methyl group with the π orbital of an aromatic ring system and resulting increase of stretching mode wavenumbers and decrease of infrared intensities. The splitting of the carbonyl modes might be attributed to structural and functional asymmetry in the carbonyl groups and intermolecular association based on CO···H-type hydrogen bonding in the molecule. In a hydrogen-bonded carbonyl, resonance can occur, which puts a partial negative charge on the oxygen atom accepting the hydrogen bond and a positive charge on the atom donating the hydrogen. The resulting partial ‘transfer of allegiance’ of the proton enhances resonance and lowers the C15O19 stretching wavenumber. It is inferred that this mechanism plays an important role in the biological activity of PLBN. Condensation of the two ring systems disturbs the benzene ring slightly, which gives rise to a shift in those modes to the lower wavenumbers. Copyright © 2005 John Wiley & Sons, Ltd.

Non-vibrational features in NIR FT-Raman spectra of lanthanide sesquioxides

In this Letter, we report the FT-Raman and FT-NIR spectra of all lanthanide sesquioxides and yttrium sesquioxide. The majority of lanthanide sesquioxides and yttrium sesquioxide show additional bands in FT-Raman spectra (after the excitation with the 1064 nm line of a Nd:YAG laser) that cannot be explained by vibrational origin. Additional bands in the FT-Raman spectra of heavy lanthanide sesquioxides appear in the Stokes region of the spectrum, but there are also some very strong unexpected bands in the anti-Stokes region of some light lanthanide sesquioxides and in yttrium sesquioxide, notably around 800 and 1100 cm −1. The non-vibrational bands present in FT-Raman spectra of lanthanide sesquioxides and yttrium sesquioxide are not seen in published Raman spectra with visible excitation. A possible origin of these additional bands is in luminescence of lanthanide ions.

NIR-FT Raman and infrared spectra and ab initio computations of glycinium oxalate

The single crystals of glycinium oxalate are grown by slow evaporation technique and vibrational spectral analysis is carried out using NIR-FT Raman and FT-IR spectra. The ab initio quantum computations are also performed at HF/6–31 G(d) level to derive the optimized geometry, atomic charges and vibrational frequencies of the glycinium oxalate molecule. Vibrational analysis indicates the presence of peculiar intermolecular CH⋯O hydrogen bonding interaction producing ‘blue shift’ of CH stretching frequency. The vibrational spectra confirm the existence of NH 3 + in glycinium oxalate. Hydroxyl vibrations with different inter and intra molecular H-bonding are analysed, supported by computed results.

Vibrational spectroscopic studies on the natural product, columbianadin

NIR-FT Raman and FT-IR spectra of columbianadin, extracted from seeds and roots of Heracleum candolleaum, were recorded and analyzed. The vibrational frequencies of the compound have been computed using semi-empirical AM1 method and compared with experimental values. The CO stretching frequencies of the carbonyl groups have been lowered due to conjugation. The CH stretching and bending vibrations of CH 3 groups of the ester part indicate the presence of hyperconjugation effect. Characteristic ring vibrations have also been identified.

NIR FT Raman Spectroscopy–a Rapid Analytical Tool for Detecting the Transformation of Cellulose Polymorphs

This is a report of the combined use of NIR FT Raman spectroscopy and X-ray diffraction measurements (WAXS) to investigate the polymorphic transformation of cellulose I into cellulose II. For this reason samples of cellulose I were swelled in different concentrations of NaOH and dissolved in different molten inorganic salts hydrates (LiCl·2ZnCl2·6H2O, LiClO4·3H2O, LiSCN·2,5H2O and ZnCl2·4H2O). NIR FT Raman spectra of the alkali treated samples were recorded. They characterize the pure modifications cellulose I and II as well as mixtures of the two polymorphic phases. The results of the Raman measurements were confirmed by X-ray scattering. The paper demonstrates that FT Raman vibrational spectroscopy is a powerful, rapid analytical method which may be used to follow the polymorphic transformation of cellulose I into cellulose II.

NIR FT Raman spectroscopic studies of η-Al 2O 3 and Mo/η-Al 2O 3 catalysts

NIR FT Raman spectra excited at 1064 nm have been obtained from samples of Mo/η-Al 2O 3 catalysts after treatment at 773 K in vacuum for 12 h. The samples were heated in quartz tubes which were sealed and transferred directly to the spectrometers without exposure to the ambient atmosphere. The broad background previously observed in the NIR FT Raman spectra of hydrated Mo/η-alumina samples disappeared after the dehydration. Upon exposure to ambient air the broad background signal reappeared suggesting that the broad background feature can be attributed to surface hydroxyl groups present in the hydrated samples. Furthermore, it was observed that upon treating the η-Al 2O 3 with water the broad background signal disappeared and the presence of bayerite (Al(OH) 3) or boehmite (AlO(OH)) was detected depending on the experimental details. The identification of the various phases is supported by XRPD analysis. The overall conclusion is that the broad NIR FT Raman background can be attributed to surface hydroxyl groups in hydrated η-Al 2O 3.