Density functional theory studies on molecular structure and vibrational spectra of NLO crystal l-phenylalanine phenylalanium nitrate for THz application

Synthesis, crystal structure, spectroscopic and computational studies of NLO active 2-methylimdazolium 4-nitrobenzoic acid single crystal

In this report, we have presented the theoretical and experimental investigation of 2-Methylimdazolium 4-Nitrobenzoic Acid (2MI4NB) - an organic crystal. The good quality 2MI4NB single crystal was grown by slow evaporation technique. Both single and powder X-ray diffraction (XRD) analysis confirmed that the grown crystal structure is Triclinic with the P1 space group. The vibrational modes present in the chemical were validated through Fourier transform infrared (FT-IR) spectrum investigations. Density functional theory (DFT), a quantum chemical approach, has emerged as a potential or an effective tool for studying molecular structure and NLO properties and is being used frequently in applications involving NLO systems. HOMO-LUMO analysis and reactivity parameters were calculated. Molecular Electrostatic Potential (MEP), Natural Bond Orbital (NBO) analysis and first order hyper polarizability were studied by B3LYP theoretical level with 6-311++G(d,p) basic set. In addition, the Mulliken Atomic Charge was calculated with the same basic set. The thermal properties of the 2MI4NB crystal was analysed by TG-DTA studies. It shows that the two endothermic peaks were observed. The optical absorption spectrum shows that there is no absorption in the region of 430-1200 nm. The Z-scan analysis gives the third order NLO properties like refractive index and third-order NLO susceptibility of 2MI4NB crystals.

Crystal structure, Hirshfeld surfaces and DFT computation of NLO active (2E)-2-(ethoxycarbonyl)-3-[(1-methoxy-1-oxo-3-phenylpropan-2-yl)amino] prop-2-enoic acid

Nonlinear optical (NLO) activity of the compound (2E)-2-(ethoxycarbonyl)-3-[(1-methoxy-1-oxo-3-phenylpropan-2-yl)amino] prop-2-enoic acid is investigated experimentally and theoretically using X-ray crystallography and quantum chemical calculations. The NLO activity is confirmed by both powder Second Harmonic Generation (SHG) experiment and first hyper polarizability calculation. The title compound displays 8 fold excess of SHG activity when compared with the standard compound KDP. The gas phase geometry optimization and vibrational frequencies calculations are performed using density functional theory (DFT) incorporated in B3LYP with 6-311G++(d,p) basis set. The title compound crystallizes in non-centrosymmetric space group P21. Moreover, the crystal structure is primarily stabilized through intramolecular N-H···O and O-H···O hydrogen bonds and intermolecular C-H···O and C-H···π interactions. These intermolecular interactions are analyzed and quantified using Hirshfeld surface analysis and PIXEL method. The detailed vibrational assignments are performed on the basis of the potential energy distributions (PED) of the vibrational modes.

Molecular structure, vibrational spectra, NBO, UV and first order hyperpolarizability, analysis of 4-Chloro-dl-phenylalanine by density functional theory

The Fourier transform infrared (4000-400cm(-1)) and Fourier transform Raman (3500-50cm(-1)) spectra of 4-Chloro-dl-phenylalanine (4CLPA) were recorded and analyzed. The equilibrium geometry, bonding features and harmonic vibrational wavenumbers were investigated with the help of density functional theory (DFT) method using B3LYP/6-31G(d,p) as basis set. The observed vibrational wavenumbers were compared with the calculated results. Natural bond orbital analysis confirms the presence of intramolecular charge transfer and the hydrogen bonding interaction. Predicted electronic absorption spectra from TD-DFT calculation have been analyzed comparing with the UV-Vis (200-800nm) spectrum. The effects of chlorine and ethylene group substituent in benzene ring in the vibrational wavenumbers have been analyzed. The HOMO-LUMO energy gap explains the charge interaction taking place within the molecule. The first order hyperpolarizability (β0) and related properties (β, α0 and Δα) of 4CLPA were calculated. The Chemical reactivity and chemical potential of 4CLPA is calculated. In addition, molecular electrostatic potential (MEP), frontier molecular orbital (FMO) analysis were investigated using theoretical calculations.