Synthesis, XRD analysis, FTIR and Raman spectroscopy, Hirshfeld surface analysis and density functional theory of NLO material L-phenylalanine L-phenylalaninium malonate

Abstract

L-phenylalanine l-phenylalaninium malonate (LPLPM) single crystal is considered one of the amino-based nonlinear optical materials for applications in the optoelectronics field. It was grown using a slow evaporation method at room temperature. Single crystal XRD studies have confirmed that the grown crystal belongs to a monoclinic structure with non-centrosymmetric space group P2₁. The lattice parameters of the grown crystal were found to be as a = 14.02 Å (4), b = 5.40 Å (10), c = 14.61Å (4) and α = γ = 90°, β = 107.41° (3) and V = 1075.6 ų (4). The molecular structure and crystal system were also carefully examined using single crystal and powder XRD investigations. The FTIR and Raman spectra were recorded and analyzed for the confirmation of functional groups and the corresponding vibrational modes. Density functional theory (DFT) calculations of the sample have been done to determine the optimized geometry of the material from vibrational assignments. The optimized geometrical parameters obtained from the DFT calculations match well with the experimentally obtained results of FTIR and Raman spectral studies. Frontier molecular orbital analysis was performed to understand the electronic structure and the reactivity of molecules. The energy gap of the compound was found to be 6.0632 eV from the HOMO-LUMO analysis. The higher value of total first hyperpolarizability β_tot = 146.784 × 10⁻³¹ e.s.u. reflects the potential of the material for the nonlinear optical response. An attempt has been made to study Hirshfeld surface analysis of the crystal structure to gain deeper insight into the intermolecular interactions present among the molecules. Kurtz and Perry powder technique confirmed the nonlinear optical property of the material and the second harmonic generation efficiency of the LPLPM was found to be 0.4 times that of standard material KDP. The various characterization studies of LPLPM are very interesting in understanding the physico-chemical properties of the material LPLPM for technological applications. Furthermore, NBO analyses, Fukui function and Mulliken population analysis of LPLPM were included to understand the chemical parameters, inter-molecular interactions and the reactivity of the compound in the supplementary material section.