Growth, experimental and theoretical investigation on the nonlinear optical, vibrational, and electronic properties of L-2-aminobutyric acid D-methionine crystal: a combined experimental and quantum chemical approach

Single crystals of L-2-aminobutyric acid D-methionine (LABADM) with optical activity have been grown by the slow evaporation method from a solution of L-2-aminobutyric acid D-methionine and water. The thermal stability and melting point of the crystal grown were ascertained via TGDTA analysis. In this investigation, the Fourier transform infrared spectra of LABADM in its solid form were recorded and analysed. The ab initio Hartree–Fock and density functional theory (DFT/B3LYP) methods were employed to conduct theoretical calculations on the optimised molecular structure, HOMO–LUMO, molecular electrostatic potential surfaces, nonlinear optical Mulliken charges, and vibrational studies for LABADM. These calculations were carried out using the 6–311+G(d,p) basis set. The density functional theory (DFT/B3LYP) methods with a 6–311+G(d,p) basis set were employed to carry out UV‒Vis analysis for LABADM. The potential for charge transfer within the molecule is indicated by the small HOMO–LUMO energy gap. NBO analysis confirmed the presence of intermolecular O–N…H hydrogen bonds resulting from the interaction between the lone pair of oxygen and the antibonding orbital. The non-covalent interaction revealed charge transfer between LABA and DM. The density of states (DOS) provided for the charge transfer behavior of electrons in the materials.