Growth, Structural Characterization, and Nonlinear Optical Properties of L-Lysinium Hydrogen Adipate Single Crystals: An Integrated Experimental and DFT Study
Year: 2026
Type: article
Abstract: The proton-transfer salt L-lysinium hydrogen adipate (LLA) was obtained as single crystals by slow evaporation from an aqueous solution at room temperature. It comprises the natural amino acid L-lysine in its cationic form together with adipic acid as the diacid component. LLA crystallizes in the non-centrosymmetric (NCS) monoclinic space group P21, the symmetry required for bulk second-harmonic generation (SHG). Powder XRD confirmed phase purity. Hirshfeld surface analysis quantified the intermolecular contacts that stabilize the NCS packing, showing that N–H···O and O–H···O hydrogen bonds together contribute 45.8% of the Hirshfeld surface area. The Kurtz–Perry powder method showed an SHG efficiency 1.2 times that of potassium dihydrogen phosphate (KDP) under Q-switched Nd:YAG laser excitation (λ = 1064 nm). The LLA crystal exhibits thermal stability up to 150 ºC and a distinct melting endotherm at 203 ºC. Density functional theory (DFT) calculations at the B3LYP/6-31+G (d,p) level yielded a HOMO-LUMO gap of 5.34 eV, indicating favourable electronic and charge-transfer characteristics for NLO behaviour. Natural bond orbital (NBO) analysis attributed the NLO response primarily to LP→π*/σ* interactions at the carboxylate termini (E(2) up to 113.03 kcal mol-1). The calculated first hyperpolarizability (βtotal = 460.79 × 10-30 esu, approximately 795 times that of urea) is consistent with the experimental SHG efficiency. Taken together, the experimental and computational results position LLA as a viable organic material for frequency-doubling and photonic device applications.
DOI: 10.54392/irjmt26419
Field: Materials Science
Domain: Physical Sciences
Open Access status: diamond
OpenAlex ID: W7171990972