Synthesis, structural, DFT computation, and nonlinear absorption studies of DL-methioninium maleate

DL-Methioninium maleate (DLMM) crystals were developed via slow evaporation and underwent thorough physicochemical and nonlinear optical characterization. Single-crystal XRD confirmed DLMM’s monoclinic structure with a P2₁/c space group. Hirshfeld surface and 2D fingerprint analyses evaluated intermolecular interactions. DFT/B3LYP computations with a 6-311G +  + (d,p) basis set authenticated simulated FT-IR and FT-Raman spectra, revealing N–H⋯O hydrogen bonding. Frontier molecular orbital analysis indicated charge transfer within the molecule, while natural bond orbital analysis examined stabilization interactions. UV–vis studies showed maximum absorbance at 216 nm and high transmittance from 340 to 800 nm. Photoluminescence revealed bluish emission peaks at 419, 433, and 486 nm. Z-scan studies with a nano-pulsed Nd:YAG laser demonstrated DLMM’s optical limiting behavior via two-photon absorption, with a nonlinear absorption coefficient of 0.41 × 10^–10 m/W and an onset threshold of 4.12 × 10^–12 W/m², indicating potential for laser safety devices.