Exploring the molecular geometry, Hirshfeld surface analysis, vibrational assignments, UV–Vis and Z-scan studies of a potential NLO material for photonic applications

Creatine Monohydrate (CMH), a novel organic nonlinear optical (NLO) crystal, was successfully synthesized and grown using the Slow Evaporation Solution Technique (SEST). Single-crystal X-ray diffraction revealed that CMH crystallizes in the monoclinic system with space group P2₁/c and lattice parameters: a = 12.310(2) Å, b = 5.091(7) Å, c = 12.543(2) Å, and β = 109.12(3)°, with a unit cell volume of 742.70 Å3. Vibrational analyses using FT-IR and FT-Raman spectroscopy showed excellent agreement with DFT/B3LYP/6–31 +  + G(d,p) calculations. Hirshfeld surface analysis quantified intermolecular interactions, revealing that H···H and O···H contacts dominate the crystal packing with contributions of 49.1% and 20.9%, respectively. Frontier molecular orbital (FMO) analysis indicated a HOMO–LUMO energy gap of 4.9251 eV, while the UV–Vis absorption maximum was observed at 276 nm, closely matching the TD-DFT predicted value of 294.06 nm. The computed hyperpolarizability (β₀) was 5.309 × 10−23esu, confirming CMH’s strong NLO response. Z-scan measurements at 532 nm exhibited reverse saturable absorption (RSA) behavior driven by a two-photon absorption process, with an effective nonlinear absorption coefficient of − 2.46 × 1012 W/m2 and an optical limiting threshold of 4.42 × 1012 W/m2. These findings affirm CMH’s potential for photonic and laser protection applications.