Structural, optical, dielectric, and quantum-chemical investigation of glycine phosphite nanocrystals for optoelectronic application

Abstract

Glycine phosphite (NH₃CH₂COOH·H₂PO₃) nanocrystals were synthesized through slow evaporation solution growth and rigorously analyzed for their optical, dielectric, and structural characteristics. X-ray diffraction validated a monoclinic structure (space group P2₁/c) with revised lattice parameters (a = 7.401 Å, b = 8.465 Å, c = 9.737 Å, β = 100.73°) and nanoscale crystallinity (43.5–90.1 nm). Microstrain values (0.00084–0.00211) and dislocation density (10¹⁴ lines/m²) demonstrated minimal lattice defects. The molecular stability of the –NH₃⁺, –COOH, and phosphate groups was confirmed using FTIR analysis, which identified their distinct vibrational signatures. The optical assessments confirmed the wide-bandgap dielectric properties, indicating direct and indirect band gaps of 5.32 eV and 5.24 eV, respectively. These findings highlight the material’s confirming strong UV transparency and excellent insulating behavior, with potential for high-frequency dielectric applications.

Quantum-chemical calculations were performed using density functional theory (DFT) at the B3LYP/6–311 +  + G(d,p) level with Gaussian 09 software. The computed HOMO–LUMO gap (5.27 eV) closely matched experimental values. Analyses of frontier molecular orbitals (FMO) and density of states (DOS) validated charge localization in accordance with insulating characteristics. NBO analysis revealed strong intermolecular charge transfer interactions [LP(2)O → π [(C = 0)], with stabilization energies reaching 56.8 kcal/mol, indicating improved electric delocalization and molecular stability. The Mulliken charge distribution showed strong polarization (P11: + 1.089e; O14: − 0.903 e), resulting in a dipole moment of 3.99 Debye. These findings show that hydrogen-bond-assisted charge transfer and polarization are the primary drivers of improved dielectric and optical performance. The global reactivity descriptors of chemical hardness (2.64 eV), electrophilicity index (1.94 eV), and electronegativity (3.20 eV) confirmed the experimental results of structural stability and wide-bandgap dielectric properties. Glycine phosphite nanocrystals outperform α-/γ-glycine and triglycine sulfate in UV transparency and band gap, suggesting their potential as advanced dielectric materials. These nanocrystals exhibit strong dielectric and UV-transparent properties.