Nonlinear optical properties and structural characterization of a series of carboxyanilinium hydrogen selenite hybrids: Synthesis, first-principles calculations and correlation analysis for advanced photonic applications

Abstract

The exploration of novel nonlinear optical (NLO) materials is essential for advancing photonic and optoelectronic technologies. Within this context, we report in this work, the synthesis, crystallization, and NLO properties of three novel semi-organic compounds: o-carboxyanilinium hydrogen selenite (1), m-carboxyanilinium hydrogen selenite (2), and p-carboxyanilinium hydrogen selenite (3). These compounds were synthesized using an aqueous-phase grafting technique, producing distinct crystalline structures: monoclinic P21 for 1, monoclinic P21/n for 2, and triclinic P1¯ for 3. Single crystal X-ray diffraction revealed unique intra- and intermolecular interactions with significant implications for their optical properties. UV–Vis spectroscopy indicated broad absorption bands, varying among the compounds, and NLO measurements showed remarkable third harmonic generation (THG) and second harmonic generation (SHG) efficiencies, particularly for 1. First-principles calculations using DFT were performed to gain deeper insights into the structure–property relationship of these hybrids. These calculations confirmed the significant THG and SHG responses of 1 due to its favorable electronic structure and intermolecular interactions. Additionally, Bond Valence Sum (BVS) calculations were conducted to confirm the valence state of selenium in the HSeO3− anion, further supporting the structural integrity and stability of the compounds. HS analysis, combined with a meticulous examination of structure–property relationships, elucidated the role of H-bonding and π–π interactions in stabilizing the crystal lattice and underscored the critical influence of crystal symmetry, molecular conformation, and intermolecular interactions on the NLO performance. These findings offer valuable insights into the structural attributes and nonlinear susceptibilities of these hybrids. This work provides a deeper understanding of the design and behavior of semi-organic materials regarding their nonlinear optical properties.