Exploring the nonlinear optical properties of hypoxanthinium salts: a structural and computational analysis

In this study, we detail the synthesis and crystallographic characterization of an unprecedented structure, specifically hypoxanthinium chloride monohydrate ((I) hereafter), which crystallizes in the monoclinic P2₁/c space group. A comparative analysis was conducted with four related hypoxanthinium salts: hypoxanthinium bromide monohydrate (II), 9-methylhypoxanthinium chloride monohydrate (III), hypoxanthinium nitrate monohydrate (IV), and hypoxanthinium perchlorate monohydrate (V). This analysis has focused mainly on their crystal packing, hydrogen-bonding networks, and non-classical intermolecular interactions, as elucidated by comprehensive Hirshfeld surface and topological analyses. Theoretical investigation of the nonlinear optical (NLO) properties of the hypoxanthinium derivatives (I-V) was performed using the Density Functional Theory (DFT).

The crystalline environment was simulated using the iterative Supermolecule method (SM), and the static and dynamics linear refractive index, linear polarizability, second-order hyperpolarizability, and the third-order nonlinear susceptibility at the DFT/CAM-B3LYP/6-311++G(d,p) level were computed. The results for the macroscopic third-order nonlinear susceptibility of (II) was found to equal $$ . By replacing the bromine atom in (II) with a chlorine atom as in (III), the $$ value will be multiplied by 2.16, and therefore these results are large enough to suggest the potential application of these crystals as NLO materials.