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 \({{\chi }^{3}=0.81 \times 10}^{-20}{m}^{2}/{V}^{2}\) ${{\chi }^3=0.81\times 10}^{-20}{m}^2/V^2$ . By replacing the bromine atom in (II) with a chlorine atom as in (III), the \({\chi }^{3}\) ${\chi }^3$ 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.