Exploring the influence of charge transfer interactions on third-order optical nonlinearity, physicochemical characterization and optical limiting behaviour of (4-Methoxyphenyl) methanaminium chloride single crystal for photonic applications

A protonated third-order nonlinear optical crystal, (4-Methoxyphenyl) methanaminium chloride (4MPMAC) has been synthesized by the low-temperature solvent evaporation method. Single crystal X-ray diffraction (SCXRD) analysis reveals the monoclinic crystal system with centrosymmetric space group, P21/c. Powder X-ray diffraction (PXRD) study justifies the structure and crystalline perfection of 4MPMAC crystal. Protonation, hydrogen bond interaction and the molecular structure of the grown crystal are confirmed by Fourier transform infrared (FT-IR) and Nuclear magnetic resonance (NMR) spectral analysis. Thermogravimetric (TG) and differential thermal analysis (DTA) elucidate the thermal stability and the melting point (222 °C) of the crystal. 4MPMAC shows the soft mechanical nature with the realization of reverse indentation size effect. UV-vis-NIR analysis reveals the wide window of optical transmission from 299 nm to 1100 nm. The bandgap of the crystal is found to be 4.16 eV. Z-scan study explores the higher third-order susceptibility and confirms the self-defocusing and saturable absorption nature of 4MPMAC crystal. The intermolecular hydrogen bonding improves the transfer of protons between the cation and anion and enhances the third-order optical nonlinearity for photonic applications. Further, the optical power limiting property is also assessed, the threshold limiting value is determined to be 24.3 mV and enables the crystal for optical limiting applications.