Structural and optical properties of salicyl-N-methyl-4-stilbazolium tosylate: Thermal, DFT, MEP and Hirshfeld surface analysis

Abstract

The structural characteristics and optimized geometry of salicyl-N-methyl-4-stilbazolium tosylate (SMST), a derivative of the prominent electro-nonlinear optic crystal 4-(N,N-dimethylamino)-N-methyl-4-toluene sulfonate (DAST) is investigated. Its morphology, spectral, vibrational, thermal, and electronic features have been examined in studies like FT-IR, UV-Transmittance spectroscopy, single crystal XRD and TG-DTA analysis. Thermal parameters like activation energy, entropy, enthalpy, and Gibbs free energy suggest that the reaction is slower and non-spontaneous. The optical constants like energy band gap, absorption coefficient, extinction coefficient, refractive index, and skin depth of SMST have been calculated. The energy band gap value is found to be 2.69 eV, which makes SMST a potential and promising material for non-linear optical applications. The dielectric behavior of SMST is in agreement with the property needed for NLO materials. Theoretical calculations like density functional theory and frontier molecular orbitals- HOMO and LUMO are investigated to analyze the structural properties, atomic arrangement, oriented geometry, and dipole moment. Molecular electrostatic potential (MEP), Hirshfeld surface, and 2D fingerprint plot analysis are examined to provide information about the molecular interaction, crystal packing, electron density, and intermolecular properties of atomic contacts. Second Harmonic Generation of SMST shows greater efficiency than urea, which confirms that SMST crystal can leads to many applications in the optical field.