Hydrogen bond analysis of a third order nonlinear optical crystal, 2-amino-5-bromopyridinium benzilate, using structural and computational characterizations

Abstract

The molecular structure of a proton transfer organic material, 2-amino-5-bromopyridinium benzilate crystal, grown by slow-evaporation solution growth technique has been determined by single crystal X-ray diffraction. The crystal has monoclinic structure and crystallizes in a centrosymmetric space group P21/c. The molecular network contains variety of hydrogen bonds that led to stabilization of the structure and optical properties of the crystal. The FT-IR studies confirm the functional groups present. The 1H and 13C NMR spectra were recorded to confirm the molecular skeleton. The crystal is transparent in entire visible region as evidenced by UV–vis spectrum. The photoluminescence spectrum of the compound shows good optical emission properties. Thermal stability of the crystal was determined using TG/DTA studies. Theoretically optimized molecular geometry shows good agreement with experimental bond length and bond angle values. Molecular electrostatic potential analysis confirmed the proton migration during the reaction. The charge transfer occurring in the compound was confirmed by both HOMO-LUMO and Mulliken atomic charge analysis, where electrons get promoted from pyridinium moiety to the benzilate through N–H⋯O hydrogen bonds. Natural bond orbital analysis supports the interactions and structural properties of the proton transfer compound. Z-scan technique was used to measure the effective third-order nonlinear optical susceptibility.