Interpretation of molecular structure and third-order nonlinear optical studies of 4-methylbenzylammonium nitrate single crystal

Abstract

4-Methylbenzylammonium nitrate (4MLBANO3) has been successfully synthesized and good-quality single crystals have been grown from aqueous solution by slow solvent evaporation solution growth technique. The grown crystals have been analysed by different characterization techniques. Single-crystal X-ray diffraction analysis reveals that the grown crystal belongs to monoclinic crystal system with space group P21/c. UV–Vis–NIR spectral analysis shows that the crystal is transparent from 231 to 1100 nm. The functional groups, protonation of NH2 and the formation of 4MLBANO3 crystal have been established from FTIR analysis. The molecular structure has also been confirmed by NMR spectroscopy. The protonation of NH2 to NH3+ group is confirmed by shifts in the carbon signals observed in 13C NMR analysis. The chemical shift of methylene group bonded with NH2 group is observed at 46.21 ppm in pure 4-methylbenzylamine (4MLBA). In 4MLBANO3 this has been shifted upfield due to adjacent protonated NH3+ and it is observed at 42.32 ppm. In 1H NMR, the NH2 chemical shift of 4MLBA is observed at 1.42 ppm which is shifted to 8.096 ppm in 4MLBANO3. This confirms the protonation of NH2. The third-order optical nonlinear susceptibility (χ3), nonlinear refractive index (n2) and absorption coefficient (β) have been calculated and the values are found to be 3.57 × 10−6 esu, 6.97 × 10−8 cm2/W and 0.06 × 10−4 cm/W, respectively. The observed third-order nonlinear susceptibility value (χ3) of 4MLBANO3 has been compared with LiKB4O7, VMST, KBe2BO3F2, MMST and KDP single crystals.