Growth, spectral and quantum chemical investigation on hexamethylenetetramine 4-nitrophenol monohydrate single crystals for second harmonic generation and optical limiting applications

Abstract

To grow single crystals of hexamethylenetetramine 4-nitrophenol monohydrate (HMTNP), the solvent evaporation method was used. The single crystal X-ray diffraction (SCXRD) method is used to confirm the crystal lattice parameters and space group. Powder X-ray diffraction, 1H, and 13C NMR, FTIR, and FT-Raman spectroscopy were employed to investigate the title crystal's crystalline nature, molecular arrangement, and presence of functional groups. The Hirshfeld surface study is aimed at investigating the intermolecular charge-transfer interactions that occur in HMTNP owing to the presence of OH···N, CH···O, and OH···O hydrogen bonds. UV-Visible and photoluminescence studies were used to determine the lower cut-off wavelength and emission peaks. Additionally, the title crystal's optical band gap energy has been estimated to be 3.17 nm. Dielectric and photoconductivity investigations of the single crystal revealed dielectric constant values and a negative photoconductivity response. The Second Harmonic Generation (SHG) efficiency of the powder crystal is 4.31 times that of a conventional KDP crystal. In Z-scan and optical limiting experiments, the self-defocusing nature and optical limiting behavior of HMTNP were demonstrated. Furthermore, DFT calculations at the B3LYP/6–311++G(d,p) level of theory were utilized to investigate the formed crystal's molecular structural geometry, molecular vibration, intermolecular charge transfer interactions and hyperpolarizability.