Hydrogen-bonded structure and optical nonlinearities in the proton-transfer complex of 8-hydroxy-5-nitroquinoline with ρ-toluenesulfonic acid

Single crystals of 8-hydroxy-5-nitroquinolinium p -toluene sulfonate (HNT) were grown by the slow evaporation solution growth technique. The structure was elucidated by single crystal X-ray diffraction analysis and the crystal belongs to the monoclinic system with the space group C2/ c . The crystallinity of HNT was studied by powder X-ray diffraction analysis. The presence of functional groups was determined by FT-IR spectral analysis. The band gap energy is estimated by the application of the Kubelka–Munk algorithm. The charge transfer characteristic of the compound was studied by frontier molecular orbitals (FMOs) analysis. The first-order hyperpolarizability of the HNT molecule was found to be 285.45 × 10 − 30 esu, which is ~ 750 times higher compared to the reference urea molecule. Investigation of the intermolecular interactions and crystal studies packing via Hirshfeld surface analysis, based on single-crystal XRD, reveals that the close contacts are associated with molecular interactions. Fingerprint plots of the Hirshfeld surfaces were used to locate and analyze the percentage of hydrogen-bonding interactions. The Mulliken charge of the present molecule was theoretically analyzed. The Kurtz-Perry powder technique has been used to estimate the second harmonic generation. Observed small SHG and large hyperpolarizability are rationalized.