Growth, structural, optical, thermal, laser damage threshold and theoretical investigations of organic nonlinear optical 2-aminopyridinium 4-nitrophenolate 4-nitrophenol (2AP4N) single crystal

The good quality organic 2-aminopyridinium 4-nitrophenolate 4-nitrophenol (2AP4N) single crystals with the dimension of 30 × 5 × 5 mm³ have been grown by slow evaporation solution technique (SEST) at ambient temperature within the period of 30 days using methanol as solvent. Initially, the structure of grown 2AP4N single crystal was confirmed by the single crystal X-ray diffraction (SXRD). Intermolecular interactions of 2AP4N molecule were analyzed by Hirshfeld surface analysis. The grown crystal was studied by powder X-ray diffraction (PXRD) measurement, it has sharp peaks which indicates good crystallinity. The presence of various functional groups have been confirmed by FTIR and FT-Raman spectra analysis. The optical quality (transparency) of the grown crystal was studied by UV–Vis NIR spectral analysis and it has good optical transparency in the visible and near IR regions with the cut-off wavelength of 470 nm. The energy values of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) have been calculated. The density of states (DOS) spectra was used to study the bonding, anti-bonding and non-bonding interactions. The Mulliken charge distribution was used to confirm the sign and magnitude of charge of each atom. The distribution of charge and its related properties were analyzed by the molecular electrostatic potential (MEP). The natural bonding orbital (NBO) theory was used to analyse the inter-intra molecular interactions of 2AP4N. First-order hyperpolarizability (β_total) of 2AP4N molecule was found to be 1.071⁻²⁹ esu, which is 28.6 times that of urea. Photoluminescence measurement reveals that the 2AP4N crystal has very high emission at 500 nm. The thermal stability of grown crystal was found to be 90 °C. The dislocation density was analyzed and it was confirmed to possess less defects. The laser damage threshold (LDT) energy has been measured by using Nd: YAG laser (532 nm). The efficiency of second harmonic generation (SHG) of grown 2AP4N was evaluated by Kurtz-Perry powder technique. The SHG efficiency of 2AP4N was found to be 4.5 times that of standard KDP material. The high SHG values of 2AP4N crystals may be more favorable for nonlinear optical (NLO) device applications.