Synthesis, spectral, thermal, optical, electrical, mechanical and structural characterisations and quantum chemical study of 4-nitrophenol: Urea molecular adduct crystals

Organic non-linear single crystals of 4-Nitrophenol: Urea Adduct (NPUA) have been grown by slow evaporation-solution growth technique. The elemental analysis of the compound satisfies the stoichiometric expectations. Vibrational frequencies of the grown crystals have been identified by using FT-IR analysis. The presence of different protons and carbon atoms of the grown adduct was ascertained by 1H and 13C NMR analyses. The UV–Visible spectroscopy study revealed that the grown crystal has excellent transmittance and has wide band gap in the visible province. The fluorescence emission spectrum has also been recorded. Photoconductivity studies confirm positive photoconductivity nature of the crystals. The crystal belongs to the triclinic system with space group P1. The complete structural analysis of the grown crystal has been done using single crystal X-ray diffraction technique. Thermogravimetry (TG), Differential Thermal Analysis (DTA) and Differential Scanning Calorimetry (DSC) were carried out to characterise the thermal behaviour and stability of NPUA. Dielectric studies have been carried out at room temperature. Mechanical behaviour of NPUA was studied by Vickers’s microhardness test. The nonlinear optical (NLO) activity test using a Q-switched and pulsed Nd: YAG laser confirms the generation of second harmonics. The Density Functional Theoretical (DFT) study affords further insight on the properties of the compound. Quantum Chemical Calculations (QCC) have been performed through DFT method at B3LYP/6-31G(d) level of theory. The optimised geometric parameters such as bond lengths, bond angles, dipole moment, optimisation energy and vibrational frequencies were reported and compared with the experimental data.