Crystal structure, spectral, thermal, optical, laser damage, NLO study and quantum chemical calculations of a noncentrosymmetric crystal N, N′-diphenylguanidinium p-toluenesulphonate

Abstract

A novel NLO active crystal diphenylguanidinium p-toluenesulphonate (DPGPTS) single crystals were grown successfully by slow-evaporation solution growth technique and the structure was confirmed by single crystal X-ray diffraction technique. The crystal was subjected to FT-IR and NMR spectroscopic techniques in order to elucidate functional group and the arrangement of carbons and hydrogens. High transparency (70%) and low energy band gap of 4.25 eV in DPGPTS was confirmed through UV-NIR study. The Laser damage threshold of DPGPTS was measured using Nd:YAG (λ = 1064 nm) laser. Thermal stability of the crystal was studied through TG/DTA thermogram. Green, violet and ultra violet emission properties were analysed by photoluminescence. Low HOMO-LUMO energy gap of 4.75 eV measured in theoretical calculations proves the eventual charge transfer taking place within the system. Frontier Molecular Orbital analysis clearly depicts the occurrence of intermolecular NH⋯O hydrogen bond influencing the charge transfer in the system. Optimized geometry also proves that the hydrogen bonding interaction's role in the electronic charge transfer between cationic and anionic moiety. The presence of various hyperconjugative interactions were evaluated through Natural Bond Orbital analysis. Molecular Electrostatic Potential study predicts the possible sites for hydrogen bonding nucleophilic and electrophilic interactions. Mulliken charge analysis demonstrates the accumulation of positive and negative charge on atoms and their participation in hydrogen bonding interactions. The calculated first order hyperpolarizability is found to be 6.25 times than that of urea.