Growth, Structural, Spectral, and Third-Order Nonlinear Optical Analysis of Cytosinium Cytosine Para-Aminobenzoate Hydrate Crystal

Crystals of cytosinium cytosine para-aminobenzoate hydrate (CPABA) have been developed by a slow evaporation method. A single-crystal x-ray diffraction (SCXRD) technique has been carried out and it determined CPABA associates in monoclinic with the P2₁/n space group. Powder x-ray diffraction (PXRD) analysis revealed the appearance of sharp peaks in the pattern and ensured the crystalline perfection of CPABA. The transmitting ability of CPABA was examined by the UV-Vis-NIR spectral method. The obtained low-value Urbach energy (E_U) revealed the presence of fewer structural defects in the CPABA. The functional groups have been interpreted by Fourier-transform infrared (FT-IR) and FT-FT-Raman spectral techniques. The shift in the peak for C=O stretching vibration ensures the protonation of N3 site in the CPABA. The environment of proton and carbon in the CPABA has been examined by nuclear magnetic resonance (NMR) spectral methods. The protonation of cytosinium at the N3 position was established through the deviation observed in the chemical shifts of adjacent carbon atoms. The upfield shift noticed for COO⁻ ion confirms the formation of CPABA molecules. Photoluminescence (PL) spectroscopy manifested ultraviolet fluorescence emissions. The peak around the violet region indicates shallow defects, proving that CPABA has less structural disorder. Third-order nonlinear optical (NLO) properties have been estimated employing the Z-scan method. Third-order susceptibility (χ³) is found to be 1.0053 × 10⁻⁷ esu. The high χ³ value is due to the existence of N-H…O, O-H…O and N-H…N bonds present in CPABA which enhances the molecular polarization in the crystal.