Development and Physicochemical Investigation of a p-Anisidine-3,5-Dinitrobenzoic Acid Crystalline Material

A novel crystalline material based on p-anisidine and 3,5-dinitrobenzoic acid (ADNBA) was synthesized using a slow evaporation solution growth technique. Single-crystal X-ray diffraction (SCXRD) confirmed a monoclinic crystal system with the P2₁/c space group. Spectroscopic characterization through FTIR, ¹H-NMR, ¹³C-NMR, and UV-Vis analyses confirmed the formation of a charge-transfer complex, with hydrogen bonding interactions playing a crucial role in molecular stabilization. Thermal analysis (TG-DTA) indicated phase purity and stability up to 70.2°C, with decomposition occurring beyond 228°C. Microhardness testing revealed a soft material with a Meyer’s index of 2.78, and additional tests at higher loads (>100 g) confirmed plastic deformation. Dielectric studies showed a decrease in dielectric constant with increasing frequency, enhancing its suitability for nonlinear optical applications. Density Functional Theory (DFT) calculations using the B3LYP/6-311++G(d,p) method revealed a HOMO-LUMO energy gap of 0.01915 eV, which was compared with the 2.92 eV experimental band gap from Tauc’s plot. Nonlinear optical (NLO) properties were confirmed through hyperpolarizability analysis and Z-scan experiments, demonstrating positive nonlinear refraction and two-photon absorption behavior. Antibacterial studies indicated potent activity against Staphylococcus aureus, Bacillus subtilis, Klebsiella pneumoniae, and Pseudomonas aeruginosa, while antifungal tests showed inhibition against Candida albicans, Aspergillus niger, and Aspergillus fumigatus. Mechanistic insights suggested that reactive oxygen species (ROS) generation contributes to the antimicrobial effect. Preliminary cytotoxicity tests on human fibroblast cells showed an IC₅₀ of 250 μg/mL, indicating moderate biocompatibility. The ADNBA complex also demonstrated strong antioxidant potential against DPPH radicals. These findings highlight ADNBA as a promising multifunctional material for nonlinear optical and biomedical applications.