Three new Schiff base compounds were synthesized via condensation of 3-R-4-amino-5-hydrazino-1,2,4-triazole with dibenzoylmethane [R = H, CH3, and CH2CH3 namely L1, L2, and L3, respectively]. The synthesized Schiff bases were characterized using melting point, CHN elemental analyses, FT-IR, and 1H-NMR. The corresponding Cu(II) Schiff base complexes were synthesized via refluxing the prepared Schiff bases with CuCl2·2H2O. The synthesized complexes have been characterized by means of different spectral tools (FT-IR, ESR, and UV–Vis spectra) in addition to elemental analysis, magnetic moment, conductivity, and thermal analysis. The synthesized copper complexes are nonelectrolytes in N,N-dimethylformamide (DMF) based on their conductance values. Using modified Bauer-Kirby method, the Schiff bases and their Cu(II) complexes have been tested for antifungal (Candida albicans and Aspergillus flavus) and antibacterial (Staphylococcus aureus and Escherichia coli) activities. Moreover, CuO nanoparticles were produced via thermal decomposition of the synthesized Cu(II) complexes at 650 °C. The produced nanoparticles were characterized using XRD, HR-TEM, FT-IR, and UV–Vis spectroscopy. The CuO nanostructures exhibited good photocatalytic activity for the degradation of methylene blue dye in the presence of hydrogen peroxide with 77.36% degradation efficiency in 360 min.