Benzothiazole derivative (L) metal complexes with copper, nickel, and zinc have been synthesized. The structures of the prepared compounds were studied using various spectroscopic techniques, including H NMR spectroscopy, magnetic measurements, thermogravimetric analysis (TGA), electronic spectroscopy, and molar conductance. These techniques were employed to examine and validate the structures of the synthesized compounds. The copper and zinc complexes exhibit octahedral geometries, while the nickel complex adopts a distorted square planar geometry. The nonlinear optical (NLO) properties, geometrical optimization, and electronic transitions were theoretically investigated using the B3LYP time-dependent density functional theory (TD-DFT) with PCM (DMF as solvent). The LANL2DZ basis set was used for the metal ions, while the 6-311G** basis set was applied to carbon, hydrogen, and heteroatoms. The electronic configurations and natural charge populations were determined and reported using natural bond orbital (NBO) analysis. Global chemical reactivity descriptors were evaluated using the relatively small energy gap between the highest occupied Molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), indicating the presence of intramolecular charge transfer (ICT) within the Zn, Cu, and Ni complexes. The complexes exhibited intriguing optical properties, as suggested by their anisotropy of polarizability (α) and first-order hyperpolarizability (β) values. Furthermore, molecular docking studies revealed effective binding of the synthesized complexes to target proteins, including NI63 (Human Coronavirus), 1HK7 (Breast Cancer Protein), 6WTT (SARS-CoV-2), and 1ACL (Alzheimer's Disease Protein).