Structural, topological, optical, energetic, and magnetic properties and reactivity parameters of benzidine, its radical cation, and its dication as well as molecular complexes of the benzicline dication with the F-, Cl-, Br-, I-, NO3-, HSO4-, and H2PO4- anions were calculated at the B3LYP/6-311++G(2d,2p) level of theory in the CH2Cl2 medium. The CAM-B3LYP functional (as the most reliable one) and the 6-311++G(3df,3pd) basis set were used for the UV-vis absorption spectra prediction. The obtained spectral results are in a good agreement with available experimental data. A number of the calculated global and local molecular properties, including several recently developed ones, (in general, more than 20 parameters), namely, lambda(max), the bond lengths and orders (l and L-A,L-B), adiabatic ionization energy (IEad), global electrophilicity index (omega), condensed electrophilic Fukui functions (f(+)) and dual descriptor (Delta f(A)), van der Waals molecular volume, nuclear independent chemical shifts (NICS) and QTAIM topological parameters were estimated in the critical points of the C(1)-C(1'), C(2)-C(3), and C(4)-N bonds as well as at the ring critical point. These quantities were found to be in a strong linear dependence (R-2 > 0.99 in most cases) with the number of detached electrons (N-el) from the benzidine molecule up to formation of the dication (N-el = 2). On one hand, a position of the long-wave absorption band (lambda(CT)) corresponding to the anion-to-cation charge transfer in the neutral complexes of the benzidine dication with anions, correlates with the Mulliken electronegativity of the anion (R-2 = 0.8646) and its adiabatic ionization energy (R-2 = 0.8054). On the other hand, the correlations with the anion charge in the complexes and the anion isotropic polarizability are rather poor (R-2 = 0.6392 and 0.3470, respectively). On the ground of the obtained strong relationships, one may recommend the calculated molecular properties as potentially preferable descriptors for the benzidine-based compounds in terms of the QSAR methodology.