Electronic structures, DNA-binding and spectral properties of Co(III) complexes [Co(bpy)2(L)]3+ (L=pip, odhip, hnoip)

Studies on the electronic structures and trend in DNA-binding affinities of a series of Co(Ш) complexes have been carried out, using the density functional theory (DFT) at the B3LYP/LanL2DZ level. The optimized geometric structures of these Co(Ш) complexes in aqueous solution are more close to experimental data than those in vacuo. The electronic structures of these Co(Ш) complexes were analyzed on the basis of their geometric structures optimized in aqueous solution, and the trend in the DNA-binding constants (Kb) was reasonably explained. In addition, the electronic absorption spectra of these complexes were calculated and simulated in aqueous solution using the time dependent DFT (TDDFT) at the B3LYP/LanL2DZ level. The calculated absorption spectra of these Co(Ш) complexes in aqueous solution are in satisfying agreement with experimental results, and the properties of experimental absorption bands have been theoretically explained in detail. Meanwhile, in order to explore the solvent effect on the absorption spectra of these Co(Ш) complexes, their absorption spectra in vacuo were also calculated, and the results show that the calculated absorption spectra of Co(Ш) complexes are greatly influenced by the solvent effect.