A density functional investigation of charge transfer and structural distortions of cuprous(I) bis-phenanthroline under photo-induced excitation

The charge transfer and structural distortions that occurred in the complexes cuprous(I) bis-phenanthroline (Cu(NN)₂⁺) (NN denotes 1,10-phenanthroline, 2,9-dimethyl-1,10-phenanthroline and 2,9-di(trifluoromethyl)-1,10-phenanthroline) upon excitation with an irradiation of light were studied by density functional theory (DFT). The calculations showed that the electrons transferred from central metal Cu to ligands with the transition of the complexes Cu(NN)₂⁺ from ground state to excited state. As a consequence, the central copper in the excited state of Cu(NN)₂⁺ exhibited similar electronic density to that in the corresponding complex Cu(NN)₂²⁺. Accompanying with this transfer process, the coordination polyhedra of Cu(NN)₂⁺ became distorted upon excitation. The structural distortion was significantly reduced by increasing the steric bulk of the 2- and 9-positions substituents in the ligands NN, which is helpful for the increase of the life time of the excited state.