Nonlocal hybrid density functional theory method is used to study the structure and force field of the copper(I)-diphenanthroline cation. It is demonstrated that it possesses D-2d symmetry in the S-0 state, however, deformations to D-2 symmetry with rotated phenanthroline rings are not costly energetically and, in fact, such D-2 structure is the minimum of the T-1 state. Time-dependent DFT method is utilized to calculate the excited electronic states and the visible and UV absorption spectrum. It is shown that the S-3 state of B-2 symmetry and of metal-to-ligand charge transfer (MLCT) character, is responsible for the ca. 470 nm visible absorption band, while dipole transitions to the S-1 and S-2 states are symmetry forbidden. We find four triplet electronic states closely spaced and lying just below the S-1 state. The ordering and spacing of the lowest triplet and singlet excited states nicely explains the properties of the observed photoluminescence. The calculated maximum of photoluminescence of 759 nm is in a good agreement with the experiment (ca. 730 nm). (C) 2003 American Institute of Physics.