Quantum chemical study of the electronic properties of an Iridium-based photosensitizer bound to medium-sized silver clusters

The equilibrium structures and electronic excitation spectra of the Ir(III) photosensitizer Ir(ppy)$_2$(bpy)]$^+$ bound to medium-sized silver clusters Ag$_n$ ($n=$19, 20) are investigated using time-dependent density functional theory. The long-range corrected LC-BLYP approach is used with a system-specific range separation parameter. The weak physisorption of the hybrid complexes yield only small changes in the broadened absorption spectra of the hybrid system as compared with its constituents. However, the density of states as well as the fine structure of the spectra is strongly modified upon complexation. It is shown that the standard range separation parameter (0.47 bohr$^{-1}$) cannot predict these properties correctly and the optimized value of 0.16 bohr$^{-1}$ should be used instead.