Luminescent iridium(III)-terpyridine complexes - Interplay of ligand centred and charge transfer states

Electrochemical properties, ground state absorption spectra, luminescence spectra and lifetimes (at room temperature and 77 K) as well as transient absorption spectra are reported herein for newly synthesized iridium(III) complexes in which benzamide units are appended to the coordinated terpyridine fragments. The nature of the luminescent excited states (Φ < 2 × 10^-3 and τ in the microsecond range, in air-equilibrated acetonitrile at 298 K) is discussed with regards to the ligand-centred ( ³LC) or charge transfer (³CT) nature. At room temperature, the excited state, a predominantly ligand-centred triplet (³LC) for the iridium(III) terpyridine compounds, is switched for the benzamide-containing complexes to a charge transfer state (³CT). Intense absorption in the visible range, high energy content, long excited states lifetimes at 298 and 77 K and good luminescence yields make these complexes very promising as photosensitisers (P). The CT nature of the excited states of the benzamide-containing complexes makes them ideal components for the construction of rigid, linear arrays of the Donor-P-Acceptor type for charge separation.