Unusually Fast Phosphorescence from Ir(III) Complexes via Dinuclear Molecular Design.

The design and detailed photophysical study of two novel Ir(III) complexes featuring mono- and dinuclear design are presented. Emission quantum yield and decay times in solution are Φ = 90% and τ(300 K) = 1.16 μs for the mononuclear complex , and Φ = 95% and τ(300 K) = 0.44 μs for the dinuclear complex . These data indicate an almost 3-fold increase in the phosphorescence rate for dinuclear complex compared to . Zero-field splitting (ZFS) of the T state also increases from ZFS = 65 cm for the mononuclear complex to ZFS = 205 cm for the dinuclear complex and is accompanied by a drastic shortening of the individual decay times of T substates. With the help of TD-DFT calculations, we rationalize that the drastic changes in the T state properties in the dinuclear complex originate from an increased number of excited states available for direct spin-orbit coupling (SOC) routes as a result of electronic coupling of Ir-Cl antibonding molecular orbitals of the two coordination sites.