Tunable dual‐emission from cyclometallated Ir(III) Complexes carrying emissive aryl‐isocyanide ancillary ligands

The ability to control the excited-state properties of luminescent transition metal complexes is essential for sensing applications, optoelectronics and artificial photosynthesis. Luminescent cyclometalated iridium(III) complexes have been shown to be excellent candidates in these fields because of their superior photophysical properties such as high quantum efficiency and short excited state lifetimes. The emission color of these complexes is typically determined by the ligand with the lowest triplet energy. In this presentation we report a family of iridium(III) complexes of formula (ppy)2Ir(CN-R)(X) (R= t-Butyl; 1-naphtyl; 2-naphtyl. X= CN, Cl) with strategically matched ligands that have closely spaced triplet energies. The complexes undergo intramolecular excitation transfer between both the cyclometallated 3MLCT (ppy-based) state and the long-lived, lower energy 3-* state of the ancillary CN-R (Rt-Bu). For example, compound 1 (R= 2-naphtyl; X= CN) emits at room temperature in fluid solution (=0.15; =0.7ms) from both the 3MLCT state (max.=452nm) and the 3-* state of 2-isocyano-naphtalene (max=488nm). The emission profile of 1 is unchanged when doped in a PMMA film, however, the efficiency increases 5-fold (=0.83; =2.5ms) due to strong suppression of the non-radiative decay rates. In conclusion, this luminescent (ppy)2Ir(CN-R)(X) complexes display efficient dual-emission due to energy shuttling between the different chromophores.