Synthesis, characterization and optical properties of novel Ir(III) complexes bearing N-heterocycle substituents

A series of cationic heteroleptic Ir(III) complexes with different N-heterocycle groups (N-phenothiazinyl, N-indolyl, N-carbazolyl, 3,6-di-tert-butyl-N-carbazolyl) were synthesized and characterized. The photophysical properties of these complexes were systematically investigated. All complexes exhibit strong ¹π-π^∗ absorption bands in the UV region and broad ¹MLCT absorption bands in the visible region. In addition, these complexes exhibit weak absorption after 500 nm, which could be attributed to ³π,π^∗/³CT transition. All complexes exhibit broad and structureless emission bands from 568 nm to 627 nm at room temperature, which are originated from ³MLCT/³LLCT excited states. The electron donating substituents attached on the 2-phenylpyridine ligands cause a pronounced red-shift of the emission band. Except 1d, all complexes show strong triplet transient absorptions from UV to visible region, which were assigned to the ³MLCT/³π,π^∗ excited state. In addition, complexes 1a-1c all exhibit reverse saturable absorption (RSA) at 532 nm, which follows the trend of 1a>1b > 1c. The photophysical properties of these Ir(III) complexes can be influenced drastically by the substituents on 2-phenylpyridine ligands, which would be useful for rational design of optical functional materials.