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

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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.