Multicolor emitting from a single component emitter: New iridium(III) complexes with ancillary ligand 2-(2-hydroxyphenyl) benzothiazole

Four new types of Ir(III) complexes (ppy)2Ir(LX) (ppy = 2-phenylpyridine, LX = BTZ, 3-MeBTZ, 4-MeBTZ, and 4-TfmBTZ) were synthesized and investigated by optical spectroscopy, electrochemistry as well as density functional theory (DFT). These complexes all exhibit multi-emission bands under ultraviolet light excitation at room temperature because there are efficient energy transfers between different excited states (1LC, 1MLCT, 1ILCT, 3MLCT, 3ILCT), especially for complexes I–III. The blue emitting relates to the fluorescence of Ir(R-BTZ) and the green emission originates in 3MLCT emission of Ir(ppy)2 fragment. The red emission corresponds to 3ILCT transition (R-BTZ → ppy) for complexes I–III, but 3MLCT transition of Ir(4-TfmBTZ)2 fragment for (ppy)2Ir(4-TfmBTZ). The red emission peak wavelength can be fine-tuned from 583 to 626 nm by the electron withdrawing or donating substituent at 3- or 4-position of BTZ ligand. For these single component complexes with multicolor emitting, a very promising application is the generation of white light. Although these complexes span non-uniformly the spectral range of the visible region and consequently are insufficient to produce satisfactory white light characteristics, the luminescence mechanism of them provides a new strategy for designing organic white light-emitting material.