Design, Synthesis and Photophysical Studies of Luminescent Rhodium(III) Complexes in Near-Infrared Region

A series of near-infrared (NIR)-emitting cyclometalated rhodium(III) complexes have been designed, synthesized and characterized. The NIR luminescence has been realized by rational design of strong sigma-donor cyclometalating (C boolean AND N) ligand with extended pi-conjugation structure for decreasing the energy level of intraligand (IL) state. In addition, the investigation of substituents on the benzo[g]quinoxaline moiety as the carbon-donor demonstrated that the luminescence can be further shifted to the red by the introduction of electron-donating thienyl groups. The luminescence maxima of these complexes are ranging from 763 nm to 792 nm with the luminescence quantum yield (phi(lum)) of 0.41 %-0.66 % in dichloromethane solution. This work demonstrates the first example of NIR-phosphorescent rhodium(III) complexes and provides an alternative for diversifying the development of NIR materials.