A series of 2‐phenylbenzothiazole‐based iridium complexes with N‐H derivatives: synthesis, photophysics, DFT calculations and a preliminary exploration in fluoride ions sensing

Abstract

A series of new pbt‐based Ir(III) complexes containing N−H derivatives ancillary ligands (piz/pbiz) were designed and synthesized rationally, naming [(CH3Opbt)2Ir(piz)][PF6] (Ir1), [(CF3pbt)2Ir(piz)][PF6] (Ir2), [(Fpbt)2Ir(piz)][PF6] (Ir3), [(CH3Opbt)2Ir(pbiz)][PF6] (Ir4), [(CF3pbt)2Ir(pbiz)][PF6] (Ir5) and [(Fpbt)2Ir(pbiz)][PF6] (Ir6) (where pbt=2‐phenylbenzothiazole, piz=2‐(1H‐imidazol‐2‐yl)pyridine, and pbiz=2‐(pyridin‐2‐yl)‐1H‐benzoimidazole). Combined with photophysical properties and theoretical calculations, their structure‐property relationships were systematically researched. These iridium(III) complexes are phosphorescent in the green and yellow‐green region with quantum yields of 14.1–28.7 % and lifetimes of 0.35–0.88 μs. Considering the relatively high quantum yield and imidazole group on ancillary ligands, [(CF3pbt)2Ir(pbiz)][PF6] (Ir5) was preliminary explored as the phosphorescent sensor toward F− ions. The results showed that the addition of fluoride ions to complex Ir5 in dichloromethane solution induced a red shift of the emission color, along with an enhancement in the luminescent intensity. Theoretical calculations were carried out to understand the mechanism, and the results reveal that the hydrogen bonding interaction of N−H bond with F− influence the electron transfer processes of the lowest energy absorption and emission, leading to a significant change in the photophysical properties.