Aldehyde bearing bis-cyclometalated Ir(III) complex as selective photoluminescence turn-on probe for imaging intracellular homocysteine

A new photoluminescence (PL) turn-on probe based on aldehyde bearing bis-cyclometalated Ir(III) complex, [Ir(bt)(2)phen-CHO](+)PF6(-) (1), is synthesized and applied to imaging homocysteine (Hcy) in living cells. The probe 1 is readily prepared by using 2-phenylbenzothiazole (bt) as main ligand and 1,10-phenanthroline-5-carboxaldehyde (phen-CHO) as ancillary ligand. Probe 1 displayed excellent selective PL enhancement in response to Hcy in neutral buffer solution based on aldehyde group cyclization reaction. The increased PL intensity of probe 1 is directly proportional to the concentration of Hcy in the range of 10 mu M to 500 mu M with a detection limit of 4.6 mu M. More importantly, probe 1 can highly discriminate Hcy from cysteine (Cys), which is agreed with the higher luminescent quantum yield of the adduct of probe 1 and Hcy (1-Hcy, 0.46) compared with that of probe 1 and Cys (1-Cys, 0.05) in 10 mM phosphate buffer solution (pH 7.4). Furthermore, the probe I has appreciable cell permeability and low cytotoxicity and has been successfully applied to selectively imaging Hcy in living cells. The superior properties of the probe 1 make it of great potential use for studying the effects of Hcy in other biosystems. (C) 2017 Elsevier B.V. All rights reserved.