Deep-red or near-infrared-emitting Iridium (III) complex as efficient phosphorescent dye for live cell imaging through staining in cytoplasm

Abstract

Despite the bioimaging highly realized from Ir(III)-complexes with visible-light, the staining on organelles by NIR-emissive (NIR = near infrared) Ir(III)-complex species especially in cytoplasm was rarely reported. In this work, two new cationic iridium (III) complexes ({[Ir(C^N)₂(N^N)]⁺ ·(PF₆)⁻}; C^N = 2,3-diphenylquinoxaline (dpqx)⁻ or 1-(benzo[b]-thiophen-2-yl)-isoquinoline (iqbt)⁻; N^N = 2-(pyridin-2-yl)-5-(4-vinylphenyl)pyridine (4vp-2,2′-bpy)), namely {[Ir(dpqx)₂(4vp-2,2′-bpy)]⁺ ·(PF₆)⁻} (1) and {[Ir(iqbt)₂(4vp-2,2′-bpy)]⁺ ·(PF₆)⁻} (2) with efficient deep-red (${\lambda }_{\text{em}}^{\text{Max}}$ = 630 nm, Φ_PL = 0.19) and NIR-emissions (${\lambda }_{\text{em}}^{\text{Max}}$ = 683 nm, Φ_PL = 0.16), are obtained, respectively. Moreover, beneficial from the excellent biocompatibility and low cytotoxicity, each of the two cationic iridium (III) complexes 1 and 2, enables to exclusively stain in the cytoplasm of live cells. This research might provide two ideal candidates in the design of high-efficiency deep-red or NIR emitting cationic iridium (III) complexes for specific bioimaging agents.