title: Dual-Emissive Cyclometalated Iridium(III) Polypyridine Complexes as Ratiometric Biological Probes and Organelle-Selective Bioimaging Reagents.
abstract: In this Article, we present a series of cyclometalated iridium(III) polypyridine complexes of the formula [Ir(N^C)2(N^N)](PF6) that showed dual emission under ambient conditions. The structures of the cyclometalating and diimine ligands were changed systematically to investigate the effects of the substituents on the dual-emission properties of the complexes. On the basis of the photophysical data, the high-energy (HE) and low-energy (LE) emission features of the complexes were assigned to triplet intraligand ((3)IL) and triplet charge-transfer ((3)CT) excited states, respectively. Time-dependent density functional theory (TD-DFT) calculations supported these assignments and indicated that the dual emission resulted from the interruption of the communication between the higher-lying (3)IL and the lower-lying (3)CT states by a triplet amine-to-ligand charge-transfer ((3)NLCT) state. Also, the avidin-binding properties of the biotin complexes were studied by emission titrations, and the results showed that the dual-emissive complexes can be utilized as ratiometric probes for avidin. Additionally, all the complexes exhibited efficient cellular uptake by live HeLa cells. The MTT and Annexin V assays confirmed that no cell death and early apoptosis occurred during the cell imaging experiments. Interestingly, laser-scanning confocal microscopy revealed that the complexes were selectively localized on the cell membrane, mitochondria, or both, depending on the nature of the substituents of the ligands. The results of this work will contribute to the future development of dual-emissive transition metal complexes as ratiometric probes and organelle-selective bioimaging reagents.
authors.forename: Kenneth Yin
authors.initials: KY
authors.lastname: Zhang
authors.affiliation: ‡Department of Biology and Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, P. R. China.
authors.forename: Hua-Wei
authors.initials: HW
authors.lastname: Liu
authors.affiliation: ‡Department of Biology and Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, P. R. China.
authors.forename: Man-Chung
authors.initials: MC
authors.lastname: Tang
authors.affiliation: ‡Department of Biology and Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, P. R. China.
authors.forename: Alex Wing-Tat
authors.initials: AW
authors.lastname: Choi
authors.affiliation: §Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, P. R. China.
authors.forename: Nianyong
authors.initials: N
authors.lastname: Zhu
authors.affiliation: ‡Department of Biology and Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, P. R. China.
authors.forename: Xi-Guang
authors.initials: XG
authors.lastname: Wei
authors.affiliation: ‡Department of Biology and Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, P. R. China.
authors.forename: Kai-Chung
authors.initials: KC
authors.lastname: Lau
authors.affiliation: ‡Department of Biology and Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, P. R. China.|∥State Key Laboratory of Millimeters Waves, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, P. R. China.
authors.forename: Kenneth Kam-Wing
authors.initials: KK
authors.lastname: Lo
mesh_terms: D016923:Cell Death; D003500:Cyclization; D005456:Fluorescent Dyes / Q000138:chemical synthesis / Q000737:chemistry*; D006367:HeLa Cells; D006801:Humans; D007495:Iridium / Q000737:chemistry; D018613:Microscopy, Confocal; D008958:Models, Molecular; D009942:Organometallic Compounds / Q000737:chemistry* / Q000493:pharmacokinetics; D011725:Pyridines / Q000737:chemistry; D011789:Quantum Theory
chemical_list: D005456:Fluorescent Dyes; D009942:Organometallic Compounds; D011725:Pyridines; D007495:Iridium