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.

Electroluminochromic Materials and Devices Based on Metal Complexes

“…[45][46][47][48][49] Compared to neutralo nes, ionic Ir III complexesh ave unique advantages such as milder synthesis conditions and stable redox reversibility.M oreover,t hey also have varieties of charge-transfer excited states, including intraligand charget ransfer ( 3 ILCT), ligand-to-ligand charge transfer ( 3 LLCT), metal-to-ligand-ligand charge transfer ( 3 MLLCT) and triplet metal-to-ligand charge transfer ( 3 MLCT) states. [50][51][52][53][54][55] These excited states are sensitive to externale nvironment, which makes ionic Ir III complexess uitable for constructing an excellent class of electrical stimuli-responsivematerials.…”

The crystal structure of bis{3,5-difluoro-2-[4-(2,4,6-trimethylphenyl)pyridin-2-yl]phenyl}(picolinato)iridium(III) and its 4-tert-butylpyridin-2-yl analogue

“…Phosphorescent cyclometallated iridium(III) compounds have been investigated for a variety of applications, including solar cells (Kim et al, 2016), sensors (Marín-Suá rez et al, 2012), bioimaging (Zhang et al, 2015), and scintillators (Bertrand et al, 2015). However, their most widespread use stems from their electrophosphorescence and research in this area has focused on their use in organic light-emitting diodes (OLED) (Choy et al, 2014;Chi & Chou, 2010;Fu et al, 2011).…”

Construction of a crystalline 14-metal Zn–Nd rectangular nanocluster with a dual-emissive response towards metal ions

“…Recently, dualemissive probes with two emission bands have been designed to make the response more accurate by the self-calibration of the uorescence signals. [7][8][9][10][11][12][13] For example, some dual-emissive probes such as uorescent organic compounds, 14,15 nanoparticles 16,17 and d-block metal complexes 18,19 have been used for this purpose in biologic imaging.…”