title: Synthetic control over photoinduced electron transfer in phosphorescence zinc sensors.
abstract: Despite the promising photofunctionalities, phosphorescent probes have been examined only to a limited extent, and the molecular features that provide convenient handles for controlling the phosphorescence response have yet to be identified. We synthesized a series of phosphorescence zinc sensors based on a cyclometalated heteroleptic Ir(III) complex. The sensor construct includes two anionic cyclometalating ligands and a neutral diimine ligand that tethers a di(2-picolyl)amine (DPA) zinc receptor. A series of cyclometalating ligands with a range of electron densities and band gap energies were used to create phosphorescence sensors. The sensor series was characterized by variable-temperature steady-state and transient photoluminescence spectroscopy studies, electrochemical measurements, and quantum chemical calculations based on time-dependent density functional theory. The studies demonstrated that the suppression of nonradiative photoinduced electron transfer (PeT) from DPA to the photoexcited Ir(IV) species provided the underlying mechanism that governed the phosphorescent response to zinc ions. Importantly, the Coulombic barrier, which was located on either the cyclometalating ligand or the diimine ligand, negligibly influenced the PeT process. Phosphorescence modulation by PeT strictly obeyed the Rehm-Weller principle, and the process occurred in the Marcus-normal region. These findings provide important guidelines for improving sensing performance; an efficient phosphorescence sensor should include a cyclometalating ligand with a wide band gap energy and a deep oxidation potential. Finally, the actions of the sensor were demonstrated by visualizing the intracellular zinc ion distribution in HeLa cells using a confocal laser scanning microscope and a photoluminescence lifetime imaging microscope.
authors: Department of Bioinspired Science, Ewha Womans University, Daehyun-dong, Seodaemun-gu, Seoul 120-750, Korea.
authors: Hana
authors: H
authors: Woo
authors: Somin
authors: S
authors: Cho
authors: Yejee
authors: Y
authors: Han
authors: Weon-Sik
authors: WS
authors: Chae
authors: Dae-Ro
authors: DR
authors: Ahn
authors: Youngmin
authors: Y
authors: You
authors: Wonwoo
authors: W
authors: Nam
mesh_terms: D000588:Amines / Q000138:chemical synthesis / Q000737:chemistry*; D056831:Coordination Complexes / Q000138:chemical synthesis / Q000737:chemistry*; D004579:Electron Transport; D006367:HeLa Cells; D006801:Humans; D007495:Iridium / Q000737:chemistry*; D008024:Ligands; D049408:Luminescent Agents / Q000138:chemical synthesis / Q000737:chemistry*; D008163:Luminescent Measurements; D018613:Microscopy, Confocal; D010848:Picolinic Acids / Q000138:chemical synthesis / Q000737:chemistry*; D015032:Zinc / Q000032:analysis*
chemical_list: C501847:2,2'-dipicolylamine; D000588:Amines; D056831:Coordination Complexes; D008024:Ligands; D049408:Luminescent Agents; D010848:Picolinic Acids; D007495:Iridium; D015032:Zinc