title: Visible light-absorbing rhenium(I) tricarbonyl complexes as triplet photosensitizers in photooxidation and triplet-triplet annihilation upconversion.
abstract: We prepared N^N Re(I) tricarbonyl chloride complexes (Re-1 and Re-2) that give very strong absorption of visible light. To this end, it is for the first time that boron dipyrimethane (Bodipy) was used to prepare Re(I) tricarbonyl chloride complexes. The π-conjugation linker between the π-conjugation framework of the antenna Bodipy and the Re(I) coordination centre ensures efficient intersystem crossing (ISC). Re-0 without visible light-harvesting ligand was prepared as a model complex in the photophysical studies. Re-1 (with Bodipy) and Re-2 (with carbazole-ethynyl Bodipy) show unprecedented strong absorption of visible light at 536 nm (ε = 91700 M(−1) cm(−1)) and 574 nm (ε = 64,600 M(−1) cm(−1)), respectively. Interestingly, different from Re-0, Re-1 and Re-2 show fluorescence of the ligand, not the phosphorescence of the Re(I) coordination centre. However, long-lived triplet excited states were observed upon visible light excitation (τ(T) = 104.0 μs for Re-1; τ(T) = 127.2 μs for Re-2) vs. the short lifetime of Re-0 (τ(T) = 26 ns). With nanosecond time-resolved transient absorption spectroscopy and DFT calculations, we proved that the triplet excited states of Re-1 and Re-2 are localized on the Bodipy ligands. The complexes were used as triplet photosensitizers for two triplet–triplet-energy-transfer (TTET) processes, i.e.(1)O(2) mediated photooxidation and triplet–triplet annihilation (TTA) upconversion. With the strong visible light-harvesting ability, Re-1 proved to be a better (1)O(2) photosensitizer than the conventional triplet photosensitizer tetraphenylporphyrin (TPP). Significant upconversion was observed with Re-1 as the triplet photosensitizer. Our result is useful for preparation of Re(I) tricarbonyl chloride complexes that show strong absorption of visible light and long-lived triplet excited states and for the application of these complexes as triplet photosensitizers in photocatalysis, photodynamic therapy and TTA upconversion.
authors.affiliation: State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, E-208 West Campus, 2 Ling-Gong Road, Dalian 116024, PR China.
authors.forename: Xiuyu
authors.initials: X
authors.lastname: Yi
authors.forename: Jianzhang
authors.initials: J
authors.lastname: Zhao
authors.forename: Jifu
authors.initials: J
authors.lastname: Sun
authors.forename: Song
authors.initials: S
authors.lastname: Guo
authors.forename: Hongli
authors.initials: H
authors.lastname: Zhang
mesh_terms: D001896:Boron Compounds / Q000737:chemistry; D056831:Coordination Complexes / Q000138:chemical synthesis / Q000737:chemistry*; D004735:Energy Transfer; D008027:Light; D010084:Oxidation-Reduction; D017319:Photosensitizing Agents; D011789:Quantum Theory; D012211:Rhenium / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet
chemical_list: C095489:4,4-difluoro-4-bora-3a,4a-diaza-s-indacene; D001896:Boron Compounds; D056831:Coordination Complexes; D017319:Photosensitizing Agents; D012211:Rhenium