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.

Sensitized Photochemical CO2 Reduction by Hetero‐Pacman Compounds Linking a ReI Tricarbonyl with a Porphyrin Unit

“…The UV/Vis absorption spectra of Re‐bpy and Re‐tpy in dichloromethane show a medium intensity ligand centered transition at approximately 300 nm and a weaker broad band at around 390 nm, assigned to a 1 MLCT absorption involving the diimine ligand; in agreement with the latter occurring at 401 nm ( ϵ =3600 mol −1 L cm −1 ) for Re‐bpy in CH 3 CN . By contrast, tetramesitylporphyrinato zinc ( Zn‐TMP ) shows a strong (Soret) absorption centered at 423 nm and moderately intense Q‐band absorption bands centered at 547 nm in CH 2 Cl 2 .…”

Intramolecular triplet–triplet energy transfer enhanced triplet–triplet annihilation upconversion with a short-lived triplet state platinum(ii) terpyridyl acetylide photosensitizer

“…A coumarin-containing cyclometalated iridium(III) complex with a long-lived ligand-localized triplet excited state ( 3 IL state, τ = 75.5 μs) was reported by Zhao's group 13 , and an upconversion quantum yield of 21.3% was obtained in a TTA-UC system using this complex as the photosensitizer. Similar design has been adopted in their series works [14][15][16] and enhanced upconversion performance was observed. Similar design has been adopted in their series works [14][15][16] and enhanced upconversion performance was observed.…”

Deep Red to Near‐Infrared Emitting Rhenium(I) Complexes: Synthesis, Characterization, Electrochemistry, Photophysics, and Electroluminescence Studies

“…Keywords: charge transfer · luminescence · near-infrared · organic light-emitting diodes · rhenium ied the luminescence properties of [ClRe(CO) 3 A C H T U N G T R E N N U N G (N^N)] (N^N = 1,10-phenanthroline and derivatives) and discovered an intense photoluminescence that has been ascribed to the 3 MLCT [dp(Re)-p*A C H T U N G T R E N N U N G (N^N)] excited state origin. [11] Later, rhenium(I) complexes have been widely investigated in many areas such as in Langmuir-Blodgett films, [12] photochromic materials, [13] metallogels, [14] chemosensing, [15] photosensitizers, [16] molecular dyads and triads, [17] photocatalysis, [18] biolabeling, [19] probes for proteins, [20] and OLED materials. [21] In particular, rhenium(I) metal complexes are superior luminescent materials, which demonstrate high luminescence quantum yields at room temperature, as well as high thermal and chemical stabilities.…”