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Luminescence and Light-Driven Energy and Electron Transfer from an Exceptionally Long-Lived Excited State of a Non-Innocent Chromium(III) Complex.

ABSTRACT: Photoactive metal complexes employing Earth-abundant metal ions are a key to sustainable photophysical and photochemical applications. We exploit the effects of an inversion center and ligand non-innocence to tune the luminescence and photochemistry of the excited state of the [CrN₆ ] chromophore [Cr(tpe)₂ ]³⁺ with close to octahedral symmetry (tpe=1,1,1-tris(pyrid-2-yl)ethane). [Cr(tpe)₂ ]³⁺ exhibits the longest luminescence lifetime (?=4500??s) reported up to date for a molecular polypyridyl chromium(III) complex together with a very high luminescence quantum yield of ?=8.2?% at room temperature in fluid solution. Furthermore, the tpe ligands in [Cr(tpe)₂ ]³⁺ are redox non-innocent, leading to reversible reductive chemistry. The excited state redox potential and lifetime of [Cr(tpe)₂ ]³⁺ surpass those of the classical photosensitizer [Ru(bpy)₃ ]²⁺ (bpy=2,2'-bipyridine) enabling energy transfer (to oxygen) and photoredox processes (with azulene and tri(n-butyl)amine).

SUBMITTER: Treiling S

PROVIDER: S-EPMC6916301 | biostudies-literature | 2019 Dec

REPOSITORIES: biostudies-literature

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Publications

Luminescence and Light-Driven Energy and Electron Transfer from an Exceptionally Long-Lived Excited State of a Non-Innocent Chromium(III) Complex.

Treiling Steffen S Wang Cui C Förster Christoph C Reichenauer Florian F Kalmbach Jens J Boden Pit P Harris Joe P JP Carrella Luca M LM Rentschler Eva E Resch-Genger Ute U Reber Christian C Seitz Michael M Gerhards Markus M Heinze Katja K

Angewandte Chemie (International ed. in English) 20191031 50

Photoactive metal complexes employing Earth-abundant metal ions are a key to sustainable photophysical and photochemical applications. We exploit the effects of an inversion center and ligand non-innocence to tune the luminescence and photochemistry of the excited state of the [CrN6 ] chromophore [Cr(tpe)2 ]3+ with close to octahedral symmetry (tpe=1,1,1-tris(pyrid-2-yl)ethane). [Cr(tpe)2 ]3+ exhibits the longest luminescence lifetime (τ=450 ...[more]

PMID: 31600421

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Project description:A series of cationic heteroleptic iridium(III) complexes bearing tris-diimine ligands [Ir(phen)2(R-phen)]3+ (R-phen = phenanthroline (1), 3,8-diphenylphenanthroline (2), 3,8-dipyrenylphenanthroline (3), 3-phenylphenanthroline (4), 3-pyrenylphenanthroline (5), and 3,8-diphenylethynylphenanthroline (6)) were synthesized and characterized. These complexes possessed phen ligand-localized 1?,?* transitions below 300 nm, and charge transfer (1CT) and/or 1?,?* transitions between 300 and 520 nm. In 1, 2, 4, and 6, the low-energy bands were mixed 1CT/1?,?*. However, the increased ?-donating ability of the pyrenyl substituent(s) in 3 and 5 split the low-energy bands into a pyrene-based 1?,?* transition at 300-380 nm and an intraligand charge transfer (1ILCT) transition at 380-520 nm. All complexes were emissive at room temperature in CH3CN, but the parentage of the emitting state varied depending on the R substituent(s). Complex 1 exhibited predominantly phen ligand-localized 3?,?* emission mixed with metal-to-ligand charge transfer (3MLCT) character, whereas the emission of 2, 4, and 6 was predominantly from the excited-state with 3?,?*/3ILCT/3MLCT character. The emission from 3 and 5 was dominated by pyrene-based 3?,?* states mixed with 3ILCT character. The different natures of the lowest triplet excited states were also reflected by the different spectral features and lifetimes of the triplet transient absorption of these complexes. Complexes 3 and 5 had singlet oxygen quantum yields as high as 81 and 72%, respectively. Both gave submicromolar phototoxicities toward cancer cells (SK-MEL-28 human melanoma) and bacteria ( S. aureus and S. mutans) with visible-light activation (and marginal to no photobiological activity with red light). Their visible-light phototherapeutic indices (PIs) toward SK-MEL-28 cells were 248 for 3 and >435 for 5; PIs were lower in bacteria (?62) because of their inherent antimicrobial activities. Both complexes were shown to produce substantial amounts of intracellular reactive oxygen species (ROS), which may account for their photobiological activities.

Dataset Information

Luminescence and Light-Driven Energy and Electron Transfer from an Exceptionally Long-Lived Excited State of a Non-Innocent Chromium(III) Complex.

Publications

Luminescence and Light-Driven Energy and Electron Transfer from an Exceptionally Long-Lived Excited State of a Non-Innocent Chromium(III) Complex.

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