1
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Schmitz M, Bertrams MS, Sell AC, Glaser F, Kerzig C. Efficient Energy and Electron Transfer Photocatalysis with a Coulombic Dyad. J Am Chem Soc 2024. [PMID: 39227057 DOI: 10.1021/jacs.4c08551] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/05/2024]
Abstract
Photocatalysis holds great promise for changing the way value-added molecules are currently prepared. However, many photocatalytic reactions suffer from quantum yields well below 10%, hampering the transition from lab-scale reactions to large-scale or even industrial applications. Molecular dyads can be designed such that the beneficial properties of inorganic and organic chromophores are combined, resulting in milder reaction conditions and improved reaction quantum yields of photocatalytic reactions. We have developed a novel approach for obtaining the advantages of molecular dyads without the time- and resource-consuming synthesis of these tailored photocatalysts. Simply by mixing a cationic ruthenium complex with an anionic pyrene derivative in water a salt bichromophore is produced owing to electrostatic interactions. The long-lived organic triplet state is obtained by static and quantitative energy transfer from the preorganized ruthenium complex. We exploited this so-called Coulombic dyad for energy transfer catalysis with similar reactivity and even higher photostability compared to a molecular dyad and reference photosensitizers in several photooxygenations. In addition, it was shown that this system can also be used to maximize the quantum yield of photoredox reactions. This is due to an intrinsically higher cage escape quantum yield after photoinduced electron transfer for purely organic compounds compared to heavy atom-containing molecules. The combination of laboratory-scale as well as mechanistic irradiation experiments with detailed spectroscopic investigations provided deep mechanistic insights into this easy-to-use photocatalyst class.
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Affiliation(s)
- Matthias Schmitz
- Department of Chemistry, Johannes Gutenberg University Mainz, Duesbergweg 10-14, 55128 Mainz, Germany
| | - Maria-Sophie Bertrams
- Department of Chemistry, Johannes Gutenberg University Mainz, Duesbergweg 10-14, 55128 Mainz, Germany
| | - Arne C Sell
- Department of Chemistry, Johannes Gutenberg University Mainz, Duesbergweg 10-14, 55128 Mainz, Germany
| | - Felix Glaser
- Department of Chemistry, Johannes Gutenberg University Mainz, Duesbergweg 10-14, 55128 Mainz, Germany
| | - Christoph Kerzig
- Department of Chemistry, Johannes Gutenberg University Mainz, Duesbergweg 10-14, 55128 Mainz, Germany
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2
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DiLuzio S, Baumer M, Guzman R, Kagalwala H, Lopato E, Talledo S, Kangas J, Bernhard S. Exploring the Photophysics and Photocatalytic Activity of Heteroleptic Rh(III) Transition-Metal Complexes Using High-Throughput Experimentation. Inorg Chem 2024; 63:14267-14277. [PMID: 39031763 PMCID: PMC11304382 DOI: 10.1021/acs.inorgchem.4c02420] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2024] [Revised: 07/08/2024] [Accepted: 07/11/2024] [Indexed: 07/22/2024]
Abstract
High-throughput synthesis and screening (HTSS) methods were used to investigate the photophysical properties of 576 heteroleptic Rh(III) transition-metal complexes through measurement of the UV-visible absorption spectra, deaerated excited-state lifetime, and phosphorescent emission spectra. While 4d transition-metal photophysics are often highly influenced by deleterious metal-centered deactivation channels, the HTSS of structurally diverse cyclometalating and ancillary ligands attached to the metal center facilitated the discovery of photoactive complexes exhibiting long-lived charge-transfer phosphorescence (0.15-0.95 μs) spanning a substantial portion of the visible region (546-620 nm) at room temperature. Further photophysical and electrochemical investigations were then carried out on select complexes with favorable photophysics to understand the underlying features controlling these superior properties. Heteroleptic Ir(III) complexes with identical ligand morphology were also synthesized to compare these features to this family of well understood chromophores. A number of these Rh(III) complexes contained the requisite properties for photocatalytic activity and were consequently tested as photocatalysts (PCs) in a water reduction system using a Pd water reduction cocatalyst. Under certain conditions, the activity of the Rh(III) PC actually surpassed that of the Ir(III) PC, uncovering the potential of this often-overlooked class of transition metals as both efficient photoactive chromophores and PCs.
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Affiliation(s)
- Stephen DiLuzio
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
| | - Mitchell Baumer
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
| | - Rafael Guzman
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
| | - Husain Kagalwala
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
| | - Eric Lopato
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
| | - Savannah Talledo
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
| | - Joshua Kangas
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
| | - Stefan Bernhard
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
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3
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Goodwin MJ, Dickenson JC, Ripak A, Deetz AM, McCarthy JS, Meyer GJ, Troian-Gautier L. Factors that Impact Photochemical Cage Escape Yields. Chem Rev 2024; 124:7379-7464. [PMID: 38743869 DOI: 10.1021/acs.chemrev.3c00930] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/16/2024]
Abstract
The utilization of visible light to mediate chemical reactions in fluid solutions has applications that range from solar fuel production to medicine and organic synthesis. These reactions are typically initiated by electron transfer between a photoexcited dye molecule (a photosensitizer) and a redox-active quencher to yield radical pairs that are intimately associated within a solvent cage. Many of these radicals undergo rapid thermodynamically favored "geminate" recombination and do not diffuse out of the solvent cage that surrounds them. Those that do escape the cage are useful reagents that may undergo subsequent reactions important to the above-mentioned applications. The cage escape process and the factors that determine the yields remain poorly understood despite decades of research motivated by their practical and fundamental importance. Herein, state-of-the-art research on light-induced electron transfer and cage escape that has appeared since the seminal 1972 review by J. P. Lorand entitled "The Cage Effect" is reviewed. This review also provides some background for those new to the field and discusses the cage escape process of both homolytic bond photodissociation and bimolecular light induced electron transfer reactions. The review concludes with some key goals and directions for future research that promise to elevate this very vibrant field to even greater heights.
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Affiliation(s)
- Matthew J Goodwin
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States
| | - John C Dickenson
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States
| | - Alexia Ripak
- Université catholique de Louvain (UCLouvain), Institut de la Matière Condensée et des Nanosciences (IMCN), Molecular Chemistry, Materials and Catalysis (MOST), Place Louis Pasteur 1, bte L4.01.02, 1348 Louvain-la-Neuve, Belgium
| | - Alexander M Deetz
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States
| | - Jackson S McCarthy
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States
| | - Gerald J Meyer
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States
| | - Ludovic Troian-Gautier
- Université catholique de Louvain (UCLouvain), Institut de la Matière Condensée et des Nanosciences (IMCN), Molecular Chemistry, Materials and Catalysis (MOST), Place Louis Pasteur 1, bte L4.01.02, 1348 Louvain-la-Neuve, Belgium
- Wel Research Institute, Avenue Pasteur 6, 1300 Wavre, Belgium
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4
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Rocker J, Zähringer TJB, Schmitz M, Opatz T, Kerzig C. Mechanistic investigations of polyaza[7]helicene in photoredox and energy transfer catalysis. Beilstein J Org Chem 2024; 20:1236-1245. [PMID: 38887585 PMCID: PMC11181280 DOI: 10.3762/bjoc.20.106] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2024] [Accepted: 05/16/2024] [Indexed: 06/20/2024] Open
Abstract
Organic photocatalysts frequently possess dual singlet and triplet photoreactivity and a thorough photochemical characterization is essential for efficient light-driven applications. In this article, the mode of action of a polyazahelicene catalyst (Aza-H) was investigated using laser flash photolysis (LFP). The study revealed that the chromophore can function as a singlet-state photoredox catalyst in the sulfonylation/arylation of styrenes and as a triplet sensitizer in energy transfer catalysis. The singlet lifetime is sufficiently long to exploit the exceptional excited state reduction potential for the activation of 4-cyanopyridine. Photoinduced electron transfer generating the radical cation was directly observed confirming the previously proposed mechanism of a three-component reaction. Several steps of the photoredox cycle were investigated separately, providing deep insights into the complex mechanism. The triplet-excited Aza-H, which was studied with quantitative LFP, is formed with a quantum yield of 0.34. The pronounced triplet formation was exploited for the isomerization reaction of (E)-stilbene to the Z-isomer and the cyclization of cinnamyl chloride. Catalyst degradation mainly occurs through the long-lived Aza-H triplet (28 µs), but the photostability is greatly increased when the triplet efficiently reacts in a catalytic cycle such that turnover numbers exceeding 4400 are achievable with this organocatalyst.
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Affiliation(s)
- Johannes Rocker
- Department of Chemistry Johannes Gutenberg University, Duesbergweg 10–14, 55128 Mainz, Germany
| | - Till J B Zähringer
- Department of Chemistry Johannes Gutenberg University, Duesbergweg 10–14, 55128 Mainz, Germany
| | - Matthias Schmitz
- Department of Chemistry Johannes Gutenberg University, Duesbergweg 10–14, 55128 Mainz, Germany
| | - Till Opatz
- Department of Chemistry Johannes Gutenberg University, Duesbergweg 10–14, 55128 Mainz, Germany
| | - Christoph Kerzig
- Department of Chemistry Johannes Gutenberg University, Duesbergweg 10–14, 55128 Mainz, Germany
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5
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Sau SC, Schmitz M, Burdenski C, Baumert M, Antoni PW, Kerzig C, Hansmann MM. Dicationic Acridinium/Carbene Hybrids as Strongly Oxidizing Photocatalysts. J Am Chem Soc 2024; 146:3416-3426. [PMID: 38266168 DOI: 10.1021/jacs.3c12766] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2024]
Abstract
A new design concept for organic, strongly oxidizing photocatalysts is described based upon dicationic acridinium/carbene hybrids. A highly modular synthesis of such hybrids is presented, and the dications are utilized as novel, tailor-made photoredox catalysts in the direct oxidative C-N coupling. Under optimized conditions, benzene and even electron-deficient arenes can be oxidized and coupled with a range of N-heterocycles in high to excellent yields with a single low-energy photon per catalytic turnover, while commonly used acridinium photocatalysts are not able to perform the challenging oxidation step. In contrast to traditional photocatalysts, the hybrid photocatalysts reported here feature a reversible two-electron redox system with regular or inverted redox potentials for the two-electron transfer. The different oxidation states could be isolated and structurally characterized supported by NMR, EPR, and X-ray analysis. Mechanistic experiments employing time-resolved emission and transient absorption spectroscopy unambiguously reveal the outstanding excited-state potential of our best-performing catalyst (+2.5 V vs SCE), and they provide evidence for mechanistic key steps and intermediates.
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Affiliation(s)
- Samaresh C Sau
- Fakultät für Chemie und Chemische Biologie, Technische Universität Dortmund, Otto-Hahn-Str. 6, Dortmund 44227, Germany
| | - Matthias Schmitz
- Department of Chemistry, Johannes Gutenberg University Mainz, Duesbergweg 10-14, Mainz 55128, Germany
| | - Chris Burdenski
- Fakultät für Chemie und Chemische Biologie, Technische Universität Dortmund, Otto-Hahn-Str. 6, Dortmund 44227, Germany
| | - Marcel Baumert
- Fakultät für Chemie und Chemische Biologie, Technische Universität Dortmund, Otto-Hahn-Str. 6, Dortmund 44227, Germany
| | - Patrick W Antoni
- Fakultät für Chemie und Chemische Biologie, Technische Universität Dortmund, Otto-Hahn-Str. 6, Dortmund 44227, Germany
| | - Christoph Kerzig
- Department of Chemistry, Johannes Gutenberg University Mainz, Duesbergweg 10-14, Mainz 55128, Germany
| | - Max M Hansmann
- Fakultät für Chemie und Chemische Biologie, Technische Universität Dortmund, Otto-Hahn-Str. 6, Dortmund 44227, Germany
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6
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Zähringer TJB, Wienhold M, Gilmour R, Kerzig C. Direct Observation of Triplet States in the Isomerization of Alkenylboronates by Energy Transfer Catalysis. J Am Chem Soc 2023; 145:21576-21586. [PMID: 37729087 DOI: 10.1021/jacs.3c07678] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/22/2023]
Abstract
Alkenylboronates are versatile building blocks for stereocontrolled synthesis owing to the traceless nature of the boron group that can be leveraged to achieve highly selective geometric isomerization. Using thioxanthone as an inexpensive photocatalyst, the photoisomerization of these species continues to provide an expansive platform for stereodivergent synthesis, particularly in the construction of bioactive polyenes. Although mechanistic investigations are consistent with light-driven energy transfer, direct experimental evidence remains conspicuously absent. Herein, we report a rigorous mechanistic investigation using two widely used alkenylboronates alongside relevant reference compounds. Through the combination of irradiation experiments, transient absorption spectroscopic studies, kinetic modeling, and DFT calculations with all isomers of the model compounds, it has been possible to unequivocally detect and characterize the perpendicular triplet generated by energy transfer. Our results serve not only as a blueprint for mechanistic studies that are challenging with organic sensitizers, but these guidelines delineated have also enabled the development of more sustainable reaction conditions: for the first time, efficient organocatalytic isomerization under sunlight irradiation has become feasible.
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Affiliation(s)
- Till J B Zähringer
- Department of Chemistry, Johannes Gutenberg University Mainz, Duesbergweg 10-14, 55128 Mainz, Germany
| | - Max Wienhold
- Organisch-Chemisches Institut,Westfälische Wilhelms-Universität Münster, Correnstraβe 36, 48149 Münster, Germany
| | - Ryan Gilmour
- Organisch-Chemisches Institut,Westfälische Wilhelms-Universität Münster, Correnstraβe 36, 48149 Münster, Germany
- Cells in Motion (CiM) Interfaculty Center, Röntgenstraβe 16, 48149 Münster, Germany
| | - Christoph Kerzig
- Department of Chemistry, Johannes Gutenberg University Mainz, Duesbergweg 10-14, 55128 Mainz, Germany
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7
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Bertrams MS, Hermainski K, Mörsdorf JM, Ballmann J, Kerzig C. Triplet quenching pathway control with molecular dyads enables the identification of a highly oxidizing annihilator class. Chem Sci 2023; 14:8583-8591. [PMID: 37592982 PMCID: PMC10430750 DOI: 10.1039/d3sc01725g] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2023] [Accepted: 07/15/2023] [Indexed: 08/19/2023] Open
Abstract
Metal complex - arene dyads typically act as more potent triplet energy donors compared to their parent metal complexes, which is frequently exploited for increasing the efficiencies of energy transfer applications. Using unexplored dicationic phosphonium-bridged ladder stilbenes (P-X2+) as quenchers, we exclusively observed photoinduced electron transfer photochemistry with commercial organic photosensitizers and photoactive metal complexes. In contrast, the corresponding pyrene dyads of the tested ruthenium complexes with the very same metal complex units efficiently sensitize the P-X2+ triplets. The long-lived and comparatively redox-inert pyrene donor triplet in the dyads thus provides an efficient access to acceptor triplet states that are otherwise very tricky to obtain. This dyad-enabled control over the quenching pathway allowed us to explore the P-X2+ photochemistry in detail using laser flash photolysis. The P-X2+ triplet undergoes annihilation producing the corresponding excited singlet, which is an extremely strong oxidant (+2.3 V vs. NHE) as demonstrated by halide quenching experiments. This behavior was observed for three P2+ derivatives allowing us to add a novel basic structure to the very limited number of annihilators for sensitized triplet-triplet annihilation in neat water.
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Affiliation(s)
- Maria-Sophie Bertrams
- Department of Chemistry, Johannes Gutenberg University Mainz Duesbergweg 10-14 55128 Mainz Germany
| | - Katharina Hermainski
- Department of Chemistry, Johannes Gutenberg University Mainz Duesbergweg 10-14 55128 Mainz Germany
| | - Jean-Marc Mörsdorf
- Anorganisch-Chemisches Institut, Universität Heidelberg Im Neuenheimer Feld 276 69120 Heidelberg Germany
| | - Joachim Ballmann
- Anorganisch-Chemisches Institut, Universität Heidelberg Im Neuenheimer Feld 276 69120 Heidelberg Germany
| | - Christoph Kerzig
- Department of Chemistry, Johannes Gutenberg University Mainz Duesbergweg 10-14 55128 Mainz Germany
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8
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Shen Y, Liu S, Lu L, Zhu C, Fang Q, Liu R, Shen Y, Song S. Pyridine-linked covalent triazine frameworks with bidirectional electron donor-acceptor for efficient organic pollution removal. JOURNAL OF HAZARDOUS MATERIALS 2023; 444:130428. [PMID: 36435039 DOI: 10.1016/j.jhazmat.2022.130428] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/17/2022] [Revised: 11/01/2022] [Accepted: 11/16/2022] [Indexed: 06/16/2023]
Abstract
Simultaneous regulation of adsorption and photocatalytic performance of covalent triazine frameworks (CTFs) to achieve efficient control of organic pollution in water is a promising strategy, but remains a formidable challenge. Herein, pyridine linkers were innovatively introduced into pristine CTF (p-CTF) and the bidirectional electron donor-acceptor (EDA) system of contaminant-to-pyridine and pyridine-to-triazine was constructed inside. Experimental results combined with theoretical calculations revealed that pyridine units with π-deficient properties performed as electron acceptors and electron donors in the adsorption and photocatalytic processes, respectively. This special structure provided a directional pathway for electron transfer, which endowed CTFs with excellent adsorption and photocatalytic properties. Compared to p-CTF, pyridine-linked CTF (M-CTF) showed a 16-fold increase in adsorption capacity for naphthalene (973.4 μmol·g-1). Benefiting from the optimized light absorption and electron transfer form (n → π*transition), M-CTF exhibited high regeneration efficiency after adsorption of both bisphenol A (94 % after 4 cycles) and naphthalene (95 % after 4 cycles). Besides, the removal performance of organic micropollutants from natural water showed a great advantage thanks to the bidirectional EDA system. Overall, the present study provides new insights into the optimization of electronic structures for carbon-based environmental functional materials applied to organic pollution control in water.
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Affiliation(s)
- Yi Shen
- College of Environment, Zhejiang University of Technology, Hangzhou 310032, PR China.
| | - Shasha Liu
- College of Environment, Zhejiang University of Technology, Hangzhou 310032, PR China
| | - Lun Lu
- State Environmental Protection Key Laboratory of Environmental Pollution Health Risk Assessment, South China Institute of Environmental Sciences, Ministry of Ecology and Environment, Guangzhou 510655, PR China
| | - Chao Zhu
- College of Environment, Zhejiang University of Technology, Hangzhou 310032, PR China; College of Chemical Engineering, Zhejiang University of Technology, Hangzhou 310032, PR China.
| | - Qile Fang
- Advanced Institute of Natural Sciences, Beijing Normal University at Zhuhai, Zhuhai 519087, PR China
| | - Renlan Liu
- College of Life and Environmental Science, Wenzhou University, Wenzhou 325035, PR China
| | - Yixin Shen
- College of Environment, Zhejiang University of Technology, Hangzhou 310032, PR China
| | - Shuang Song
- College of Environment, Zhejiang University of Technology, Hangzhou 310032, PR China
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10
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Bürgin TH, Glaser F, Wenger OS. Shedding Light on the Oxidizing Properties of Spin-Flip Excited States in a Cr III Polypyridine Complex and Their Use in Photoredox Catalysis. J Am Chem Soc 2022; 144:14181-14194. [PMID: 35913126 PMCID: PMC9376921 DOI: 10.1021/jacs.2c04465] [Citation(s) in RCA: 20] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
![]()
The photoredox activity of well-known RuII complexes
stems from metal-to-ligand charge transfer (MLCT) excited states,
in which a ligand-based electron can initiate chemical reductions
and a metal-centered hole can trigger oxidations. CrIII polypyridines show similar photoredox properties, although they
have fundamentally different electronic structures. Their photoactive
excited state is of spin-flip nature, differing from the electronic
ground state merely by a change of one electron spin, but with otherwise
identical d-orbital occupancy. We find that the driving-force dependence
for photoinduced electron transfer from 10 different donors to a spin-flip
excited state of a CrIII complex is very similar to that
for a RuII polypyridine, and thereby validate the concept
of estimating the redox potential of d3 spin-flip excited
states in analogous manner as for the MLCT states of d6 compounds. Building on this insight, we use our CrIII complex for photocatalytic reactions not previously explored with
this compound class, including the aerobic bromination of methoxyaryls,
oxygenation of 1,1,2,2-tetraphenylethylene, aerobic hydroxylation
of arylboronic acids, and the vinylation of N-phenyl
pyrrolidine. This work contributes to understanding the fundamental
photochemical properties of first-row transition-metal complexes in
comparison to well-explored precious-metal-based photocatalysts.
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Affiliation(s)
- Tobias H Bürgin
- Department of Chemistry, University of Basel, St. Johanns-Ring 19, 4056 Basel, Switzerland
| | - Felix Glaser
- Department of Chemistry, University of Basel, St. Johanns-Ring 19, 4056 Basel, Switzerland
| | - Oliver S Wenger
- Department of Chemistry, University of Basel, St. Johanns-Ring 19, 4056 Basel, Switzerland
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Sell AC, Wetzel JC, Schmitz M, Maijenburg AW, Woltersdorf G, Naumann R, Kerzig C. Water-soluble ruthenium complex-pyrene dyads with extended triplet lifetimes for efficient energy transfer applications. Dalton Trans 2022; 51:10799-10808. [PMID: 35788236 DOI: 10.1039/d2dt01157c] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Long triplet lifetimes of excited photosensitizers are essential for efficient energy transfer reactions in water, given that the concentrations of dissolved oxygen and suitable acceptors in aqueous media are typically much lower than in organic solvents. Herein, we report the design, synthesis and photochemical characterization of two structurally related water-soluble ruthenium complex-based dyads decorated with a covalently attached pyrene chromophore. The triplet energy of the latter is slightly below that of the metal complex enabling a so-called triplet reservoir and excited-state lifetime extensions of up to two orders of magnitude. The diimine co-ligands, which can be modified easily, have a major impact on both the ultrafast intramolecular energy transfer (iEnT) kinetics upon excitation with visible light and the lifetime of the resulting long-lived pyrene triplet. The phenanthroline-containing dyad shows fast triplet pyrene formation (25 ps) and an exceptionally long triplet lifetime beyond 50 microseconds in neat water. The iEnT process via the Dexter mechanism is slower by a factor of two when bipyridine co-ligands are employed, which is rationalized by a poor orbital overlap. Both dyads are very efficient sensitizers for the formation of singlet oxygen in air-saturated water as well as for the bimolecular generation of anthracene triplets that are key intermediates in upconversion mechanisms. This is demonstrated by the 5-hydroxymethylfurfural oxidation, which yields completely different main products depending on the pH value of the aqueous solution, as an initial application-related experiment and by time-resolved spectroscopy. Our findings are important in the greater contexts of photocatalysis and energy conversion in the "green" solvent water.
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Affiliation(s)
- Arne C Sell
- Department of Chemistry, Johannes Gutenberg University Mainz, Duesbergweg 10-14, 55128 Mainz, Germany.
| | - Julius C Wetzel
- Department of Chemistry, Johannes Gutenberg University Mainz, Duesbergweg 10-14, 55128 Mainz, Germany.
| | - Matthias Schmitz
- Department of Chemistry, Johannes Gutenberg University Mainz, Duesbergweg 10-14, 55128 Mainz, Germany.
| | - A Wouter Maijenburg
- Center for Innovation Competence SiLi-Nano, Martin-Luther-University Halle-Wittenberg, Karl-Freiherr-von-Fritsch-Straße 3, 06120 Halle, Germany
| | - Georg Woltersdorf
- Institute of Physics, Martin-Luther-University Halle-Wittenberg, Von-Danckelmann-Platz 3, 06120 Halle, Germany
| | - Robert Naumann
- Department of Chemistry, Johannes Gutenberg University Mainz, Duesbergweg 10-14, 55128 Mainz, Germany. .,Center for Innovation Competence SiLi-Nano, Martin-Luther-University Halle-Wittenberg, Karl-Freiherr-von-Fritsch-Straße 3, 06120 Halle, Germany
| | - Christoph Kerzig
- Department of Chemistry, Johannes Gutenberg University Mainz, Duesbergweg 10-14, 55128 Mainz, Germany.
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12
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Sinha N, Pfund B, Wegeberg C, Prescimone A, Wenger OS. Cobalt(III) Carbene Complex with an Electronic Excited-State Structure Similar to Cyclometalated Iridium(III) Compounds. J Am Chem Soc 2022; 144:9859-9873. [PMID: 35623627 PMCID: PMC9490849 DOI: 10.1021/jacs.2c02592] [Citation(s) in RCA: 21] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
![]()
Many organometallic
iridium(III) complexes have photoactive excited
states with mixed metal-to-ligand and intraligand charge transfer
(MLCT/ILCT) character, which form the basis for numerous applications
in photophysics and photochemistry. Cobalt(III) complexes with analogous
MLCT excited-state properties seem to be unknown yet, despite the
fact that iridium(III) and cobalt(III) can adopt identical low-spin
d6 valence electron configurations due to their close chemical
relationship. Using a rigid tridentate chelate ligand (LCNC), in which a central amido π-donor is flanked by two σ-donating
N-heterocyclic carbene subunits, we obtained a robust homoleptic complex
[Co(LCNC)2](PF6), featuring a photoactive
excited state with substantial MLCT character. Compared to the vast
majority of isoelectronic iron(II) complexes, the MLCT state of [Co(LCNC)2](PF6) is long-lived because it
does not deactivate as efficiently into lower-lying metal-centered
excited states; furthermore, it engages directly in photoinduced electron
transfer reactions. The comparison with [Fe(LCNC)2](PF6), as well as structural, electrochemical, and UV–vis
transient absorption studies, provides insight into new ligand design
principles for first-row transition-metal complexes with photophysical
and photochemical properties reminiscent of those known from the platinum
group metals.
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Affiliation(s)
- Narayan Sinha
- Department of Chemistry, University of Basel, St. Johanns-Ring 19, 4056 Basel, Switzerland
| | - Björn Pfund
- Department of Chemistry, University of Basel, St. Johanns-Ring 19, 4056 Basel, Switzerland
| | - Christina Wegeberg
- Department of Chemistry, University of Basel, St. Johanns-Ring 19, 4056 Basel, Switzerland
| | - Alessandro Prescimone
- Department of Chemistry, University of Basel, BPR 1096, Mattenstrasse 24a, 4058 Basel, Switzerland
| | - Oliver S Wenger
- Department of Chemistry, University of Basel, St. Johanns-Ring 19, 4056 Basel, Switzerland
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13
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DiLuzio S, Connell TU, Mdluli V, Kowalewski JF, Bernhard S. Understanding Ir(III) Photocatalyst Structure-Activity Relationships: A Highly Parallelized Study of Light-Driven Metal Reduction Processes. J Am Chem Soc 2022; 144:1431-1444. [PMID: 35025486 DOI: 10.1021/jacs.1c12059] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
High-throughput synthesis and screening methods were used to measure the photochemical activity of 1440 distinct heteroleptic [Ir(C^N)2(N^N)]+ complexes for the photoreduction of Sn(II) and Zn(II) cations to their corresponding neutral metals. Kinetic data collection was carried out using home-built photoreactors and measured initial rates, obtained through an automated fitting algorithm, spanned between 0-120 μM/s for Sn(0) deposition and 0-90 μM/s for Zn(0) deposition. Photochemical reactivity was compared to photophysical properties previously measured such as deaerated excited state lifetime and emission spectral data for these same complexes; however, no clear correlations among these features were observed. A formal photochemical rate law was then developed to help elucidate the observed reactivity. Initial rates were found to be directly correlated to the product of incident photon flux with three reaction elementary efficiencies: (1) the fraction of light absorbed by the photocatalyst, (2) the fraction of excited state species that are quenched by the electron donor, and (3) the cage escape efficiency. The most active catalysts exhibit high efficiencies for all three steps, and catalyst engineering requirements to maximize these elementary efficiencies were postulated. The kinetic treatment provided the mechanistic information needed to decipher the observed structure/function trends in the high-throughput work.
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Affiliation(s)
- Stephen DiLuzio
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
| | - Timothy U Connell
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
| | - Velabo Mdluli
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
| | - Jakub F Kowalewski
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
| | - Stefan Bernhard
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
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Wegeberg C, Wenger OS. Luminescent First-Row Transition Metal Complexes. JACS AU 2021; 1:1860-1876. [PMID: 34841405 PMCID: PMC8611671 DOI: 10.1021/jacsau.1c00353] [Citation(s) in RCA: 108] [Impact Index Per Article: 36.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/13/2021] [Indexed: 05/25/2023]
Abstract
Precious and rare elements have traditionally dominated inorganic photophysics and photochemistry, but now we are witnessing a paradigm shift toward cheaper and more abundant metals. Even though emissive complexes based on selected first-row transition metals have long been known, recent conceptual breakthroughs revealed that a much broader range of elements in different oxidation states are useable for this purpose. Coordination compounds of V, Cr, Mn, Fe, Co, Ni, and Cu now show electronically excited states with unexpected reactivity and photoluminescence behavior. Aside from providing a compact survey of the recent conceptual key advances in this dynamic field, our Perspective identifies the main design strategies that enabled the discovery of fundamentally new types of 3d-metal-based luminophores and photosensitizers operating in solution at room temperature.
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15
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Bertrams MS, Kerzig C. Converting p-terphenyl into a novel organo-catalyst for LED-driven energy and electron transfer photoreactions in water. Chem Commun (Camb) 2021; 57:6752-6755. [PMID: 34143166 DOI: 10.1039/d1cc01947c] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
p-Terphenyl is a potent photoredox catalyst under UV-irradiation. Aiming for more sustainable reaction conditions, we added two sulfonate groups to this key structure to achieve water solubility and incorporated an SO2-bridge thereby shifting the absorption spectrum towards the visible. The resulting photocatalyst shows unexpected triplet reactivity in several test reactions.
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Affiliation(s)
- Maria-Sophie Bertrams
- Department of Chemistry, Johannes Gutenberg University Mainz, Duesbergweg 10-14, 55128 Mainz, Germany.
| | - Christoph Kerzig
- Department of Chemistry, Johannes Gutenberg University Mainz, Duesbergweg 10-14, 55128 Mainz, Germany.
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16
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Neumann S, Wenger OS, Kerzig C. Controlling Spin-Correlated Radical Pairs with Donor-Acceptor Dyads: A New Concept to Generate Reduced Metal Complexes for More Efficient Photocatalysis. Chemistry 2021; 27:4115-4123. [PMID: 33274791 PMCID: PMC7986886 DOI: 10.1002/chem.202004638] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2020] [Revised: 12/02/2020] [Indexed: 12/30/2022]
Abstract
One-electron reduced metal complexes derived from photoactive ruthenium or iridium complexes are important intermediates for substrate activation steps in photoredox catalysis and for the photocatalytic generation of solar fuels. However, owing to the heavy atom effect, direct photochemical pathways to these key intermediates suffer from intrinsic efficiency problems resulting from rapid geminate recombination of radical pairs within the so-called solvent cage. In this study, we prepared and investigated molecular dyads capable of producing reduced metal complexes via an indirect pathway relying on a sequence of energy and electron transfer processes between a Ru complex and a covalently connected anthracene moiety. Our test reaction to establish the proof-of-concept is the photochemical reduction of ruthenium(tris)bipyridine by the ascorbate dianion as sacrificial donor in aqueous solution. The photochemical key step in the Ru-anthracene dyads is the reduction of a purely organic (anthracene) triplet excited state by the ascorbate dianion, yielding a spin-correlated radical pair whose (unproductive) recombination is strongly spin-forbidden. By carrying out detailed laser flash photolysis investigations, we provide clear evidence for the indirect reduced metal complex generation mechanism and show that this pathway can outperform the conventional direct metal complex photoreduction. The further optimization of our approach involving relatively simple molecular dyads might result in novel photocatalysts that convert substrates with unprecedented quantum yields.
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Affiliation(s)
- Svenja Neumann
- Department of ChemistryUniversity of BaselSt. Johanns-Ring 194056BaselSwitzerland
| | - Oliver S. Wenger
- Department of ChemistryUniversity of BaselSt. Johanns-Ring 194056BaselSwitzerland
| | - Christoph Kerzig
- Department of ChemistryUniversity of BaselSt. Johanns-Ring 194056BaselSwitzerland
- Department of ChemistryJohannes Gutenberg University MainzDuesbergweg 10—1455128MainzGermany
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