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Doeven EH, Connell TU, Sinha N, Wenger OS, Francis PS. Electrochemiluminescence of a First-Row d 6 Transition Metal Complex. Angew Chem Int Ed Engl 2024; 63:e202319047. [PMID: 38519420 DOI: 10.1002/anie.202319047] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2023] [Revised: 03/12/2024] [Accepted: 03/22/2024] [Indexed: 03/24/2024]
Abstract
We report the electrochemiluminescence (ECL) of a 3d6 Cr(0) complex ([Cr(LMes)3]; λem=735 nm) with comparable photophysical properties to those of ECL-active complexes of 4d6 or 5d6 precious metal ions. The electrochemical potentials of [Cr(LMes)3] are more negative than those of [Ir(ppy)3] and render the [Cr(LMes)3]* excited state inaccessible through conventional co-reactant ECL with tri-n-propylamine or oxalate. ECL can be obtained, however, through the annihilation route in which potentials sufficient to oxidise and reduce the luminophore are alternately applied. When combined with [Ir(ppy)3] (λem=520 nm), the annihilation ECL of [Cr(LMes)3] was greatly enhanced whereas that of [Ir(ppy)3] was diminished. Under appropriate conditions, the relative intensities of the two spectrally distinct emissions can be controlled through the applied potentials. From this starting point for ECL with 3d6 metal complexes, we discuss some directions for future development.
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Affiliation(s)
- Egan H Doeven
- Centre for Sustainable Bioproducts, Faculty of Science, Engineering and Built Environment, Deakin University Waurn Ponds, Victoria, 3216, Australia
| | - Timothy U Connell
- Centre for Sustainable Bioproducts, Faculty of Science, Engineering and Built Environment, Deakin University Waurn Ponds, Victoria, 3216, Australia
| | - Narayan Sinha
- Department of Chemistry, University of Basel, St. Johanns-Ring 19, 4056, Basel, Switzerland
- School of Chemical Sciences, Indian Institute of Technology (IIT) Mandi Kamand, Mandi, 175075, Himachal Pradesh, India
| | - Oliver S Wenger
- Department of Chemistry, University of Basel, St. Johanns-Ring 19, 4056, Basel, Switzerland
| | - Paul S Francis
- Centre for Sustainable Bioproducts, Faculty of Science, Engineering and Built Environment, Deakin University Waurn Ponds, Victoria, 3216, Australia
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Kim D, Dang VQ, Teets TS. Improved transition metal photosensitizers to drive advances in photocatalysis. Chem Sci 2023; 15:77-94. [PMID: 38131090 PMCID: PMC10732135 DOI: 10.1039/d3sc04580c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2023] [Accepted: 11/22/2023] [Indexed: 12/23/2023] Open
Abstract
To function effectively in a photocatalytic application, a photosensitizer's light absorption, excited-state lifetime, and redox potentials, both in the ground state and excited state, are critically important. The absorption profile is particularly relevant to applications involving solar harvesting, whereas the redox potentials and excited-state lifetimes determine the thermodynamics, kinetics, and quantum yields of photoinduced redox processes. This perspective article focuses on synthetic inorganic and organometallic approaches to optimize these three characteristics of transition-metal based photosensitizers. We include our own work in these areas, which has focused extensively on exceptionally strong cyclometalated iridium photoreductants that enable challenging reductive photoredox transformations on organic substrates, and more recent work which has led to improved solar harvesting in charge-transfer copper(i) chromophores, an emerging class of earth-abundant compounds particularly relevant to solar-energy applications. We also extensively highlight many other complementary strategies for optimizing these parameters and highlight representative examples from the recent literature. It remains a significant challenge to simultaneously optimize all three of these parameters at once, since improvements in one often come at the detriment of the others. These inherent trade-offs and approaches to obviate or circumvent them are discussed throughout.
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Affiliation(s)
- Dooyoung Kim
- University of Houston, Department of Chemistry 3585 Cullen Blvd. Room 112 Houston TX 77204-5003 USA
| | - Vinh Q Dang
- University of Houston, Department of Chemistry 3585 Cullen Blvd. Room 112 Houston TX 77204-5003 USA
| | - Thomas S Teets
- University of Houston, Department of Chemistry 3585 Cullen Blvd. Room 112 Houston TX 77204-5003 USA
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Yu L, Lee KW, Zhao YQ, Xu Y, Zhou Y, Li M, Kim JS. Metal Modulation: An Effortless Tactic for Refining Photoredox Catalysis in Living Cells. Inorg Chem 2023; 62:18767-18778. [PMID: 37905835 DOI: 10.1021/acs.inorgchem.3c03284] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2023]
Abstract
The remarkable impact of photoredox catalytic chemistries has sparked a wave of innovation, opening doors to novel biotechnologies in the realm of catalytic antitumor therapy. Yet, the quest for novel photoredox catalysts (PCs) suitable for living systems, or the enhancement of catalytic efficacy in existing biocompatible PC systems, persists as a formidable challenge. Within this context, we introduce a readily applicable metal modulation strategy that significantly augments photoredox catalysis within living cells, exemplified by a set of metalloporphyrin complexes termed M-TCPPs (M = Zn, Mn, Ni, Co, Cu). Among these complexes, Zn-TCPP emerges as an exceptional catalyst, displaying remarkable photocatalytic activity in the oxidation of nicotinamide adenine dinucleotide (NADH), nicotinamide adenine dinucleotide phosphate (NADPH), and specific amino acids. Notably, comprehensive investigations reveal that Zn-TCPP's superior catalytic prowess primarily arises from the establishment of an efficient oxidative cycle for PC, in contrast to previously reported PCs engaged in reductive cycles. Moreover, theoretical calculations illuminate that amplified intersystem crossing rates and geometry alterations in Zn-TCPP contribute to its heightened photocatalytic performance. In vitro studies demonstrated that Zn-TCPP exhibits therapeutic potential and is found to be effective for photocatalytic antitumor therapy in both glioblastoma G98T cells and 3D multicellular spheroids. This study underscores the transformative role of "metal modulation" in advancing high-performance PCs for catalytic antitumor therapy, marking a significant stride toward the realization of this innovative therapeutic approach.
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Affiliation(s)
- Le Yu
- Department of Chemistry, Korea University, Seoul 02841, Republic of Korea
| | - Kyung-Woo Lee
- Department of Chemistry, Korea University, Seoul 02841, Republic of Korea
| | - Yu-Qiang Zhao
- College of Chemical Science and Technology, Yunnan University, Kunming 650091, China
| | - Yunjie Xu
- Department of Chemistry, Korea University, Seoul 02841, Republic of Korea
| | - Ying Zhou
- College of Chemical Science and Technology, Yunnan University, Kunming 650091, China
| | - Mingle Li
- State Key Laboratory of Fine Chemicals, College of Materials Science and Engineering, Shenzhen University, Shenzhen 518060, China
| | - Jong Seung Kim
- Department of Chemistry, Korea University, Seoul 02841, Republic of Korea
- TheranoChem Incorporation, Seongbuk-gu, Seoul 02856, Republic of Korea
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Barth AT, Fajardo J, Sattler W, Winkler JR, Gray HB. Electronic Structures and Photoredox Chemistry of Tungsten(0) Arylisocyanides. Acc Chem Res 2023. [PMID: 37384787 DOI: 10.1021/acs.accounts.3c00184] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/01/2023]
Abstract
ConspectusThe high energy barriers associated with the reaction chemistry of inert substrates can be overcome by employing redox-active photocatalysts. Research in this area has grown exponentially over the past decade, as transition metal photosensitizers have been shown to mediate challenging organic transformations. Critical for the advancement of photoredox catalysis is the discovery, development, and study of complexes based on earth-abundant metals that can replace and/or complement established noble-metal-based photosensitizers.Recent work has focused on redox-active complexes of 3d metals, as photosensitizers containing these metals most likely would be scalable. Although low lying spin doublet ("spin flip") excited states of chromium(III) and metal-to-ligand charge transfer (MLCT) excited states of copper(I) have relatively long lifetimes, the electronic excited states of many other 3d metal complexes fall on dissociative potential energy surfaces, owing to the population of highly energetic σ-antibonding orbitals. Indeed, we and other investigators have shown that low lying spin singlet and triplet excited states of robust closed-shell metal complexes are too short-lived at room temperature to engage in bimolecular reactions in solutions. In principle, this problem could be overcome by designing and constructing 3d metal complexes containing strong field π-acceptor ligands, where thermally equilibrated MLCT or intraligand charge transfer excited states might fall well below the upper surfaces of dissociative 3d-3d states. Notably, such design elements have been exploited by investigators in very recent work on redox-active iron(II) systems. Another approach, one we have actively pursued, is to design and construct closed-shell complexes of earth-abundant 5d metals containing very strong π-acceptor ligands, where vertical excitation of 5d-5d excited states at the ground state geometry would require energies far above minima in the potential surfaces of MLCT excited states. As this requirement is met by tungsten(0) arylisocyanides, these complexes have been the focus of our work aimed at the development of robust redox-active photosensitizers.In the following Account, we review recent work on homoleptic tungsten(0) arylisocyanides. Originally reported by our group 45 years ago, W(CNAr)6 complexes have exceptionally large one- and two-photon absorption cross-sections. One- or two-photon excitation produces relatively long-lived (hundreds of nanoseconds to microsecond) MLCT excited states in high yields. These MLCT excited states, which are very strong reductants with E°(W+/*W0) = -2.2 to -3.0 V vs Fc[+/0], mediate photocatalysis of organic reactions with both visible and near-infrared (NIR) light. Here, we highlight design principles that led to the development of three generations of W(CNAr)6 photosensitizers; and we discuss likely steps in the mechanism of a prototypal W(CNAr)6-catalyzed base-promoted homolytic aromatic substitution reaction. Among the many potential applications of these very bright luminophores, two-photon imaging and two-photon-initiated polymerization are ones we plan to pursue.
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Affiliation(s)
- Alexandra T Barth
- Beckman Institute, California Institute of Technology, Pasadena, California 91125, United States
| | - Javier Fajardo
- Beckman Institute, California Institute of Technology, Pasadena, California 91125, United States
| | - Wesley Sattler
- Beckman Institute, California Institute of Technology, Pasadena, California 91125, United States
| | - Jay R Winkler
- Beckman Institute, California Institute of Technology, Pasadena, California 91125, United States
| | - Harry B Gray
- Beckman Institute, California Institute of Technology, Pasadena, California 91125, United States
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Sinha N, Wenger OS. Photoactive Metal-to-Ligand Charge Transfer Excited States in 3d 6 Complexes with Cr 0, Mn I, Fe II, and Co III. J Am Chem Soc 2023; 145:4903-4920. [PMID: 36808978 PMCID: PMC9999427 DOI: 10.1021/jacs.2c13432] [Citation(s) in RCA: 39] [Impact Index Per Article: 39.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/23/2023]
Abstract
Many coordination complexes and organometallic compounds with the 4d6 and 5d6 valence electron configurations have outstanding photophysical and photochemical properties, which stem from metal-to-ligand charge transfer (MLCT) excited states. This substance class makes extensive use of the most precious and least abundant metal elements, and consequently there has been a long-standing interest in first-row transition metal compounds with photoactive MLCT states. Semiprecious copper(I) with its completely filled 3d subshell is a relatively straightforward and well explored case, but in 3d6 complexes the partially filled d-orbitals lead to energetically low-lying metal-centered (MC) states that can cause undesirably fast MLCT excited state deactivation. Herein, we discuss recent advances made with isoelectronic Cr0, MnI, FeII, and CoIII compounds, for which long-lived MLCT states have become accessible over the past five years. Furthermore, we discuss possible future developments in the search for new first-row transition metal complexes with partially filled 3d subshells and photoactive MLCT states for next-generation applications in photophysics and photochemistry.
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Affiliation(s)
- Narayan Sinha
- 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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