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Garner MH, Blaskovits JT, Corminboeuf C. Double-bond delocalization in non-alternant hydrocarbons induces inverted singlet-triplet gaps. Chem Sci 2023; 14:10458-10466. [PMID: 37800005 PMCID: PMC10548509 DOI: 10.1039/d3sc03409g] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2023] [Accepted: 09/06/2023] [Indexed: 10/07/2023] Open
Abstract
Molecules where the first excited singlet state is lower in energy than the first excited triplet state have the potential to revolutionize OLEDs. This inverted singlet-triplet gap violates Hund's rule and currently there are only a few molecules which are known to have this property. Here, we screen the complete set of non-alternant hydrocarbons consisting of 5-, 6-, 7-membered rings fused into two-, three- and four-ring polycyclic systems. We identify several molecules where the symmetry of the ground-state structure is broken due to bond-length alternation. Through symmetry-constrained optimizations we identify several molecular cores where the singlet-triplet gap is inverted when the structure is in a higher symmetry, pentalene being a known example. We uncover a strategy to stabilize the molecular cores into their higher-symmetry structures with electron donors or acceptors. We design several substituted pentalenes, s-indacenes, and indeno[1,2,3-ef]heptalenes with inverted gaps, among which there are several synthetically known examples. In contrast to known inverted gap emitters, we identify the double-bond delocalized structure of their conjugated cores as the necessary condition to achieve the inverted gap. This strategy enables chemical tuning and paves the way for the rational design of polycyclic hydrocarbons with inverted singlet-triplet gaps. These molecules are prospective emitters if their properties can be optimized for use in OLEDs.
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Affiliation(s)
- Marc H Garner
- Laboratory for Computational Molecular Design, Institute of Chemical Sciences and Engineering, École Polytechnique Fedéralé de Lausanne (EPFL) 1015 Lausanne Switzerland
| | - J Terence Blaskovits
- Laboratory for Computational Molecular Design, Institute of Chemical Sciences and Engineering, École Polytechnique Fedéralé de Lausanne (EPFL) 1015 Lausanne Switzerland
| | - Clémence Corminboeuf
- Laboratory for Computational Molecular Design, Institute of Chemical Sciences and Engineering, École Polytechnique Fedéralé de Lausanne (EPFL) 1015 Lausanne Switzerland
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2
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Hwang D, Wrigley LM, Lee M, Sobolewski AL, Domcke W, Schlenker CW. Local Hydrogen Bonding Determines Branching Pathways in Intermolecular Heptazine Photochemistry. J Phys Chem B 2023. [PMID: 37471476 DOI: 10.1021/acs.jpcb.3c01397] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/22/2023]
Abstract
Heptazine is the molecular core of the widely studied photocatalyst carbon nitride. By analyzing the excited-state intermolecular proton-coupled electron-transfer (PCET) reaction between a heptazine derivative and a hydrogen-atom donor substrate, we are able to spectroscopically identify the resultant heptazinyl reactive radical species on a picosecond time scale. We provide detailed spectroscopic characterization of the tri-anisole heptazine:4-methoxyphenol hydrogen-bonded intermolecular complex (TAHz:MeOPhOH), using femtosecond transient absorption spectroscopy and global analysis, to reveal distinct product absorption signatures at ∼520, 1250, and 1600 nm. We assign these product peaks to the hydrogenated TAHz radical (TAHzH•) based on control experiments utilizing 1,4-dimethoxybenzene (DMB), which initiates electron transfer without concomitant proton transfer, i.e., no excited-state PCET. Additional control experiments with radical quenchers, protonation agents, and UV-vis-NIR spectroelectrochemistry also corroborate our product peak assignments. These spectral assignments allowed us to monitor the influence of the local hydrogen-bonding environment on the resulting evolution of photochemical products from excited-state PCET of heptazines. We observe that the preassociation of heptazine with the substrate in solution is extremely sensitive to the hydrogen-bond-accepting character of the solvent. This sensitivity directly influences which product signatures we detect with time-resolved spectroscopy. The spectral signature of the TAHzH• radical assigned in this work will facilitate future in-depth analysis of heptazine and carbon nitride photochemistry. Our results may also be utilized for designing improved PCET-based photochemical systems that will require precise control over local molecular environments. Examples include applications such as preparative synthesis involving organic photoredox catalysis, on-site solar water purification, as well as photocatalytic water splitting and artificial photosynthesis.
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Affiliation(s)
- Doyk Hwang
- Department of Chemistry, University of Washington, Seattle, Washington 98195, United States
| | - Liam M Wrigley
- Department of Chemistry, University of Washington, Seattle, Washington 98195, United States
| | - Micah Lee
- Department of Chemistry, University of Washington, Seattle, Washington 98195, United States
| | | | - Wolfgang Domcke
- Department of Chemistry, Technical University of Munich, D-85747 Garching, Germany
| | - Cody W Schlenker
- Department of Chemistry, University of Washington, Seattle, Washington 98195, United States
- Molecular Engineering & Sciences Institute, University of Washington, Seattle, Washington 98195-1652, United States
- Clean Energy Institute, University of Washington, Seattle, Washington 98195-1653, United States
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3
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Terence Blaskovits J, Garner MH, Corminboeuf C. Symmetry-Induced Singlet-Triplet Inversions in Non-Alternant Hydrocarbons. Angew Chem Int Ed Engl 2023; 62:e202218156. [PMID: 36786076 DOI: 10.1002/anie.202218156] [Citation(s) in RCA: 14] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2022] [Revised: 02/09/2023] [Accepted: 02/13/2023] [Indexed: 02/15/2023]
Abstract
Molecules with inversion of the singlet and triplet excited-state energies are highly promising for the development of organic light-emitting diodes (OLEDs). To date, azaphenalenes are the only class of molecules where these inversions have been identified. Here, we screen a curated database of organic crystal structures to identify existing compounds for violations of Hund's rule in the lowest excited states. We identify two further classes with this behavior. The first, a class of zwitterions, has limited relevance to molecular emitters as the singlet-triplet inversions occur in the third excited singlet state. The second class consists of two D2h -symmetry non-alternant hydrocarbons, a fused azulene dimer and a bicalicene, whose lowest excited singlet states violate Hund's rule. Due to the connectivity of the polycyclic structure, they achieve this symmetry through aromatic stabilization. These hydrocarbons show promise as the next generation of building blocks for OLED emitters.
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Affiliation(s)
- J Terence Blaskovits
- Laboratory for Computational Molecular Design, Institute of Chemical Sciences and Engineering, École Polytechnique Fedéralé de Lausanne (EPFL), 1015, Lausanne, Switzerland
| | - Marc H Garner
- Laboratory for Computational Molecular Design, Institute of Chemical Sciences and Engineering, École Polytechnique Fedéralé de Lausanne (EPFL), 1015, Lausanne, Switzerland
| | - Clémence Corminboeuf
- Laboratory for Computational Molecular Design, Institute of Chemical Sciences and Engineering, École Polytechnique Fedéralé de Lausanne (EPFL), 1015, Lausanne, Switzerland
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4
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Oxygen-Doped Carbon Nitride for Enhanced Photocatalytic Activity in Visible-Light-Induced Decarboxylative Annulation Reactions. J Catal 2022. [DOI: 10.1016/j.jcat.2022.09.027] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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5
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Li J, Li Z, Liu H, Gong H, Zhang J, Yao Y, Guo Q. Organic molecules with inverted singlet-triplet gaps. Front Chem 2022; 10:999856. [PMID: 36092667 PMCID: PMC9448862 DOI: 10.3389/fchem.2022.999856] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2022] [Accepted: 08/01/2022] [Indexed: 11/13/2022] Open
Abstract
According to Hund’s multiplicity rule, the energy of the lowest excited triplet state (T1) is always lower than that of the lowest excited singlet state (S1) in organic molecules, resulting in a positive singlet-triplet energy gap (ΔEST). Therefore, the up-converted reverse intersystem crossing (RISC) from T1 to S1 is an endothermic process, which may lead to the quenching of long-lived triplet excitons in electroluminescence, and subsequently the reduction of device efficiency. Interestingly, organic molecules with inverted singlet-triplet (INVEST) gaps in violation of Hund’s multiplicity rule have recently come into the limelight. The unique feature has attracted extensive attention in the fields of organic optoelectronics and photocatalysis over the past few years. For an INVEST molecule possessing a higher T1 with respect to S1, namely a negative ΔEST, the down-converted RISC from T1 to S1 does not require thermal activation, which is possibly conducive to solving the problems of fast efficiency roll-off and short lifetime of organic light-emitting devices. By virtue of this property, INVEST molecules are recently regarded as a new generation of organic light-emitting materials. In this review, we briefly summarized the significant progress of INVEST molecules in both theoretical calculations and experimental studies, and put forward suggestions and expectations for future research.
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Affiliation(s)
- Jie Li
- College of Optoelectronic Engineering, Chengdu University of Information Technology, Chengdu, China
| | - Zhi Li
- College of Optoelectronic Engineering, Chengdu University of Information Technology, Chengdu, China
| | - Hui Liu
- College of Optoelectronic Engineering, Chengdu University of Information Technology, Chengdu, China
| | - Heqi Gong
- College of Optoelectronic Engineering, Chengdu University of Information Technology, Chengdu, China
| | - Jincheng Zhang
- College of Optoelectronic Engineering, Chengdu University of Information Technology, Chengdu, China
| | - Yali Yao
- School of Physics and Engineering Technology, Chengdu Normal University, Chengdu, China
| | - Qiang Guo
- College of Optoelectronic Engineering, Chengdu University of Information Technology, Chengdu, China
- *Correspondence: Qiang Guo,
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Dai T, Kiuchi H, Minamide H, Miyake Y, Inoki H, Sonoda Y, Tsutsumi J, Kanai K. Growth and characterization of melem hydrate crystals with a hydrogen-bonded heptazine framework. Phys Chem Chem Phys 2022; 24:13922-13934. [PMID: 35621074 DOI: 10.1039/d2cp00691j] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
In carbon nitride (CN) compounds, hydrogen bonds play a major role in cohesion, in addition to dispersion forces. The crystal structures of CN compounds produced via thermal polymerization are complex, but they possess unique and attractive features. Melem is a well-known building unit of CN compounds such as melon and g-C3N4, which have recently attracted attention as photocatalysts. Melem hydrate (Mh) forms hexagonal prismatic crystals that are sufficiently porous to accommodate small molecules. In this study, we grew and characterized single crystals of Mh and investigated their optical properties and hygroscopicity. By precisely adjusting the hydration conditions, we succeeded in growing a well-formed hexagonal prismatic single crystal of Mh (Mhr) with a length measuring several tens of micrometers. Furthermore, we discovered a parallelogram-shaped Mh single crystal (Mhp), which possessed a different crystal structure and optical properties from those of Mh and melem crystals. Although the crystal structure of Mh was greatly disrupted by dehydration, it exhibited hygroscopicity and could absorb moisture even in air, restoring the crystal structure of Mh. In addition, Mh demonstrated a high photoluminescence quantum yield and long lifetime delayed fluorescence, similar to melem crystal. The high quantum yield of Mh can be attributed to the effect of the strong anchoring of the melem molecule by several hydrogen bonds in the Mh crystal, since the strongly anchored molecule is less likely to undergo radiation-free deactivation due to the small displacement of atomic positions in the excited state after light absorption. The findings obtained in this study shed light not only on the application of CN compounds as photocatalysts, but also on a wider range of applications based on their optoelectronic functions.
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Affiliation(s)
- Tomonori Dai
- Department of Physics, Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan.
| | - Hiroki Kiuchi
- Department of Physics, Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan.
| | - Hiroki Minamide
- Department of Physics, Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan.
| | - Yuto Miyake
- Department of Physics, Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan.
| | - Hiroya Inoki
- Department of Physics, Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan.
| | - Yoriko Sonoda
- Research Institute for Advanced Electronics and Photonics, National Institute of Advanced Industrial Science and Technology (AIST), Higashi 1-1-1, 305-8565 Tsukuba, Ibaraki, Japan
| | - Jun'ya Tsutsumi
- Research Institute for Advanced Electronics and Photonics, National Institute of Advanced Industrial Science and Technology (AIST), Higashi 1-1-1, 305-8565 Tsukuba, Ibaraki, Japan
| | - Kaname Kanai
- Department of Physics, Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan.
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Poletti L, Ragno D, Bortolini O, Presini F, Pesciaioli F, Carli S, Caramori S, Molinari A, Massi A, Di Carmine G. Photoredox Cross-Dehydrogenative Coupling of N-Aryl Glycines Mediated by Mesoporous Graphitic Carbon Nitride: An Environmentally Friendly Approach to the Synthesis of Non-Proteinogenic α-Amino Acids (NPAAs) Decorated with Indoles. J Org Chem 2022; 87:7826-7837. [PMID: 35621232 PMCID: PMC9207928 DOI: 10.1021/acs.joc.2c00474] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
![]()
Indole-decorated
glycine derivatives are prepared through an environmentally
benign cross-dehydrogenative coupling between N-aryl
glycine analogues and indoles (yield of ≤81%). Merging heterogeneous
organocatalysis and photocatalysis, C–H functionalization has
been achieved by selective C-2 oxidation of N-aryl
glycines to afford the electrophilic imine followed by Friedel–Crafts
alkylation with indole. The sustainability of the process has been
taken into account in the reaction design through the implementation
of a metal-free recyclable heterogeneous photocatalyst and a green
reaction medium. Scale-up of the benchmark reaction (gram scale, yield
of 69%) and recycling experiments (over seven runs without a loss
of efficiency) have been performed to prove the robustness of the
protocol. Finally, mechanistic studies were conducted employing electron
paramagnetic resonance spectroscopy to unveil the roles of the photocatalyst
and oxygen in the formation of odd-electron species.
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Affiliation(s)
- Lorenzo Poletti
- Department of Chemical, Pharmaceutical and Agricultural Sciences, University of Ferrara, Via L. Borsari, 46, 44121 Ferrara, Italy
| | - Daniele Ragno
- Department of Chemical, Pharmaceutical and Agricultural Sciences, University of Ferrara, Via L. Borsari, 46, 44121 Ferrara, Italy
| | - Olga Bortolini
- Department of Environmental and Prevention Sciences, University of Ferrara, Via L. Borsari, 46, 44121 Ferrara, Italy
| | - Francesco Presini
- Department of Chemical, Pharmaceutical and Agricultural Sciences, University of Ferrara, Via L. Borsari, 46, 44121 Ferrara, Italy
| | - Fabio Pesciaioli
- Department of Physical and Chemical Sciences, Università degli Studi dell'Aquila, Via Vetoio, 42, 67100 L'Aquila, Italy
| | - Stefano Carli
- Department of Environmental and Prevention Sciences, University of Ferrara, Via L. Borsari, 46, 44121 Ferrara, Italy
| | - Stefano Caramori
- Department of Chemical, Pharmaceutical and Agricultural Sciences, University of Ferrara, Via L. Borsari, 46, 44121 Ferrara, Italy
| | - Alessandra Molinari
- Department of Chemical, Pharmaceutical and Agricultural Sciences, University of Ferrara, Via L. Borsari, 46, 44121 Ferrara, Italy
| | - Alessandro Massi
- Department of Chemical, Pharmaceutical and Agricultural Sciences, University of Ferrara, Via L. Borsari, 46, 44121 Ferrara, Italy
| | - Graziano Di Carmine
- Department of Chemical, Pharmaceutical and Agricultural Sciences, University of Ferrara, Via L. Borsari, 46, 44121 Ferrara, Italy
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8
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Domcke W, Sobolewski AL. Water Oxidation and Hydrogen Evolution with Organic Photooxidants: A Theoretical Perspective. J Phys Chem B 2022; 126:2777-2788. [PMID: 35385277 DOI: 10.1021/acs.jpcb.2c00705] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
In this Perspective, we discuss a novel water-splitting scenario, namely the direct oxidation of water molecules by organic photooxidants in hydrogen-bonded chromophore-water complexes. In comparison with the established scenario of semiconductor-based water splitting, the distance of electron transfer processes is thereby reduced from mesoscopic scales to the Ångström scale, and the time scale is reduced from milliseconds to femtoseconds, which suppresses competing loss processes. The concept is illustrated by computational studies for the heptazine-H2O complex. The excited-state landscape of this complex has been characterized with ab initio electronic-structure methods and the proton-coupled electron-transfer dynamics has been explored with nonadiabatic dynamics simulations. A unique feature of the heptazine chromophore is the existence of a low-lying and exceptionally long-lived 1ππ* state in which a substantial part of the photon energy can be stored for hundreds of nanoseconds and is available for the oxidation of water molecules. The calculations reveal that the absorption spectra and the photochemical functionalities of heptazine chromophores can be systematically tailored by chemical substitution. The options of harvesting hydrogen and the problems posed by the high reactivity of OH radicals are discussed.
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Affiliation(s)
- Wolfgang Domcke
- Department of Chemistry, Technical University of Munich, D-85747 Garching, Germany
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