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Xu F, Su H, van der Tol JJB, Jansen SAH, Fu Y, Lavarda G, Vantomme G, Meskers S, Meijer EW. Supramolecular Polymerization as a Tool to Reveal the Magnetic Transition Dipole Moment of Heptazines. J Am Chem Soc 2024; 146:15843-15849. [PMID: 38815616 PMCID: PMC11177250 DOI: 10.1021/jacs.4c02174] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2024] [Revised: 05/15/2024] [Accepted: 05/16/2024] [Indexed: 06/01/2024]
Abstract
Heptazine derivatives have attracted significant interest due to their small S1-T1 gap, which contributes to their unique electronic and optical properties. However, the nature of the lowest excited state remains ambiguous. In the present study, we characterize the lowest optical transition of heptazine by its magnetic transition dipole moment. To measure the magnetic transition dipole moment, the flat heptazine must be chiroptically active, which is difficult to achieve for single heptazine molecules. Therefore, we used supramolecular polymerization as an approach to make homochiral stacks of heptazine derivatives. Upon formation of the supramolecular polymers, the preferred helical stacking of heptazine introduces circular polarization of absorption and fluorescence. The magnetic transition dipole moments for the S1 ← S0 and S1 → S0 are determined to be 0.35 and 0.36 Bohr magneton, respectively. These high values of magnetic transition dipole moments support the intramolecular charge transfer nature of the lowest excited state from nitrogen to carbon in heptazine and further confirm the degeneracy of S1 and T1.
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Affiliation(s)
- Fan Xu
- Institute
for Complex Molecular Systems and Laboratory of Macromolecular and
Organic Chemistry, Eindhoven University
of Technology, Eindhoven 5600 MB, Netherlands
| | - Hao Su
- Institute
for Complex Molecular Systems and Laboratory of Macromolecular and
Organic Chemistry, Eindhoven University
of Technology, Eindhoven 5600 MB, Netherlands
- College
of Polymer Science and Engineering and State Key Laboratory of Polymer
Materials Engineering, Sichuan University, Chengdu 610065, China
| | - Joost J. B. van der Tol
- Institute
for Complex Molecular Systems and Laboratory of Macromolecular and
Organic Chemistry, Eindhoven University
of Technology, Eindhoven 5600 MB, Netherlands
| | - Stef A. H. Jansen
- Institute
for Complex Molecular Systems and Laboratory of Macromolecular and
Organic Chemistry, Eindhoven University
of Technology, Eindhoven 5600 MB, Netherlands
| | - Youxin Fu
- Stratingh
Institute for Chemistry, University of Groningen, Nijenborgh4, Groningen 9747AG, Netherlands
| | - Giulia Lavarda
- Institute
for Complex Molecular Systems and Laboratory of Macromolecular and
Organic Chemistry, Eindhoven University
of Technology, Eindhoven 5600 MB, Netherlands
| | - Ghislaine Vantomme
- Institute
for Complex Molecular Systems and Laboratory of Macromolecular and
Organic Chemistry, Eindhoven University
of Technology, Eindhoven 5600 MB, Netherlands
| | - Stefan Meskers
- Institute
for Complex Molecular Systems and Molecular Materials and Nanosystems, Eindhoven University of Technology, Eindhoven 5600 MB, Netherlands
| | - E. W. Meijer
- Institute
for Complex Molecular Systems and Laboratory of Macromolecular and
Organic Chemistry, Eindhoven University
of Technology, Eindhoven 5600 MB, Netherlands
- School
of Chemistry and RNA Institute, UNSW, Sydney NSW 2052, Australia
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2
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Actis A, Melchionna M, Filippini G, Fornasiero P, Prato M, Chiesa M, Salvadori E. Singlet-Triplet Energy Inversion in Carbon Nitride Photocatalysts. Angew Chem Int Ed Engl 2023; 62:e202313540. [PMID: 37801043 DOI: 10.1002/anie.202313540] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2023] [Revised: 10/05/2023] [Accepted: 10/06/2023] [Indexed: 10/07/2023]
Abstract
Time-resolved EPR (TR-EPR) demonstrates the formation of well-defined spin triplet excitons in carbon nitride. This permits to experimentally probe the extent of the triplet wavefunction which delocalizes over several tri-s-triazine units. Analysis of the temperature dependence of the TR-EPR signal reveals the mobility of the triplet excitons. By employing monochromatic light excitation in the range 430-600 nm, the energy of the spin triplet is estimated to be ≈0.2 eV above the conduction band edge, proving that the triplet exciton lies above the corresponding singlet. Comparison between amorphous and graphitic forms establishes the singlet-triplet inversion as a general feature of carbon nitride materials.
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Affiliation(s)
- Arianna Actis
- Department of Chemistry and NIS Centre, University of Torino, Via Pietro Giuria 7, 10125, Torino, Italy
| | - Michele Melchionna
- Department of Chemical and Pharmaceutical, INSTM UdR, University of Trieste, Via Licio Giorgieri 1, 34127, Trieste, Italy
| | - Giacomo Filippini
- Department of Chemical and Pharmaceutical, INSTM UdR, University of Trieste, Via Licio Giorgieri 1, 34127, Trieste, Italy
| | - Paolo Fornasiero
- Department of Chemical and Pharmaceutical, INSTM UdR, University of Trieste, Via Licio Giorgieri 1, 34127, Trieste, Italy
- ICCOM-CNR URT, Via Licio Giorgieri 1, 34127, Trieste, Italy
| | - Maurizio Prato
- Department of Chemical and Pharmaceutical, INSTM UdR, University of Trieste, Via Licio Giorgieri 1, 34127, Trieste, Italy
- Center for Cooperative Research in Biomaterials (CIC biomaGUNE), Basque Research and Technology Alliance (BRTA), Paseo Miramon 194, 20014, Donostia San Sebastián, Spain
- Basque Fdn Sci, Ikerbasque, 48013, Bilbao, Spain
| | - Mario Chiesa
- Department of Chemistry and NIS Centre, University of Torino, Via Pietro Giuria 7, 10125, Torino, Italy
| | - Enrico Salvadori
- Department of Chemistry and NIS Centre, University of Torino, Via Pietro Giuria 7, 10125, Torino, Italy
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Curtis K, King C, Odoh SO. Novel Triangulenes: Computational Investigations of Energy Thresholds for Photocatalytic Water Splitting. Chemphyschem 2023:e202300556. [PMID: 37718310 DOI: 10.1002/cphc.202300556] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2023] [Revised: 09/15/2023] [Accepted: 09/17/2023] [Indexed: 09/19/2023]
Abstract
Organic materials with Inverted Singlet-Triplet (INVEST) gaps are interesting for their potential use in photocatalytic small molecule transformations such as the entirely solar-driven water splitting reaction. However, only a few INVEST emitters are thermodynamically able to split water requiring a first singlet excited dark state, S1 , above 1.27 or 1.76 eV, and absorption near solar the maximum, 2.57 eV. These requirements and the INVEST character are key for achieving a long-lived photocatalyst for water splitting. The only known INVEST emitters that conform to these criteria are large triangular boron carbon nitrides with unknown synthesis pathways. Using ADC(2), a quantum-mechanical method, we describe three triangulenes. 3 a is a cyano azacyclopenta[cd]phenalene derivative while 3 b and 3 c are cycl[3.3.3]azine derivatives. 3 b has a previously undescribed disulfide bridge. Overall, 3 a fulfills requirements for photocatalytic four-electron reduction of water while the S1 states of 3 b and 3 c are likely slightly low for the two-electron reduction process. By analyzing impacts of ligands, we find that there are guidelines describing how S1 -S5 energies and oscillator strengths, T1 energies, and ΔES1T1 gaps are affected, requiring deep-learning algorithms for which studies will be presented by us in due time. The impact of ground-state geometries, solvation effects, as well as reduced-cost ADC(2) algorithms on our findings are also discussed.
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Affiliation(s)
- Kevin Curtis
- Department of Chemistry, University of Nevada Reno, 1664 N. Virginia Street, Reno, NV, 89557-0216, USA
| | - Corban King
- Department of Chemistry, University of Nevada Reno, 1664 N. Virginia Street, Reno, NV, 89557-0216, USA
| | - Samuel O Odoh
- Department of Chemistry, University of Nevada Reno, 1664 N. Virginia Street, Reno, NV, 89557-0216, USA
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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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5
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Ullah N, Chen S, Zhang R. Excited‐state nonadiabatic dynamics simulations on the heptazine and adenine in a water environment: A mini review. J CHIN CHEM SOC-TAIP 2023. [DOI: 10.1002/jccs.202200445] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Affiliation(s)
- Naeem Ullah
- Department of Physics City University of Hong Kong Kowloon Hong Kong SAR China
- Department of Physics Government Degree College Dara Adam Khel, Higher Education Department Khyber Pakhtunkhwah Pakistan
| | - Shunwei Chen
- Department of Physics City University of Hong Kong Kowloon Hong Kong SAR China
- School of Materials Science and Engineering Qilu University of Technology (Shandong Academy of Sciences) Jinan China
| | - Ruiqin Zhang
- Department of Physics City University of Hong Kong Kowloon Hong Kong SAR China
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Morawski O, Gawryś P, Sadło J, Sobolewski AL. Photochemical Hydrogen Storage with Hexaazatrinaphthylene (HATN). Chemphyschem 2022; 23:e202200077. [PMID: 35377513 DOI: 10.1002/cphc.202200077] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2022] [Revised: 03/14/2022] [Indexed: 11/10/2022]
Abstract
When irradiated with violet light, hexaazatrinaphthylene (HATN) extracts a hydrogen atom from an alcohol forming a long-living hydrogenated species. The kinetic isotope effect for fluorescence decay in deuterated methanol (1.56) indicates that the lowest singlet excited state of the molecule is a precursor for intermolecular hydrogen transfer. The photochemical hydrogenation occurs in several alcohols (methanol, ethanol, isopropanol) but not in water. Hydrogenated HATN can be detected optically by an absorption band at 1.78 eV as well as with EPR and NMR techniques. Mass spectroscopy of photoproducts reveal di-hydrogenated HATN structures along with methoxylated and methylated HATN molecules which are generated through the reaction with methoxy radicals (remnants from alcohol splitting). Experimental findings are consistent with the theoretical results which predicted that for the excited state of the HATN-solvent molecular complex, there exists a barrierless hydrogen transfer from methanol but a barrier for the similar oxidation of water.
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Affiliation(s)
- Olaf Morawski
- Institute of Physics Polish Academy of Sciences: Instytut Fizyki Polskiej Akademii Nauk, Radiation and Spectroscopy, Al. Lotnikow 32/46, 02-668, Warsaw, POLAND
| | - Paweł Gawryś
- Institute of Physics Polish Academy of Sciences: Instytut Fizyki Polskiej Akademii Nauk, Radiation and Spectroscopy, Al. Lotników 32/46, 02-668, Warszawa, POLAND
| | - Jarosław Sadło
- Institute of Nuclear Chemistry and Technology, Spectroscopy, ul. Dorodna 16, 03-195, Warsaw, POLAND
| | - Andrzej L Sobolewski
- Institute of Physics Polish Academy of Sciences: Instytut Fizyki Polskiej Akademii Nauk, Radiation and Spectroscopy, Al. Lotników 32/46, 02-668, Warsaw, POLAND
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Penschke C, Edler von Zander R, Beqiraj A, Zehle A, Jahn N, Neumann R, Saalfrank P. Water on porous, nitrogen-containing layered carbon materials: The performance of computational model chemistries. Phys Chem Chem Phys 2022; 24:14709-14726. [DOI: 10.1039/d2cp00657j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Porous, layered materials containing sp2-hybridized carbon and nitrogen atoms, offer through their tunable properties, a versatile route towards tailormade catalysts for electrochemistry and photochemistry. A key molecule interacting with these...
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8
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Huang X, Domcke W. Ab Initio Nonadiabatic Surface-Hopping Trajectory Simulations of Photocatalytic Water Oxidation and Hydrogen Evolution with the Heptazine Chromophore. J Phys Chem A 2021; 125:9917-9931. [PMID: 34748705 DOI: 10.1021/acs.jpca.1c08291] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
In the past decade, polymeric carbon nitrides consisting of heptazine (Hz) building blocks emerged as highly promising materials for photocatalytic hydrogen evolution from water or sacrificial electron donors with near-ultraviolet light. However, the complexity of these materials and their poor characterization at the atomic level are detrimental to the unraveling of the detailed mechanisms of the reactions leading to hydrogen evolution. Recently, it has been shown that a derivative of the Hz molecule, trianisole-heptazine (TAHz), is a potent photobase, which readily oxidizes various derivatives of phenol and even water by an excited-state proton-coupled electron-transfer (PCET) reaction. Energy profiles along minimum-energy reaction paths and relaxed PCET potential-energy surfaces, which previously were computed with ab initio electronic-structure methods for complexes of Hz and TAHz with protic substrates, led to qualitative insights. To obtain more quantitative insight, reaction dynamics simulations are required. In the present work, the time scales of the electron and proton transfer processes and the branching ratios of competing channels were explored with ab initio on-the-fly quasiclassical surface-hopping trajectory simulations for the hydrogen-bonded Hz-H2O complex. By the analysis of representative trajectories, detailed insight into the interplay of various nonadiabatic electronic transitions, electron transfer, proton transfer, and vibrational energy relaxation is obtained. The HzH radicals which are formed by the photoreduction of Hz can disproportionate to Hz and HzH2 in an exothermic reaction with a low reaction barrier. The time scales and branching ratios of competing channels in H-atom photodetachment from the HzH2 molecule also were explored with ab initio surface-hopping simulations. These results delineate for the first time a quantitatively supported scenario of water oxidation and hydrogen evolution with a molecular carbon nitride photocatalyst.
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Affiliation(s)
- Xiang Huang
- Department of Chemistry, Technical University of Munich, Garching D-85747, Germany
| | - Wolfgang Domcke
- Department of Chemistry, Technical University of Munich, Garching D-85747, Germany
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Omist A, Ricci G, Derradji A, Pérez-Jiménez AJ, San-Fabián E, Olivier Y, Sancho-García JC. peri-Acenoacene molecules: tuning of the singlet and triplet excitation energies by modifying their radical character. Phys Chem Chem Phys 2021; 23:24016-24028. [PMID: 34664570 DOI: 10.1039/d1cp03232a] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The energy difference between singlet and triplet excitons, or ΔEST, is a key parameter for novel light-emission mechanisms (i.e., TADF or thermally activated delayed fluorescence) or other photoactivated processes. We have studied a set of conjugated molecules (peri-acenoacenes and their heteroatom-doped analogues) to observe the evolution of their excited-state properties upon increasing the system size with and without substitution with a pair of N atoms. Since these molecules exhibit a (ground-state) diradicaloid character, together with marked correlation effects influencing the excited-states formed, we have applied a variety of theoretical methods (FT-DFT, TD-DFT, SF-TD-DFT, CIS, CIS(D), SCS-CC2, SA-CASSCF, and SC-NEVPT2) to bracket the accuracy of the results while concomitantly providing insights into electronic structure. The results show how this chemical strategy (N-doping) largely modifies not only the excited-state energies but also the oscillator strengths and the ΔEST values, constituting versatile platforms for fine-tuned photophysical applications.
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Affiliation(s)
- A Omist
- Department of Physical Chemistry, University of Alicante, E-03080 Alicante, Spain.
| | - G Ricci
- Unité de Chimie Physique Théorique et Structurale & Laboratoire de Physique du Solid, Namur Institute of Structured Matter, Université de Namur, B-5000 Namur, Belgium
| | - A Derradji
- Department of Physical Chemistry, University of Alicante, E-03080 Alicante, Spain.
| | - A J Pérez-Jiménez
- Department of Physical Chemistry, University of Alicante, E-03080 Alicante, Spain.
| | - E San-Fabián
- Department of Physical Chemistry, University of Alicante, E-03080 Alicante, Spain.
| | - Y Olivier
- Unité de Chimie Physique Théorique et Structurale & Laboratoire de Physique du Solid, Namur Institute of Structured Matter, Université de Namur, B-5000 Namur, Belgium
| | - J C Sancho-García
- Department of Physical Chemistry, University of Alicante, E-03080 Alicante, Spain.
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Hwang D, Schlenker CW. Photochemistry of carbon nitrides and heptazine derivatives. Chem Commun (Camb) 2021; 57:9330-9353. [PMID: 34528956 DOI: 10.1039/d1cc02745j] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We explore the photochemistry of polymeric carbon nitride (C3N4), an archetypal organic photocatalyst, and derivatives of its structural monomer unit, heptazine (Hz). Through spectroscopic studies and computational analysis, we have observed that Hz derivatives can engage in non-innocent hydrogen bonding interactions with hydroxylic species. The photochemistry of these complexes is influenced by intermolecular nπ*/ππ* mixing of non-bonding orbitals of each component and the relative energy of intermolecular charge-transfer (CT) states. Coupling of the former to the latter appears to facilitate proton-coupled electron transfer (PCET), resulting in biradical products. We have also observed that Hz derivatives exhibit an extremely rare inverted singlet/triplet energy splitting (ΔEST). In violation of Hund's multiplicity rules, the lowest energy singlet (S1) is stabilized relative to the lowest triplet (T1) electronic excited state. Exploiting this unique inverted ΔEST character has obvious implications for transformational discoveries in solid-state OLED lighting and photovoltaics. Harnessing this inverted ΔEST, paired with light-driven intermolecular PCET reactions, may enable molecular transformations relevant for applications ranging from solar energy storage to new classes of non-triplet photoredox catalysts for pharmaceutical development. To this end, we have explored the possibility of optically controlling the photochemistry of Hz derivatives using ultrafast pump-push-probe spectroscopy. In this case, the excited state branching ratios among locally excited states of the chromophore and the reactive intermolecular CT state can be manipulated with an appropriate secondary "push" excitation pulse. These results indicate that we can predictively redirect chemical reactivity with light in this system, which is an avidly sought achievement in the field of photochemistry. Looking forward, we anticipate future opportunities for controlling heptazine photochemistry, including manipulating PCET reactivity with a diverse array of substrates and optically delivering reducing equivalents with, for example, water as a partial source of electrons and protons. Furthermore, we wholly expect that, over the next decade, materials such as Hz derivatives, that exhibit inverted ΔEST character, will spawn a significant new research effort in the field of thin-film optoelectronics, where controlling recombination via triplet excitonic states can play a critical role in determining device performance.
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Affiliation(s)
- Doyk Hwang
- Department of Chemistry, University of Washington, Seattle, Washington 98195, USA
| | - Cody W Schlenker
- Department of Chemistry, University of Washington, Seattle, Washington 98195, USA.,Molecular Engineering & Sciences Institute, University of Washington, Seattle, Washington 98195-1652, USA.,Clean Energy Institute, University of Washington, Seattle, Washington 98195-1653, USA.
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Jankowska J, Sobolewski AL. Modern Theoretical Approaches to Modeling the Excited-State Intramolecular Proton Transfer: An Overview. Molecules 2021; 26:molecules26175140. [PMID: 34500574 PMCID: PMC8434569 DOI: 10.3390/molecules26175140] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2021] [Revised: 08/20/2021] [Accepted: 08/23/2021] [Indexed: 02/02/2023] Open
Abstract
The excited-state intramolecular proton transfer (ESIPT) phenomenon is nowadays widely acknowledged to play a crucial role in many photobiological and photochemical processes. It is an extremely fast transformation, often taking place at sub-100 fs timescales. While its experimental characterization can be highly challenging, a rich manifold of theoretical approaches at different levels is nowadays available to support and guide experimental investigations. In this perspective, we summarize the state-of-the-art quantum-chemical methods, as well as molecular- and quantum-dynamics tools successfully applied in ESIPT process studies, focusing on a critical comparison of their specific properties.
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Affiliation(s)
- Joanna Jankowska
- Faculty of Chemistry, University of Warsaw, 02-093 Warsaw, Poland
- Correspondence:
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Pios S, Huang X, Sobolewski AL, Domcke W. Triangular boron carbon nitrides: an unexplored family of chromophores with unique properties for photocatalysis and optoelectronics. Phys Chem Chem Phys 2021; 23:12968-12975. [PMID: 34059871 DOI: 10.1039/d1cp02026a] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
It has recently been shown that cycl[3.3.3]azine and heptazine (1,3,4,6,7,9,9b-heptaazaphenalene) as well as related azaphenalenes exhibit inverted singlet and triplet states, that is, the energy of the lowest singlet excited state (S1) is below the energy of the lowest triplet excited state (T1). This feature is unique among all known aromatic chromophores and is of outstanding relevance for applications in photocatalysis and organic optoelectronics. Heptazine is the building block of the polymeric material graphitic carbon nitride which is an extensively explored photocatalyst in hydrogen evolution photocatalysis. Derivatives of heptazine have also been identified as efficient emitters in organic light emitting diodes (OLEDs). In both areas, the inverted singlet-triplet gap of heptazine is a highly beneficial feature. In photocatalysis, the absence of a long-lived triplet state eliminates the activation of atmospheric oxygen, which is favourable for long-term operational stability. In optoelectronics, singlet-triplet inversion implies the possibility of 100% fluorescence efficiency of electron-hole recombination. However, the absorption and luminescence wavelengths of heptazine and the S1-S0 transition dipole moment are difficult to tune for optimal functionality. In this work, we employed high-level ab initio electronic structure theory to devise and characterize a large family of novel heteroaromatic chromophores, the triangular boron carbon nitrides. These novel heterocycles inherit essential spectroscopic features from heptazine, in particular the inverted singlet-triplet gap, while their absorption and luminescence spectra and transition dipole moments are widely tuneable. For applications in photocatalysis, the wavelength of the absorption maximum can be tuned to improve the overlap with the solar spectrum at the surface of earth. For applications in OLEDs, the colour of emission can be adjusted and the fluorescence yield can be enhanced.
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Affiliation(s)
- Sebastian Pios
- Department of Chemistry, Technical University of Munich, 85747 Garching, Germany.
| | - Xiang Huang
- Department of Chemistry, Technical University of Munich, 85747 Garching, Germany.
| | | | - Wolfgang Domcke
- Department of Chemistry, Technical University of Munich, 85747 Garching, Germany.
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