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Pradhan E, Zeng T. The Lack of Triplet Fusion for an Intramolecular Singlet Fission Chromophore: The Expected, the Unexpected, and a Reconciliation. J Phys Chem Lett 2024; 15:43-50. [PMID: 38127796 DOI: 10.1021/acs.jpclett.3c03238] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2023]
Abstract
Singlet fission (SF) has the potential to play a key role in photovoltaics since it generates a larger number of longer-lived triplet excitons after photoabsorption. Intramolecular SF (iSF) is of special interest since it enables tuning of SF efficiency by adjusting interchromophore configuration through covalent interaction. However, as elaborated in the present work, iSF chromophores are doomed to dissatisfy one general thermodynamic criterion for all SF chromophores, intramolecular or not: E(T2) ≥ 2E(T1), and therefore, the fusion of two triplet excitons to one triplet exciton is thermodynamically favorable. In our nonadiabatic quantum dynamics simulation for a model iSF chromophore, this expected fusion does not occur, because of the inefficient intersystem crossing hidden under the cover of internal conversion of the triplet fusion. A reconciliation is achieved between the dissatisfaction of E(T2) ≥ 2E(T1) and the large tetraradical character for general iSF chromophores.
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Affiliation(s)
- Ekadashi Pradhan
- Department of Chemistry, York University, Toronto, Ontario M3J1P3, Canada
| | - Tao Zeng
- Department of Chemistry, York University, Toronto, Ontario M3J1P3, Canada
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2
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Pradhan E, Zeng T. Triplet Separation after the Fastest Intramolecular Singlet Fission in the Smallest Chromophore. J Chem Theory Comput 2023; 19:2092-2101. [PMID: 36966419 DOI: 10.1021/acs.jctc.3c00096] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/27/2023]
Abstract
Singlet fission is of key importance in harvesting solar energy in solar cells, as it generates a pair of triplet excitons on the incidence of a photon. This phenomenon is not yet widely employed in the organic photovoltaics industry mostly because of the rarity of singlet fission chromophores. Pyrazino[2,3-g]quinoxaline-1,4,6,9-tetraoxide was recently designed as the smallest intramolecular singlet fission chromophore, and it undergoes the fastest singlet fission with a 16 fs time scale. The subsequent separation of the generated triplet-pair is of likewise importance as their efficient generation. Through quantum chemistry calculations and quantum dynamics simulations, we show that the triplet-pair separates to residing on two chromophores with an ∼80% probability on each collision between a chromophore with the triplet-pair and a ground state chromophore. Avoided crossing, instead of conical intersection, is involved in the efficient exciton separation.
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Affiliation(s)
- Ekadashi Pradhan
- Department of Chemistry, York University, Toronto, Ontario M3J1P3, Canada
| | - Tao Zeng
- Department of Chemistry, York University, Toronto, Ontario M3J1P3, Canada
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Pradhan E, Zeng T. Design of the Smallest Intramolecular Singlet Fission Chromophore with the Fastest Singlet Fission. J Phys Chem Lett 2022; 13:11076-11085. [PMID: 36417555 DOI: 10.1021/acs.jpclett.2c03131] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
We designed an intramolecular singlet fission (iSF) chromophore, pyrazino[2,3-g]quinoxaline-1,4,6,9-tetraoxide. Appropriate substitutions into anthracene enhance the tetraradical character, so that the molecule accommodates a pair of triplet excitons in its lowest singlet excited state. Our simulation showed a 16 fs fast iSF of the design, which is a new record. The design also sets a new record of small size iSF chromophore and high exciton density. The design can be synthesized by oxidizing the tertiary N centers of the existent pyrazino[2,3-g]quinoxaline.
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Affiliation(s)
- Ekadashi Pradhan
- Department of Chemistry, York University, Toronto, Ontario M3J1P3, Canada
| | - Tao Zeng
- Department of Chemistry, York University, Toronto, Ontario M3J1P3, Canada
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Zhang Y, Li W, Jiang R, Zhang L, Li Y, Xu X, Liu X. Synthetic Doping of Acenaphthylene through BN/CC Isosterism and a Direct Comparison with BN-Acenaphthene. J Org Chem 2022; 87:12986-12996. [PMID: 36149831 DOI: 10.1021/acs.joc.2c01534] [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
Boron/nitrogen-doped acenaphthylenes, a new class of BN-doped cyclopenta-fused polycyclic aromatic hydrocarbons, were synthesized via indole-directed C-H borylation. The reference molecule BN-acenaphthene was also synthesized in a similar manner. Both BN-acenaphthylene and BN-acenaphthene were unequivocally characterized by single-crystal X-ray analysis. The aromaticities of each ring in BN-acenaphthylenes were quantified by experimental and theoretical methods. Moreover, doping the BN unit into acenaphthylene can increase the LUMO level and decrease the HOMO level, resulting in wider HOMO-LUMO energy gaps. Furthermore, regioselective bromination of BN-acenaphthylene (B-Mes) afforded monobrominated BN-acenaphthylene in good yield. Subsequently, cross-coupling of brominated BN-acenaphthylene gave a series of BN-acenaphthylene derivatives. In addition, the photophysical properties of these BN-acenaphthylene derivatives can be fine-tuned by the substituents on the BN-acenaphthylene scaffold.
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Affiliation(s)
- Yanli Zhang
- School of Chemistry and Chemical Engineering, Tianjin University of Technology, Tianjin 300384, People's Republic of China
| | - Wenlong Li
- School of Chemistry and Chemical Engineering, Tianjin University of Technology, Tianjin 300384, People's Republic of China
| | - Ruijun Jiang
- School of Chemistry and Chemical Engineering, Tianjin University of Technology, Tianjin 300384, People's Republic of China
| | - Lei Zhang
- School of Science, Tianjin Chengjian University, Tianjin 300384, People's Republic of China
| | - Yuanhao Li
- School of Chemistry and Chemical Engineering, Tianjin University of Technology, Tianjin 300384, People's Republic of China
| | - Xiaoyang Xu
- School of Chemistry and Chemical Engineering, Tianjin University of Technology, Tianjin 300384, People's Republic of China
| | - Xuguang Liu
- School of Chemistry and Chemical Engineering, Tianjin University of Technology, Tianjin 300384, People's Republic of China.,State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, People's Republic of China
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Roseiro P, Robert V. Environmental effects on the singlet fission phenomenon: a model Hamiltonian-based study. Phys Chem Chem Phys 2022; 24:15945-15950. [PMID: 35730339 DOI: 10.1039/d2cp01632j] [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
In the screening of compounds for singlet fission, the relative energies of the constitutive units are decisive to fulfil the thermodynamic rules. From a model Hamiltonian constructed on the local spin states of an active chromophore and its environment, it is suggested that embedding greatly influences the energy differences of the active monomer spin states. Even in the absence of charge transfer, the field generated by a singlet environment produces an increase of the [E(S1) - E(S0)]/[E(T1) - E(S0)] critical ratio by up to 6% as compared to the one of a free chromophore. Besides, variations are observed when the intimate electronic structure of the singlet environment is modified. This propensity towards singlet fission is even more pronounced (10%) when the environment is switched to the triplet state. Finally, the embedding is likely to reverse the spin state ordering in the limit of vanishing atomic orbital overlaps. Despite its simplicity, the model stresses the importance of the environment spin nature in the quest for singlet fission candidates, and more generally in spectroscopy analysis.
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Affiliation(s)
- Pablo Roseiro
- Laboratoire de Chimie Quantique, UMR 7177 Université de Strasbourg CNRS, 4 rue Blaise Pascal, 67000, Strasbourg, France.
| | - Vincent Robert
- Laboratoire de Chimie Quantique, UMR 7177 Université de Strasbourg CNRS, 4 rue Blaise Pascal, 67000, Strasbourg, France.
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James D, Pradhan E, Lee S, Choi CH, Zeng T. Dicarbonyl anthracenes and phenanthrenes as singlet fission chromophores. CAN J CHEM 2022. [DOI: 10.1139/cjc-2021-0241] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Singlet fission is a highly desired process in photovoltaic devices as it can significantly enhance photoelectric conversion efficiency. Exploitation of this process in photovoltaics is hindered by the lack of appropriate chromophores. We used mixed-reference spin-flipping time-dependent density functional theory to investigate five di-carbonyl anthracenes and phenanthrenes, with the purpose to design singlet fission chromophores. Two molecules were found to be promising candidates. For all the dicarbonyl molecules, the oxygen lone pair orbitals were found to be involved in the excited states that are relevant to singlet fission.
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Affiliation(s)
- Dylan James
- York University, 7991, Department of Chemistry, Toronto, Ontario, Canada
| | - Ekadashi Pradhan
- York University, 7991, Department of Chemistry, Toronto, Ontario, Canada
| | - Seunghoon Lee
- California Institute of Technology, 6469, Division of Chemistry and Chemical Engineering, Pasadena, California, United States
| | - Cheol Ho Choi
- Kyungpook National University, 34986, Department of Chemistry, Daegu, Daegu, Korea (the Republic of)
| | - Tao Zeng
- York University, 7991, Department of Chemistry, Toronto, Canada, M3J 1P3
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James D, Pradhan E, Zeng T. Design of singlet fission chromophores by the introduction of N-oxyl fragments. J Chem Phys 2022; 156:034303. [DOI: 10.1063/5.0077010] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Dylan James
- Department of Chemistry, York University, Toronto, Ontario M3J1P3, Canada
| | - Ekadashi Pradhan
- Department of Chemistry, York University, Toronto, Ontario M3J1P3, Canada
| | - Tao Zeng
- Department of Chemistry, York University, Toronto, Ontario M3J1P3, Canada
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Singlet/Triplet State Anti/Aromaticity of CyclopentadienylCation: Sensitivity to Substituent Effect. CHEMISTRY 2021. [DOI: 10.3390/chemistry3030055] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
It is well known that singlet state aromaticity is quite insensitive to substituent effects, in the case of monosubstitution. In this work, we use density functional theory (DFT) calculations to examine the sensitivity of triplet state aromaticity to substituent effects. For this purpose, we chose the singlet state antiaromatic cyclopentadienyl cation, antiaromaticity of which reverses to triplet state aromaticity, conforming to Baird’s rule. The extent of (anti)aromaticity was evaluated by using structural (HOMA), magnetic (NICS), energetic (ISE), and electronic (EDDBp) criteria. We find that the extent of triplet state aromaticity of monosubstituted cyclopentadienyl cations is weaker than the singlet state aromaticity of benzene and is, thus, slightly more sensitive to substituent effects. As an addition to the existing literature data, we also discuss substituent effects on singlet state antiaromaticity of cyclopentadienyl cation.
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Baranac-Stojanović M, Stojanović M, Aleksić J. Triplet state (anti)aromaticity of some monoheterocyclic analogues of benzene, naphthalene and anthracene. NEW J CHEM 2021. [DOI: 10.1039/d1nj00207d] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
By employing DFT calculations, we show the influence of heteroatom substitution on the triplet state (anti)aromaticity of benzene, naphthalene and anthracene.
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Affiliation(s)
| | - Milovan Stojanović
- University of Belgrade – Institute of Chemistry
- Technology and Metallurgy – Center for Chemistry
- Belgrade
- Serbia
| | - Jovana Aleksić
- University of Belgrade – Institute of Chemistry
- Technology and Metallurgy – Center for Chemistry
- Belgrade
- Serbia
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Pradhan E, Lee S, Choi CH, Zeng T. Diboron- and Diaza-Doped Anthracenes and Phenanthrenes: Their Electronic Structures for Being Singlet Fission Chromophores. J Phys Chem A 2020; 124:8159-8172. [PMID: 32902270 DOI: 10.1021/acs.jpca.0c06915] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
We used quantum chemistry methods at the levels of mixed-reference spin-flip time-dependent density functional theory and multireference perturbation theory to study diboron- and diaza-doped anthracenes and phenanthrenes. This class of structures recently surged as potential singlet fission chromophores. We studied electronic structures of their excited states and clarified the reasons why they satisfy or fail to satisfy the energy criteria for singlet fission chromophores. Many studied structures have their S1 states not dominated by HOMO → LUMO excitation, so they cannot be described using the conventional two site model. This is attributed to frontier orbital energy shifts induced by the doping and different charge-transfer energies in different one-electron singlet excitations or, in other words, different polarizations of hole and/or particle orbitals in their S1 and T1 states. There is a mirror relation between the orbital energy shifts induced by diboron- and diaza-dopings, which together with alternant hydrocarbon pairings of occupied and unoccupied orbitals, leads to more mirror relations between the excited states of the two types of doped structures.
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Affiliation(s)
- Ekadashi Pradhan
- Department of Chemistry, York University, Toronto, Ontario M3J1P3, Canada
| | - Seunghoon Lee
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
| | - Cheol Ho Choi
- Department of Chemistry, Kyungpook National University, Daegu 702-701, South Korea
| | - Tao Zeng
- Department of Chemistry, York University, Toronto, Ontario M3J1P3, Canada
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Pradhan E, Bentley JN, Caputo CB, Zeng T. Designs of Singlet Fission Chromophores with a Diazadiborinine Framework**. CHEMPHOTOCHEM 2020. [DOI: 10.1002/cptc.202000081] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Affiliation(s)
- Ekadashi Pradhan
- Department of Chemistry York University Toronto Ontario M3 J 1P3 Canada
| | - Jordan N. Bentley
- Department of Chemistry York University Toronto Ontario M3 J 1P3 Canada
| | | | - Tao Zeng
- Department of Chemistry York University Toronto Ontario M3 J 1P3 Canada
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Dobrowolski JC, Karpińska G. Substituent Effect in the First Excited Triplet State of Monosubstituted Benzenes. ACS OMEGA 2020; 5:9477-9490. [PMID: 32363300 PMCID: PMC7191863 DOI: 10.1021/acsomega.0c00712] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/18/2020] [Accepted: 03/16/2020] [Indexed: 05/08/2023]
Abstract
The structure of 30 monosubstituted benzenes in the first excited triplet T1 state was optimized with both unrestricted (U) and restricted open shell (RO) approximations combined with the ωB97XD/aug-cc-pVTZ basis method. The substituents exhibited diverse σ- and π-electron-donating and/or -withdrawing groups. Two different positions of the substituents are observed in the studied compounds in the T1 state: one distorted from the plane and the other coplanar with a quinoidal ring. The majority of the substituents are π-electron donating in the first group while π-electron withdrawing in the second one. Basically, U- and RO-ωB97XD approximations yield concordant results except for the B-substituents and a few of the planar groups. In the T1 state, the studied molecules are not aromatic, yet aromaticity estimated using the HOMA (harmonic oscillator model of aromaticity) index increases from ca. -0.2 to ca. 0.4 with substituent distortion, while in the S1 state, they are only slightly less aromatic than in the ground state (HOMA ≈0.8 vs ≈1.0, respectively). Unexpectedly, the sEDA(T1) and pEDA(T1) substituent effect descriptors do not correlate with analogous parameters for the ground and first excited singlet states. This is because in the T1 state, the geometry of the ring changes dramatically and the sEDA(T1) and pEDA(T1) descriptors do not characterize only the functional group but the entire molecule. Thus, they cannot provide useful scales for the substituents in the T1 states. We found that the spin density in the T1 states is accumulated at the Cipso and Cp atoms, and with the substituent deformation angle, it nonlinearly increases at the former while decreases at the latter. It appeared that the gap between singly unoccupied molecular orbital and singly occupied molecular orbital (SUMO-SOMO) is determined by the change of the SOMO energy because the former is essentially constant. For the nonplanar structures, SOMO correlates with the torsion angle of the substituent and the ground-state pEDA(S0) descriptor of the π-electron-donating substituents ranging from 0.02 to 0.2 e. Finally, shapes of the SOMO-1 instead of SOMO frontier orbitals in the T1 state somehow resemble the highest occupied molecular orbital ones of the S0 and S1 states. For several planar systems, the shape of the U- and RO-density functional theory-calculated SOMO-1 orbitals differs substantially.
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Abstract
Density functional theory calculations have been performed to explore the substituent effect on benzene's structure and aromaticity upon excitation to the first triplet excited state (T1). Discussion is based on spin density analysis, HOMA (harmonic oscillator model of aromaticity), NICS (nucleus-independent chemical shift), ACID (anisotropy of the induced current density), and monohydrogenation free energies and shows that a large span of aromatic properties, from highly antiaromatic to strongly aromatic, could be achieved by varying the substituent. This opens up a possibility of controlling benzene's physicochemical behavior in its excited state, while molecular motion, predicted for several derivatives, could be of interest for the development of photomechanical materials.
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Affiliation(s)
- Marija Baranac-Stojanović
- Faculty of Chemistry, University of Belgrade, Studentski trg 12-16, P.O. Box 158, Belgrade 11000, Serbia
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