1
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Duszka MW, Rode MF, Sobolewski AL. Computational design of boron-free triangular molecules with inverted singlet-triplet energy gap. Phys Chem Chem Phys 2024; 26:19130-19137. [PMID: 38973243 DOI: 10.1039/d4cp01658k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/09/2024]
Abstract
A novel, computationally designed, class of triangular-shape organic molecules with an inverted singlet-triplet (IST) energy gap is investigated with ab initio electronic structure methods. The considered molecular systems are cyclic oligomers and their common feature is electronic conjugation along the molecular rim. Vertical excitation energies from the electronic ground state to the lowest singlet and triplet excited states were computed, as well as vertical emission energies from these states to the ground state. The results underscore the significance of optimizing excited-state geometries to accurately describe the optoelectronic properties of IST molecules, in particular with respect to their application in OLEDs.
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Affiliation(s)
| | - Michał F Rode
- Institute of Physics, Polish Academy of Sciences, Warsaw, Poland.
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2
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Wilson KD, Styers WH, Wood SA, Woods RC, McMahon RJ, Liu Z, Yang Y, Garand E. Spectroscopic Quantification of the Inverted Singlet-Triplet Gap in Pentaazaphenalene. J Am Chem Soc 2024; 146:15688-15692. [PMID: 38815061 DOI: 10.1021/jacs.4c05043] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/01/2024]
Abstract
We report the direct and accurate spectroscopic quantification of the inverted singlet-triplet gap in 1,3,4,6,9b-pentaazaphenalene. This measurement is achieved by directly probing the lowest singlet and triplet states via high-resolution cryogenic anion photoelectron spectroscopy. The assignment of the first excited singlet state is confirmed by visible absorption spectroscopy in an argon matrix at 20 K. Our measurements yield an inverted singlet-triplet gap with ΔEST= -0.047(7) eV. The accurate quantification of the singlet-triplet gap presented here allows for direct evaluation of various computational electronic structure methods and highlights the critical importance of the proper description of the double excitation character of these electronic states. Overall, this study validates the idea that despite Hund's multiplicity rule, useful organic chromophores can have inherently inverted singlet-triplet gaps.
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Affiliation(s)
- Kenneth D Wilson
- Department of Chemistry, University of Wisconsin─Madison, Madison, Wisconsin 53706, United States
| | - William H Styers
- Department of Chemistry, University of Wisconsin─Madison, Madison, Wisconsin 53706, United States
| | - Samuel A Wood
- Department of Chemistry, University of Wisconsin─Madison, Madison, Wisconsin 53706, United States
| | - R Claude Woods
- Department of Chemistry, University of Wisconsin─Madison, Madison, Wisconsin 53706, United States
| | - Robert J McMahon
- Department of Chemistry, University of Wisconsin─Madison, Madison, Wisconsin 53706, United States
| | - Zhe Liu
- Department of Chemistry, University of Wisconsin─Madison, Madison, Wisconsin 53706, United States
| | - Yang Yang
- Department of Chemistry, University of Wisconsin─Madison, Madison, Wisconsin 53706, United States
| | - Etienne Garand
- Department of Chemistry, University of Wisconsin─Madison, Madison, Wisconsin 53706, United States
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3
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Manna AK. Thiocarbonyl-Bridged N-Heterotriangulenes for Energy Efficient Triplet Photosensitization: A Theoretical Perspective. Chemphyschem 2024:e202400371. [PMID: 38700483 DOI: 10.1002/cphc.202400371] [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: 03/31/2024] [Revised: 05/02/2024] [Accepted: 05/03/2024] [Indexed: 05/05/2024]
Abstract
Structurally-rigid metal-free organic molecules are of high demand for various triplet harvesting applications. However, inefficient intersystem crossing (ISC) due to large singlet-triplet gap (Δ E S - T ${\Delta {E}_{S-T}}$ ) and small spin-orbit coupling (SOC) between lowest excited singlet and triplet often limits their efficiency. Excited electronic states, fluorescence and ISC rates in several thiocarbonyl-bridged N-heterotriangulene ( m ${m}$ S-HTG) with systematically increased thione content (m = ${m=}$ 0-3) are investigated implementing polarization consistent time-dependent optimally-tuned range-separated hybrid. All m ${m}$ S-HTGs are dynamically stable and also thermodynamically feasible to synthesize. Relative energies of several low-lying singlets (S n ${{S}_{n}}$ ) and triplets (T n ${{T}_{n}}$ ), and their excitation nature (i. e.,n π * ${n{\pi }^{^{\ast}}}$ orπ π * ${\pi {\pi }^{^{\ast}}}$ ) and SOC are determined for these m ${m}$ S-HTGs in dichloromethane. Low-energy optical peak displays gradual red-shift with increasing thione content due to relatively smaller electronic gap resulted from greater degree of orbital delocalization. Significantly large SOC due to different orbital-symmetry and heavy-atom effect produces remarkably high ISC rates (k I S C ${{k}_{ISC}}$ ~1012 s-1) for enthalpically favouredS 1 n π * → T 2 ${{S}_{1}\left(n{\pi }^{^{\ast}}\right)\to {T}_{2}}$ (π π * ${\pi {\pi }^{^{\ast}}}$ ) channel in these m ${m}$ S-HTGs, which outcompete radiative fluorescence rates (~108 s-1) even directly from higher lying optically brightπ π * ${\pi {\pi }^{^{\ast}}}$ singlets. Importantly, high energy triplet excitons of ~1.7 eV resulting from such significantly large ISC rates from non-fluorescentS 1 n π * ${{S}_{1}\left(n{\pi }^{^{\ast}}\right)}$ make these thiocarbonylated HTGs ideal candidates for energy efficient triplet harvest including triplet-photosensitization.
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Affiliation(s)
- Arun K Manna
- Department of Chemistry, Indian Institute of Technology Tirupati, 517619, Tirupati, Andhra Pradesh, India
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4
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Jorner K, Pollice R, Lavigne C, Aspuru-Guzik A. Ultrafast Computational Screening of Molecules with Inverted Singlet-Triplet Energy Gaps Using the Pariser-Parr-Pople Semiempirical Quantum Chemistry Method. J Phys Chem A 2024; 128:2445-2456. [PMID: 38485448 PMCID: PMC10983003 DOI: 10.1021/acs.jpca.3c06357] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2023] [Revised: 02/23/2024] [Accepted: 02/23/2024] [Indexed: 04/04/2024]
Abstract
Molecules with an inverted energy gap between their first singlet and triplet excited states have promising applications in the next generation of organic light-emitting diode (OLED) materials. Unfortunately, such molecules are rare, and only a handful of examples are currently known. High-throughput virtual screening could assist in finding novel classes of these molecules, but current efforts are hampered by the high computational cost of the required quantum chemical methods. We present a method based on the semiempirical Pariser-Parr-Pople theory augmented by perturbation theory and show that it reproduces inverted gaps at a fraction of the cost of currently employed excited-state calculations. Our study paves the way for ultrahigh-throughput virtual screening and inverse design to accelerate the discovery and development of this new generation of OLED materials.
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Affiliation(s)
- Kjell Jorner
- Institute
of Chemical and Bioengineering, Department of Chemistry and Applied
Biosciences, ETH Zürich, Vladimir-Prelog-Weg 1, Zürich CH-8093, Switzerland
- Department
of Chemistry and Chemical Engineering, Chalmers
University of Technology, Kemigården 4, Gothenburg SE-41258, Sweden
- Chemical
Physics Theory Group, Department of Chemistry, University of Toronto, 80 St. George Street, Toronto M5S 3H6, Canada
- Department
of Computer Science, University of Toronto, 40 St. George Street, Toronto M5S 2E4, Canada
| | - Robert Pollice
- Chemical
Physics Theory Group, Department of Chemistry, University of Toronto, 80 St. George Street, Toronto M5S 3H6, Canada
- Department
of Computer Science, University of Toronto, 40 St. George Street, Toronto M5S 2E4, Canada
- Stratingh
Institute for Chemistry, University of Groningen, Nijenborgh 4, Groningen 9747, AG, The Netherlands
| | - Cyrille Lavigne
- Chemical
Physics Theory Group, Department of Chemistry, University of Toronto, 80 St. George Street, Toronto M5S 3H6, Canada
- Department
of Computer Science, University of Toronto, 40 St. George Street, Toronto M5S 2E4, Canada
| | - Alán Aspuru-Guzik
- Chemical
Physics Theory Group, Department of Chemistry, University of Toronto, 80 St. George Street, Toronto M5S 3H6, Canada
- Department
of Computer Science, University of Toronto, 40 St. George Street, Toronto M5S 2E4, Canada
- Department
of Chemical Engineering & Applied Chemistry, University of Toronto, 200 College Street, Toronto M5S 3E5, Canada
- Department
of Materials Science & Engineering, University of Toronto, 184 College Street, Toronto M5S 3E4, Canada
- Vector
Institute for Artificial Intelligence, 661 University Ave. Suite 710, Toronto M5G 1M1, Canada
- Lebovic
Fellow, Canadian Institute for Advanced
Research (CIFAR), 661
University Avenue, Toronto M5G 1M1, Canada
- Acceleration
Consortium, University of Toronto, 700 University Avenue, Toronto M5G 1Z5, Canada
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5
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Nigam A, Pollice R, Friederich P, Aspuru-Guzik A. Artificial design of organic emitters via a genetic algorithm enhanced by a deep neural network. Chem Sci 2024; 15:2618-2639. [PMID: 38362419 PMCID: PMC10866360 DOI: 10.1039/d3sc05306g] [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: 10/07/2023] [Accepted: 01/10/2024] [Indexed: 02/17/2024] Open
Abstract
The design of molecules requires multi-objective optimizations in high-dimensional chemical space with often conflicting target properties. To navigate this space, classical workflows rely on the domain knowledge and creativity of human experts, which can be the bottleneck in high-throughput approaches. Herein, we present an artificial molecular design workflow relying on a genetic algorithm and a deep neural network to find a new family of organic emitters with inverted singlet-triplet gaps and appreciable fluorescence rates. We combine high-throughput virtual screening and inverse design infused with domain knowledge and artificial intelligence to accelerate molecular generation significantly. This enabled us to explore more than 800 000 potential emitter molecules and find more than 10 000 candidates estimated to have inverted singlet-triplet gaps (INVEST) and appreciable fluorescence rates, many of which likely emit blue light. This class of molecules has the potential to realize a new generation of organic light-emitting diodes.
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Affiliation(s)
- AkshatKumar Nigam
- Chemical Physics Theory Group, Department of Chemistry, University of Toronto 80 St. George St Toronto Ontario M5S 3H6 Canada
- Department of Computer Science, University of Toronto 40 St. George St Toronto Ontario M5S 2E4 Canada
| | - Robert Pollice
- Chemical Physics Theory Group, Department of Chemistry, University of Toronto 80 St. George St Toronto Ontario M5S 3H6 Canada
- Department of Computer Science, University of Toronto 40 St. George St Toronto Ontario M5S 2E4 Canada
| | - Pascal Friederich
- Chemical Physics Theory Group, Department of Chemistry, University of Toronto 80 St. George St Toronto Ontario M5S 3H6 Canada
- Department of Computer Science, University of Toronto 40 St. George St Toronto Ontario M5S 2E4 Canada
- Institute of Nanotechnology, Karlsruhe Institute of Technology Hermann-von-Helmholtz-Platz 1 76344 Eggenstein-Leopoldshafen Germany
- Institute of Theoretical Informatics, Karlsruhe Institute of Technology Am Fasanengarten 5 76131 Karlsruhe Germany
| | - Alán Aspuru-Guzik
- Chemical Physics Theory Group, Department of Chemistry, University of Toronto 80 St. George St Toronto Ontario M5S 3H6 Canada
- Department of Computer Science, University of Toronto 40 St. George St Toronto Ontario M5S 2E4 Canada
- Vector Institute for Artificial Intelligence 661 University Ave Suite 710 Toronto Ontario M5G 1M1 Canada
- Department of Chemical Engineering & Applied Chemistry, University of Toronto 200 College St. Ontario M5S 3E5 Canada
- Department of Materials Science & Engineering, University of Toronto, 184 College St. Ontario M5S 3E4 Canada
- Lebovic Fellow, Canadian Institute for Advanced Research (CIFAR) 661 University Ave Toronto Ontario M5G Canada
- Acceleration Consortium Toronto Ontario M5G 3H6 Canada
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6
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Blasco D, Nasibullin RT, Valiev RR, Monge M, López-de-Luzuriaga JM, Sundholm D. Experimental and computational studies of the optical properties of 2,5,8-tris(phenylthiolato)heptazine with an inverted singlet-triplet gap. Phys Chem Chem Phys 2024; 26:5922-5931. [PMID: 38317631 DOI: 10.1039/d3cp05242g] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2024]
Abstract
Photophysical properties of the three-fold symmetric 2,5,8-tris(phenylthiolato)heptazine molecule (1) are studied from combined experimental and computational viewpoints. The intense blue photoemission of 1 in the solid state and in toluene solution is proposed to have a fluorescent origin on the basis of a relatively short emission lifetime and no detectable triplet decay. Calculations at correlated ab initio levels of theory also show that 1 has a large inverted singlet-triplet (IST) gap, a non-vanishing spin-orbit coupling matrix element between the first excited singlet and triplet states, and a fast intersystem crossing rate constant that leads to singlet population from the higher-lying triplet state. The IST gap implies that the first excited singlet state is the lowest excited one, agreeing with the measured fluorescent behaviour of 1. IST gaps are also obtained for the oxygen-containing (2) and selenium-containing (3) analogues of 1 at the ADC(2) level of theory, but not for the tellurium one (4). Calculations of the magnetically induced current density demonstrate that the heptazine core of 1 is globally non-aromatic due to the alternation of carbon and nitrogen atoms along its external rim.
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Affiliation(s)
- Daniel Blasco
- Departamento de Química, Instituto de Investigación en Química (IQUR), Universidad de La Rioja, Madre de Dios 53, 26006, Logroño, Spain.
| | - Rinat T Nasibullin
- Department of Chemistry, Faculty of Science, University of Helsinki, P. O. Box 55 (A. I. Virtasen aukio 1), FIN-00014, Helsinki, Finland.
| | - Rashid R Valiev
- Department of Chemistry, Faculty of Science, University of Helsinki, P. O. Box 55 (A. I. Virtasen aukio 1), FIN-00014, Helsinki, Finland.
| | - Miguel Monge
- Departamento de Química, Instituto de Investigación en Química (IQUR), Universidad de La Rioja, Madre de Dios 53, 26006, Logroño, Spain.
| | - José M López-de-Luzuriaga
- Departamento de Química, Instituto de Investigación en Química (IQUR), Universidad de La Rioja, Madre de Dios 53, 26006, Logroño, Spain.
| | - Dage Sundholm
- Department of Chemistry, Faculty of Science, University of Helsinki, P. O. Box 55 (A. I. Virtasen aukio 1), FIN-00014, Helsinki, Finland.
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7
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Kim H, Scholes GD, Min SK. Extension of molecules with an inverted singlet-triplet gap with conjugated branches to alter the oscillator strength. Phys Chem Chem Phys 2024; 26:5508-5516. [PMID: 38282516 DOI: 10.1039/d3cp05580a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2024]
Abstract
Molecules that violate Hund's rule and possess negative singlet-triplet gaps (ΔEST) have been actively studied for their potential usage in organic light emitting diodes without the need for thermal activation. However, the weak oscillator strength from the symmetry of such molecules has been recognized as their shortcoming for their application in optoelectronic devices. A group of molecules with a common structural motif involving the original molecule with an inverted gap having branches consisting of conjugated molecules of varied structures and extent of conjugation have been predicted to have desirable oscillator strength, but only few detailed and comprehensive studies regarding the form of excited states and the reason behind the improved oscillator strength have been carried out. We show in this work a series of analyses that suggest that the increase of oscillator strength is correlated with the nature of the excited state changing from a localized excitation to a delocalized excitation involving the central molecule and the branches. The resulting oscillator strength thus depends on the energetic matching of the branching molecule and the central molecule, rather than solely the oscillator strength of the central molecule. From the ΔEST inversion point of view, the static correlation with low-lying doubly excited configurations, the key mechanism behind the inversion in the localized excited state, weakens as the excited states delocalize. As a consequence, the dynamic correlation has a more decisive effect in determining the singlet-triplet gap.
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Affiliation(s)
- Hwon Kim
- Department of Chemistry, Ulsan National Institute of Science and Technology (UNIST), South Korea.
| | - Gregory D Scholes
- Department of Chemistry, Princeton University, Princeton, New Jersey 08544, USA
| | - Seung Kyu Min
- Department of Chemistry, Ulsan National Institute of Science and Technology (UNIST), South Korea.
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8
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Valiev RR, Nasibullin RT, Merzlikin BS, Khoroshkin K, Cherepanov VN, Sundholm D. Internal conversion induced by external electric and magnetic fields. Phys Chem Chem Phys 2024; 26:2945-2950. [PMID: 38205797 DOI: 10.1039/d3cp05409h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2024]
Abstract
We have developed a new methodology for calculating contributions to the rate constants (kIC) of internal conversion that are induced by external electric (kIC-E) or magnetic (kIC-M) fields. The influence of the external electric and magnetic fields on the kIC was estimated for seven representative molecules. We show that the kIC-E contribution calculated at a field strength of 1011 V m-1 is generally as large as the kIC rate constant in the absence of the external field. For indocyanine green, azaoxa[8]circulene, and pyromitene 567, the kIC-E contribution is as large as kIC already at a field strength of 109 V m-1. Such electric-field strengths occur for example in plasmonic studies and in strong laser-field experiments. The induced effect on the kIC rate constant should be accounted for in calculations of photophysical properties of molecules involved in such experiments. The induced effect of an external magnetic field on kIC can be neglected in experiments on Earth because the magnetic contribution becomes significant only at very strong magnetic fields of 104-105 T that cannot be achieved on Earth. However, the magnetic effect on the rate constant of internal conversion can be important in astrophysical studies, where extremely strong magnetic fields occur near neutron stars and white dwarfs.
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Affiliation(s)
- R R Valiev
- Department of Chemistry, Faculty of Science, P.O. Box 55 (A.I. Virtanens plats 1), FIN-00014 University of Helsinki, Helsinki, Finland.
| | | | - B S Merzlikin
- Tomsk State University, 36 Lenin Avenue, Tomsk, Russia
| | - K Khoroshkin
- Tomsk State University, 36 Lenin Avenue, Tomsk, Russia
| | | | - D Sundholm
- Department of Chemistry, Faculty of Science, P.O. Box 55 (A.I. Virtanens plats 1), FIN-00014 University of Helsinki, Helsinki, Finland.
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9
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Pu YJ, Valverde D, Sancho-García JC, Olivier Y. Computational Design of Multiple Resonance-Type BN Molecules for Inverted Singlet and Triplet Excited States. J Phys Chem A 2023; 127:10189-10196. [PMID: 38011598 DOI: 10.1021/acs.jpca.3c06573] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2023]
Abstract
A computational design of linearly extended multiple resonance (MR)-type BN molecules based on DABNA-1 is proposed herein in the quest to find potential candidates that exhibit a negative singlet-triplet gap (ΔEST) and a large oscillator strength value. The impact of a proper account of the electron correlation in the lowest singlet and triplet excited states is systematically investigated by using double-hybrid functionals within the TD-DFT framework, as well as wavefunction-based methods (EOM-CCSD and SCS-CC2), since this contribution plays an essential role in driving the magnitude of the ΔEST in MR-TADF and inverted singlet-triplet gap compounds. Our results point out a gradual reduction of the ΔEST gap with respect to the increasing sum of the number of B and N atoms, reaching negative ΔEST values for some molecules as a function of their size. The double-hybrid functionals reproduce the gap with only slight deviation compared to available experimental data for DABNA-1, ν-DABNA, and mDBCz and nicely agree with high-level quantum mechanical methods (e.g., EOM-CCSD and SCS-CC2). Larger oscillator strengths are found compared to the azaphenalene-type molecules, also exhibiting the inversion of their singlet and triplet excited states. We hope this study can serve as a motivation for further design of the molecules showing negative ΔEST based on boron- and nitrogen-doped polyaromatic hydrocarbons.
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Affiliation(s)
- Yong-Jin Pu
- RIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama 351-0198, Japan
| | - Danillo Valverde
- Laboratory for Computational Modeling of Functional Materials, Namur Institute of Structured Matter, Université de Namur, Rue de Bruxelles, 61, B-5000 Namur, Belgium
| | | | - Yoann Olivier
- Laboratory for Computational Modeling of Functional Materials, Namur Institute of Structured Matter, Université de Namur, Rue de Bruxelles, 61, B-5000 Namur, Belgium
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10
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Loos PF, Lipparini F, Jacquemin D. Heptazine, Cyclazine, and Related Compounds: Chemically-Accurate Estimates of the Inverted Singlet-Triplet Gap. J Phys Chem Lett 2023:11069-11075. [PMID: 38048474 DOI: 10.1021/acs.jpclett.3c03042] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/06/2023]
Abstract
Molecules that violate Hund's rule and exhibit an inverted gap between the lowest singlet S1 and triplet T1 excited states have attracted considerable attention due to their potential applications in optoelectronics. Among these molecules, the triangular-shaped heptazine, and its derivatives, have been in the limelight. However, conflicting reports have arisen regarding the relative energies of S1 and T1. Here, we employ highly accurate levels of theory, such as CC3, to not only resolve the debate concerning the sign but also quantify the magnitude of the S1-T1 gap. We also determined the 0-0 energies to evaluate the significance of the vertical approximation. In addition, we compute reference S1-T1 gaps for a series of 10 related molecules. This enables us to benchmark lower-order methods for future applications in larger systems within the same family of compounds. This contribution can serve as a foundation for the design of triangular-shaped molecules with enhanced photophysical properties.
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Affiliation(s)
- Pierre-François Loos
- Laboratoire de Chimie et Physique Quantiques, Université de Toulouse, CNRS, UPS, 31400 Toulouse, France
| | - Filippo Lipparini
- Dipartimento di Chimica e Chimica Industriale, University of Pisa, Via Moruzzi 3, 56124 Pisa, Italy
| | - Denis Jacquemin
- Nantes Université, CNRS, CEISAM UMR 6230, F-44000 Nantes, France
- Institut Universitaire de France, 75005 Paris, France
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11
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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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12
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Drwal D, Matousek M, Golub P, Tucholska A, Hapka M, Brabec J, Veis L, Pernal K. Role of Spin Polarization and Dynamic Correlation in Singlet-Triplet Gap Inversion of Heptazine Derivatives. J Chem Theory Comput 2023; 19:7606-7616. [PMID: 37864544 PMCID: PMC10653106 DOI: 10.1021/acs.jctc.3c00781] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2023] [Indexed: 10/23/2023]
Abstract
The new generation of proposed light-emitting molecules for organic light-emitting diodes (OLEDs) has raised considerable research interest due to its exceptional feature─a negative singlet-triplet (ST) gap violating Hund's multiplicity rule in the excited S1 and T1 states. We investigate the role of spin polarization in the mechanism of ST gap inversion. Spin polarization is associated with doubly excited determinants of certain types, whose presence in the wave function expansion favors the energy of the singlet state more than that of the triplet. Using a perturbation theory-based model for spin polarization, we propose a simple descriptor for prescreening of candidate molecules with negative ST gaps and prove its usefulness for heptazine-type molecules. Numerical results show that the quantitative effect of spin polarization decreases linearly with the increasing highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) exchange integral. Comparison of single- and multireference coupled-cluster predictions of ST gaps shows that the former methods provide good accuracy by correctly balancing the effects of doubly excited determinants and dynamic correlation. We also show that accurate ST gaps may be obtained using a complete active space model supplemented with dynamic correlation from multireference adiabatic connection theory.
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Affiliation(s)
- Daria Drwal
- Institute
of Physics, Lodz University of Technology, ul. Wolczanska 219, 90-924 Lodz, Poland
| | - Mikulas Matousek
- J.
Heyrovský Institute of Physical Chemistry, Academy of Sciences
of the Czech Republic, v.v.i., Dolejškova 3, 18223 Prague 8, Czech Republic
- Faculty
of Mathematics and Physics, Charles University, 12116 Prague, Czech Republic
| | - Pavlo Golub
- J.
Heyrovský Institute of Physical Chemistry, Academy of Sciences
of the Czech Republic, v.v.i., Dolejškova 3, 18223 Prague 8, Czech Republic
| | - Aleksandra Tucholska
- Institute
of Physics, Lodz University of Technology, ul. Wolczanska 219, 90-924 Lodz, Poland
| | - Michał Hapka
- Faculty
of Chemistry, University of Warsaw, ul. L. Pasteura 1, 02-093 Warsaw, Poland
| | - Jiri Brabec
- J.
Heyrovský Institute of Physical Chemistry, Academy of Sciences
of the Czech Republic, v.v.i., Dolejškova 3, 18223 Prague 8, Czech Republic
| | - Libor Veis
- J.
Heyrovský Institute of Physical Chemistry, Academy of Sciences
of the Czech Republic, v.v.i., Dolejškova 3, 18223 Prague 8, Czech Republic
| | - Katarzyna Pernal
- Institute
of Physics, Lodz University of Technology, ul. Wolczanska 219, 90-924 Lodz, Poland
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13
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Sandoval-Salinas ME, Ricci G, Pérez-Jiménez AJ, Casanova D, Olivier Y, Sancho-García JC. Correlation vs. exchange competition drives the singlet-triplet excited-state inversion in non-alternant hydrocarbons. Phys Chem Chem Phys 2023; 25:26417-26428. [PMID: 37522306 DOI: 10.1039/d3cp02465b] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/01/2023]
Abstract
In this work, we focus on the understanding of the driving force behind the S1-T1 excited-state energy inversion (which would thus violate Hund's rule, making the S1 state lower in energy than the T1 state) of two non-benzenoid non-alternant hydrocarbons, composed of odd-membered rings. The molecules considered here have identical chemical composition but different atomic configuration in space. The delicate interplay between structural and electronic factors that might induce inversion and its energy extension, only by a few meV, is systematically investigated here by state-of-the-art calculations. Qualitative and quantitative accurate predictions are obtained employing post-HF methods, thanks to the balanced and careful inclusion of electron correlation effects. The obtained results might guide and rationalize new searches for molecules violating Hund's rule, concomitantly demonstrating the importance of key contributions from the theoretical method of choice.
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Affiliation(s)
- M E Sandoval-Salinas
- Department of Physical Chemistry, University of Alicante, E-03080 Alicante, Spain.
- School of Physical and Chemical Science, Queen Mary University of London, London, UK
| | - 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 J Pérez-Jiménez
- Department of Physical Chemistry, University of Alicante, E-03080 Alicante, Spain.
| | - D Casanova
- Donostia International Physics Center (DIPC), E-20018 Donostia, Euskadi, Spain.
- IKERBASQUE-Basque Foundation for Science, E-48009 Bilbao, Euskadi, 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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14
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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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15
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Omar Ö, Xie X, Troisi A, Padula D. Identification of Unknown Inverted Singlet-Triplet Cores by High-Throughput Virtual Screening. J Am Chem Soc 2023; 145:19790-19799. [PMID: 37639703 PMCID: PMC10510316 DOI: 10.1021/jacs.3c05452] [Citation(s) in RCA: 10] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2023] [Indexed: 08/31/2023]
Abstract
Molecules where the energy of the lowest excited singlet state is found below the energy of the lowest triplet state (inverted singlet-triplet molecules) are extremely rare. It is particularly challenging to discover new ones through virtual screening because the required wavefunction-based methods are expensive and unsuitable for high-throughput calculations. Here, we devised a virtual screening approach where the molecules to be considered with advanced methods are pre-selected with increasingly more sophisticated filters that include the evaluation of the HOMO-LUMO exchange integral and approximate CASSCF calculations. A final set of 7 candidates (0.05% of the initial 15 000) were verified to possess inversion between singlet and triplet states with state-of-the-art multireference methods (MS-CASPT2). One of them is deemed of particular interest because it is unrelated to other proposals made in the literature.
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Affiliation(s)
- Ömer
H. Omar
- Department
of Chemistry, University of Liverpool, Liverpool L69 7ZD, U.K.
| | - Xiaoyu Xie
- Department
of Chemistry, University of Liverpool, Liverpool L69 7ZD, U.K.
| | - Alessandro Troisi
- Department
of Chemistry, University of Liverpool, Liverpool L69 7ZD, U.K.
| | - Daniele Padula
- Dipartimento
di Biotecnologie, Chimica e Farmacia, Università
di Siena, Via A. Moro
2, Siena 53100, Italy
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16
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Sobolewski AL, Domcke W. Excited-state singlet-triplet inversion in hexagonal aromatic and heteroaromatic compounds. Phys Chem Chem Phys 2023; 25:21875-21882. [PMID: 37566410 DOI: 10.1039/d3cp01666h] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/12/2023]
Abstract
The inversion of the energies of the lowest singlet (S1) and lowest triplet (T1) excited states in violation of Hund's multiplicity rule is a rare phenomenon in stable organic molecules. S1-T1 inversion has significant consequences for the photophysics and photochemistry of organic chromophores. In this work, wave-function based ab initio computational methods were employed to explore the possibility of S1-T1 inversion in hexagonal polycyclic aromatic and heteroaromatic compounds. In these molecules, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) are two-fold degenerate. The HOMO-LUMO transition gives rise to three singlet and three triplet excited states. While the singlet-triplet energy gap ΔST, defined as the energy difference between the S1 state and the T1 state, is clearly positive for benzene, it is predicted to be close to zero for borazine, the boron nitride analogue of benzene. Although ΔST decreases with increasing size of hexagonal polycyclic aromatics, it remains positive up to circumcoronene (19 rings). However, symmetry-preserving substitution of C-C pairs by B-N groups in the interior, keeping the conjugation of the outer rim intact, results in compounds with robustly negative ΔST. These findings establish the existence of a new family of boron carbon nitrides with inverted singlet-triplet gaps.
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Affiliation(s)
| | - Wolfgang Domcke
- Department of Chemistry, Technical University of Munich, D-75747 Garching, Germany.
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17
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Dreuw A, Hoffmann M. The inverted singlet-triplet gap: a vanishing myth? Front Chem 2023; 11:1239604. [PMID: 37577065 PMCID: PMC10413108 DOI: 10.3389/fchem.2023.1239604] [Citation(s) in RCA: 11] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2023] [Accepted: 07/12/2023] [Indexed: 08/15/2023] Open
Abstract
Molecules with an inverted singlet-triplet gap (STG) between the first excited singlet and triplet states, for example, heptazine, have recently been reported and gained substantial attention since they violate the famous Hund's rule. Utilizing state-of-the-art high-level ab initio methods, the singlet-triplet gap vanishes and approaches zero from below whatever is improved in the theoretical description of the molecules: the basis set or the level of electron correlation. Seemingly, the phenomenon of inverted singlet-triplet gaps tends to vanish the closer we observe.
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Affiliation(s)
- Andreas Dreuw
- Interdisciplinary Center for Scientific Computing, Ruprecht-Karls University, Heidelberg, Germany
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18
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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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19
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Blasco D, Nasibullin RT, Valiev RR, Sundholm D. Gold( i)-containing light-emitting molecules with an inverted singlet–triplet gap †. Chem Sci 2023; 14:3873-3880. [PMID: 37035700 PMCID: PMC10074427 DOI: 10.1039/d3sc00345k] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2023] [Accepted: 02/15/2023] [Indexed: 04/08/2023] Open
Abstract
Delayed fluorescence from molecules with an inverted singlet–triplet gap (DFIST) is the consequence of the unusual reverse order of the lowest excited singlet (S1) and triplet (T1) states of thermally activated delayed fluorescence (TADF) emitters. Heptazine (1,3,4,6,7,9,9b-heptaazaphenalene) derivatives have an inverted singlet–triplet gap thanks to the combination of multiple resonance (MR) effects and a significant double excitation character. Here, we study computationally the effect of gold(i) metalation and coordination on the optical properties of heptazine (molecule 4) and the phosphine-functionalized 2,5,8-tris(dimethylphosphino)heptazine derivatives (molecules 1–3). Ab initio calculations at the approximate second-order coupled cluster (CC2) and extended multiconfigurational quasi degenerate perturbation theory at the second order (XMC-QDPT2) levels show that molecules 1–4 have an inverted singlet–triplet gap due to the alternating spatial localization of the electron and hole of the exciton in the heptazine core. A non-vanishing one-electron spin–orbit coupling operator matrix element between T1 and and a fast S1 ← T1 intersystem crossing rate constant (kISC) calculated at the XMC-QDPT2(12,12) level of theory for molecule 4 suggest that this new family of complexes may be the first organometallic DFIST emitters reported. Substitution with gold(i)-containing moieties results in non-vanishing oscillator strengths and spin–orbit coupling leading to fast intersystem crossing in light-emitting heptazine derivates with an inverted singlet–triplet gap.![]()
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Affiliation(s)
- Daniel Blasco
- Department of Chemistry, Faculty of Science, University of HelsinkiP.O. Box 55, (A.I. Virtasen Aukio 1)FIN-00014Finland
- Departamento de Química, Centro de Investigación en Síntesis Química (CISQ), Universidad de La RiojaMadre de Dios 5326006LogroñoSpain
| | | | - Rashid R. Valiev
- Department of Chemistry, Faculty of Science, University of HelsinkiP.O. Box 55, (A.I. Virtasen Aukio 1)FIN-00014Finland
| | - Dage Sundholm
- Department of Chemistry, Faculty of Science, University of HelsinkiP.O. Box 55, (A.I. Virtasen Aukio 1)FIN-00014Finland
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