1
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Abstract
Robust organic triradicals with high-spin quartet ground states provide promising applications in molecular magnets, spintronics, etc. In this context, a triradical based on Blatter's radical has been synthesized recently, having two low-lying non-degenerate doublet states with a quartet ground state. The traditional broken-symmetry (BS)-DFT computed doublet-quartet energy gaps are reported to be somewhat overestimated in comparison to the experimentally observed values. In this work, we have employed different ab initio methods on this prototypical system to obtain more accurate doublet-quartet energy gaps for this triradical. The spin-constraint broken-symmetry (CBS)-DFT method has been used to reduce the overestimation of energy gaps from BS-DFT. To address the issues of spin-contamination and the multireference nature of low-spin states affecting the DFT methods, we have computed the energy gaps using appropriately state-averaged CASSCF and NEVPT2 computations. Using a series of active spaces, our calculations are shown to provide quite accurate values in concordance with the experimentally observed results. Furthermore, we have proposed and modeled another two triradicals based on Blatter's radical, which are of interest for experimental synthesis and characterization. Our computations show that all these triradicals also have a quartet ground state with a similar energy difference between the excited doublet states.
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Affiliation(s)
- Rishu Khurana
- Institute of Nano Science and Technology, Sector-81, Mohali, Punjab 140306, India
| | - Ashima Bajaj
- Institute of Nano Science and Technology, Sector-81, Mohali, Punjab 140306, India
| | - K R Shamasundar
- Indian Institute of Science Education and Research Mohali, Sector-81, Mohali, Punjab 140306, India
| | - Md Ehesan Ali
- Institute of Nano Science and Technology, Sector-81, Mohali, Punjab 140306, India
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2
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Boudalis AK, Constantinides CP, Chrysochos N, Carmieli R, Leitus G, Kourtellaris A, Lawson DB, Koutentis PA. Deciphering the ground state of a C 3-symmetrical Blatter-type triradical by CW and pulse EPR spectroscopy. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2023; 349:107406. [PMID: 36841142 DOI: 10.1016/j.jmr.2023.107406] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/08/2022] [Revised: 02/08/2023] [Accepted: 02/13/2023] [Indexed: 06/18/2023]
Abstract
3,3',3''-(Benzene-1,3,5-triyl)tris(1-phenyl-1H-benzo[e][1,2,4]triazin-4-yl) (1) is a C3-symmetrical triradical comprised of three Blatter radical units connected at the 1, 3, 5 positions of a central trimethylenebenzene core. This triradical has an excellent air, moisture, and thermal stability. Single-crystal XRD indicates that triradical 1 adopts a propeller-like geometry with the benzotriazinyl moieties twisted by 174.1(2)° and packs in 1D chains along the c axis to form an extensive network of weak intermolecular interactions. Frozen solution continuous wave (CW) EPR spectra and variable-temperature field-sweep echo-detected (FSED) spectra revealed an intramolecular ferromagnetic exchange within the spin system, supporting a quartet S = 3/2 ground state. DFT calculations further supported these experimental findings.
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Affiliation(s)
- Athanassios K Boudalis
- Institut de Chimie de Strasbourg (UMR 7177, CNRS-Unistra), Université de Strasbourg, 4 rue Blaise Pascal, CS 90032, F-67081 Strasbourg, France.
| | - Christos P Constantinides
- Department of Natural Sciences, University of Michigan - Dearborn, 4901 Evergreen Rd, Dearborn, MI 48128, United States.
| | - Nicolas Chrysochos
- Department of Chemistry, University of Cyprus, P.O. Box 20537, 1678 Nicosia, Cyprus
| | - Raanan Carmieli
- Department of Chemical Research Support, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Gregory Leitus
- Department of Chemical Research Support, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Andreas Kourtellaris
- Department of Chemistry, University of Cyprus, P.O. Box 20537, 1678 Nicosia, Cyprus
| | - Daniel B Lawson
- Department of Natural Sciences, University of Michigan - Dearborn, 4901 Evergreen Rd, Dearborn, MI 48128, United States
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3
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Revisiting the Synthesis of Functionally Substituted 1,4-Dihydrobenzo[ e][1,2,4]triazines. MOLECULES (BASEL, SWITZERLAND) 2022; 27:molecules27082575. [PMID: 35458773 PMCID: PMC9031768 DOI: 10.3390/molecules27082575] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/29/2022] [Revised: 04/11/2022] [Accepted: 04/14/2022] [Indexed: 11/22/2022]
Abstract
A series of novel 1,4-dihydrobenzo[1,2,4][e]triazines bearing an acetyl or ester moiety as a functional group at the C(3) atom of the 1,2,4-triazine ring were synthesized. The synthetic protocol is based on an oxidative cyclization of functionally substituted amidrazones in the presence of DBU and Pd/C. It was found that the developed approach is suitable for the preparation of 1,4-dihydrobenzo[e][1,2,4]triazines, but the corresponding Blatter radicals were isolated only in few cases. In addition, a previously unknown dihydrobenzo[e][1,2,4]triazolo[3,4-c][1,2,4]triazine tricyclic open-shell derivative was prepared. Studies of thermal behavior of the synthesized 1,4-dihydrobenzo[1,2,4][e]triazines revealed their high thermal stability (up to 240–250 °C), which enables their application potential as components of functional organic materials.
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4
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Zhang S, Pink M, Junghoefer T, Zhao W, Hsu SN, Rajca S, Calzolari A, Boudouris BW, Casu MB, Rajca A. High-Spin ( S = 1) Blatter-Based Diradical with Robust Stability and Electrical Conductivity. J Am Chem Soc 2022; 144:6059-6070. [PMID: 35333507 PMCID: PMC10439714 DOI: 10.1021/jacs.2c01141] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Triplet ground-state organic molecules are of interest with respect to several emerging technologies but usually show limited stability, especially as thin films. We report an organic diradical, consisting of two Blatter radicals, that possesses a triplet ground state with a singlet-triplet energy gap, ΔEST ≈ 0.4-0.5 kcal mol-1 (2J/k ≈ 220-275 K). The diradical possesses robust thermal stability, with an onset of decomposition above 264 °C (TGA). In toluene/chloroform, glassy matrix, and fluid solution, an equilibrium between two conformations with ΔEST ≈ 0.4 kcal mol-1 and ΔEST ≈ -0.7 kcal mol-1 is observed, favoring the triplet ground state over the singlet ground-state conformation in the 110-330 K temperature range. The diradical with the triplet ground-state conformation is found exclusively in crystals and in a polystyrene matrix. The crystalline neutral diradical is a good electrical conductor with conductivity comparable to the thoroughly optimized bis(thiazolyl)-related monoradicals. This is surprising because the triplet ground state implies that the underlying π-system is cross-conjugated and thus is not compatible with either good conductance or electron delocalization. The diradical is evaporated under ultra-high vacuum to form thin films, which are stable in air for at least 18 h, as demonstrated by X-ray photoelectron and electron paramagnetic resonance (EPR) spectroscopies.
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Affiliation(s)
- Shuyang Zhang
- Department of Chemistry, University of Nebraska, Lincoln, Nebraska 68588-0304, United States
| | - Maren Pink
- IUMSC, Department of Chemistry, Indiana University, Bloomington, Indiana 47405-7102, United States
| | - Tobias Junghoefer
- Institute of Physical and Theoretical Chemistry, University of Tübingen, 72076 Tübingen, Germany
| | - Wenchao Zhao
- Charles D. Davidson School of Chemical Engineering, Purdue University, West Lafayette, IN 47907, United States
| | - Sheng-Ning Hsu
- Charles D. Davidson School of Chemical Engineering, Purdue University, West Lafayette, IN 47907, United States
| | - Suchada Rajca
- Department of Chemistry, University of Nebraska, Lincoln, Nebraska 68588-0304, United States
| | | | - Bryan W. Boudouris
- Charles D. Davidson School of Chemical Engineering, Purdue University, West Lafayette, IN 47907, United States
- Department of Chemistry, Purdue University, West Lafayette, IN 47907, United States
| | - Maria Benedetta Casu
- Institute of Physical and Theoretical Chemistry, University of Tübingen, 72076 Tübingen, Germany
| | - Andrzej Rajca
- Department of Chemistry, University of Nebraska, Lincoln, Nebraska 68588-0304, United States
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Khurana R, Bajaj A, Ali ME. Tuning the magnetic properties of a diamagnetic di-Blatter's zwitterion to antiferro- and ferromagnetically coupled diradicals. Phys Chem Chem Phys 2022; 24:2543-2553. [PMID: 35024707 DOI: 10.1039/d1cp04807d] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
In the quest of obtaining organic molecular magnets based on stable diradicals, we have tuned the inherent zwitterionic ground state of tetraphenylhexaazaanthracene (TPHA), a molecule containing two Blatter's moieties, by adopting two different strategies. In the first strategy, we have increased the length of the coupler between the two radical moieties and observed a transition from the zwitterionic ground state to the diradicalized state. With a larger coupler, ferromagnetic interactions are realized based on density functional theory (DFT) and wave-function theory (WFT) based complete active space self-consistent field (CASSCF)-N-electron valence state perturbation theory (NEVPT2) methods. An analysis based on the extent of spin contamination, diradical character, CASSCF orbital occupation number, Head-Gordon's index, HOMO-LUMO and SOMOs energy gaps is demonstrated that marks the transition of the ground state in these systems. In another approach, we systematically explore the effect of push-pull substitution on the way to obtain molecules based on a TPHA skeleton with diradicaloid state and, in some cases, even a triplet ground state.
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Affiliation(s)
- Rishu Khurana
- Institute of Nano Science and Technology, Sector-81, Mohali, Punjab, 140306, India.
| | - Ashima Bajaj
- Institute of Nano Science and Technology, Sector-81, Mohali, Punjab, 140306, India.
| | - Md Ehesan Ali
- Institute of Nano Science and Technology, Sector-81, Mohali, Punjab, 140306, India.
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Shu C, Pink M, Junghoefer T, Nadler E, Rajca S, Casu MB, Rajca A. Synthesis and Thin Films of Thermally Robust Quartet ( S = 3/2) Ground State Triradical. J Am Chem Soc 2021; 143:5508-5518. [PMID: 33787241 DOI: 10.1021/jacs.1c01305] [Citation(s) in RCA: 27] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
High-spin (S = 3/2) organic triradicals may offer enhanced properties with respect to several emerging technologies, but those synthesized to date typically exhibit small doublet quartet energy gaps and/or possess limited thermal stability and processability. We report a quartet ground state triradical 3, synthesized by a Pd(0)-catalyzed radical-radical cross-coupling reaction, which possesses two doublet-quartet energy gaps, ΔEDQ ≈ 0.2-0.3 kcal mol-1 and ΔEDQ2 ≈ 1.2-1.8 kcal mol-1. The triradical has a 70+% population of the quartet ground state at room temperature and good thermal stability with onset of decomposition at >160 °C under an inert atmosphere. Magnetic properties of 3 are characterized by SQUID magnetometry in polystyrene glass and by quantitative EPR spectroscopy. Triradical 3 is evaporated under ultrahigh vacuum to form thin films of intact triradicals on silicon substrate, as confirmed by high-resolution X-ray photoelectron spectroscopy. AFM and SEM images of the ∼1 nm thick films indicate that the triradical molecules form islands on the substrate. The films are stable under ultrahigh vacuum for at least 17 h but show onset of decomposition after 4 h at ambient conditions. The drop-cast films are less prone to degradation in air and have a longer lifetime.
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Affiliation(s)
- Chan Shu
- Department of Chemistry, University of Nebraska, Lincoln, Nebraska 68588-0304, United States
| | - Maren Pink
- Department of Chemistry, Indiana University, Bloomington, Indiana 47405-7102, United States
| | - Tobias Junghoefer
- Institute of Physical and Theoretical Chemistry, University of Tübingen, 72076 Tübingen, Germany
| | - Elke Nadler
- Institute of Physical and Theoretical Chemistry, University of Tübingen, 72076 Tübingen, Germany
| | - Suchada Rajca
- Department of Chemistry, University of Nebraska, Lincoln, Nebraska 68588-0304, United States
| | - Maria Benedetta Casu
- Institute of Physical and Theoretical Chemistry, University of Tübingen, 72076 Tübingen, Germany
| | - Andrzej Rajca
- Department of Chemistry, University of Nebraska, Lincoln, Nebraska 68588-0304, United States
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Exner J, Maisuls I, Massolle A, Klabunde S, Hansen MR, Strassert CA, Neugebauer J, Eckert H, Studer A. Electronic effects in profluorescent benzotriazinyl radicals: a combined experimental and theoretical study. Phys Chem Chem Phys 2021; 23:2999-3007. [PMID: 33480922 DOI: 10.1039/d0cp05732k] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The synthesis, photophysical characterization, and quantum chemical calculations of a series of benzotriazinyl radicals and their styryl radical trapping products are presented. The benzotriazinyl radicals are non-luminescent but surprisingly the corresponding styryl radical trapping products exhibit high fluorescence quantum yields (up to 60% in some cases), making them highly valuable probes or labels. Additionally, the influence of the substitution pattern on the optical properties of the radical trapping products was observed experimentally and interpreted by means of quantum chemical calculations. Specific substitution patterns showed a bathochromic shift compared to the unsubstituted compound. Computationally, it was shown that this substitution pattern leads to a stronger energetic stabilization of the lowest unoccupied molecular orbital than the highest occupied molecular orbital. Analysis of the influence of the substitution pattern on the optical properties showed a bathochromic shift in several examples, which was interpreted by means of quantum chemical calculations.
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Affiliation(s)
- Jessica Exner
- Organisch-Chemisches Institut, Westfälische Wilhelms-Universität Münster, Corrensstraße 40, 48149 Münster, Germany.
| | - Iván Maisuls
- Institut für Anorganische und Analytische Chemie, CiMIC, SoN, Westfälische Wilhelms-Universität Münster, Corrensstraße 28/30, 48149 Münster, Germany. and CeNTech, Westfälische Wilhelms-Universität Münster, Heisenbergstraße 11, 48149 Münster, Germany
| | - Anja Massolle
- Organisch-Chemisches Institut, Westfälische Wilhelms-Universität Münster, Corrensstraße 40, 48149 Münster, Germany. and Center for Multiscale Theory and Computation, Westfälische Wilhelms-Universität Münster, Corrensstraße 40, 48149 Münster, Germany.
| | - Sina Klabunde
- Institut für Physikalische Chemie, Westfälische Wilhelms-Universität Münster, Corrensstraße 30, 48149 Münster, Germany.
| | - Michael R Hansen
- Institut für Physikalische Chemie, Westfälische Wilhelms-Universität Münster, Corrensstraße 30, 48149 Münster, Germany.
| | - Cristian A Strassert
- Institut für Anorganische und Analytische Chemie, CiMIC, SoN, Westfälische Wilhelms-Universität Münster, Corrensstraße 28/30, 48149 Münster, Germany. and CeNTech, Westfälische Wilhelms-Universität Münster, Heisenbergstraße 11, 48149 Münster, Germany
| | - Johannes Neugebauer
- Organisch-Chemisches Institut, Westfälische Wilhelms-Universität Münster, Corrensstraße 40, 48149 Münster, Germany. and Center for Multiscale Theory and Computation, Westfälische Wilhelms-Universität Münster, Corrensstraße 40, 48149 Münster, Germany.
| | - Hellmut Eckert
- Institut für Physikalische Chemie, Westfälische Wilhelms-Universität Münster, Corrensstraße 30, 48149 Münster, Germany. and Instituto de Fisica de São Carlos, Universidade de São Paulo, Avenida Trabalhador Sãocarlense 400, São Carlos, SP 13566-590, Brazil.
| | - Armido Studer
- Organisch-Chemisches Institut, Westfälische Wilhelms-Universität Münster, Corrensstraße 40, 48149 Münster, Germany.
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Bartos P, Hande AA, Pietrzak A, Chrostowska A, Kaszyński P. Substituent effects on the electronic structure of the flat Blatter radical: correlation analysis of experimental and computational data. NEW J CHEM 2021. [DOI: 10.1039/d1nj05137g] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Functionalized flat Blatter radicals were obtained and substituent effects on spectroscopy, electrochemistry, and stability were investigated by correlation and DFT methods.
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Affiliation(s)
- Paulina Bartos
- Faculty of Chemistry, University of Łódź, 91-403 Łódź, Poland
| | - Aniket A. Hande
- Faculty of Chemistry, University of Łódź, 91-403 Łódź, Poland
- Université de Pau et des Pays de l’Adour E2S UPPA, CNRS, IPREM 64000, Pau, France
| | - Anna Pietrzak
- Faculty of Chemistry, Łódź University of Technology, Żeromskiego 116, 90-024, Łódź, Poland
| | - Anna Chrostowska
- Université de Pau et des Pays de l’Adour E2S UPPA, CNRS, IPREM 64000, Pau, France
| | - Piotr Kaszyński
- Faculty of Chemistry, University of Łódź, 91-403 Łódź, Poland
- Centre of Molecular and Macromolecular Studies, Polish Academy of Sciences, 90-363 Łódź, Poland
- Department of Chemistry, Middle Tennessee State University, Murfreesboro, TN, 37132, USA
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Rogers FJM, Norcott PL, Coote ML. Recent advances in the chemistry of benzo[e][1,2,4]triazinyl radicals. Org Biomol Chem 2020; 18:8255-8277. [DOI: 10.1039/d0ob01394c] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Benzo[e][1,2,4]triazinyl, or Blatter radicals, are stable free radicals with customisable magnetic, spectroscopic and electrochemical properties, and wide-ranging applications in synthesis and functional materials.
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Affiliation(s)
- Fergus J. M. Rogers
- ARC Centre of Excellence for Electromaterials Science
- Research School of Chemistry
- Australian National University
- Canberra
- Australia
| | - Philip L. Norcott
- ARC Centre of Excellence for Electromaterials Science
- Research School of Chemistry
- Australian National University
- Canberra
- Australia
| | - Michelle L. Coote
- ARC Centre of Excellence for Electromaterials Science
- Research School of Chemistry
- Australian National University
- Canberra
- Australia
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