1
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Sentyurin VV, Levitskiy OA, Yankova TS, Grishin YK, Lyssenko KA, Goloveshkin AS, Alabugin IV, Magdesieva TV. Double Spin with a Twist: Synthesis and Characterization of a Neutral Mixed-Valence Organic Stable Diradical. J Am Chem Soc 2024; 146:26261-26274. [PMID: 39259835 DOI: 10.1021/jacs.4c08167] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/13/2024]
Abstract
A convenient design strategy opens access to neutral open-shell mixed-valence species via the redox transformation of charged stable precursors, i.e., the spiro-fused borate anions. We have implemented this strategy for the synthesis of the first neutral mixed-valence diradical: two neutral mixed-valence radical fragments were assembled via a twisted biphenyl bridge. The diradical is a crystalline solid obtained in almost quantitative yield by using a facile synthetic procedure. It is stable at room temperature in the triplet ground state with a very small singlet/triplet gap. This metal-free diradical can reversibly form five redox states. The diradical exhibits an intense IVCT band in the NIR region and can be assigned as a Class 2 Robin-Day MV (mixed valence) system with weakly interacting redox centers. Computations suggest that this diradical finds itself in a unique tug-of-war between two electron delocalization patterns, Kekulé and non-Kekulé, which gives rise to two geometric isomers that are close in energy but drastically different in spin distribution and polarity. Such bistable spin-systems should be intrinsically switchable and promising for the design of functional spin devices. The scope and limitations of the new redox-strategy for the neutral MV radicals were also tested on other types of spiro-fused borates, revealing structural factors responsible for the evolution from transient to persistent and then to stable radicals.
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Affiliation(s)
- Vyacheslav V Sentyurin
- Department of Chemistry, Lomonosov Moscow State University, Leninskie Gory 1/3, Moscow 119991, Russia
| | - Oleg A Levitskiy
- Department of Chemistry, Lomonosov Moscow State University, Leninskie Gory 1/3, Moscow 119991, Russia
| | - Tatiana S Yankova
- Department of Chemistry, Lomonosov Moscow State University, Leninskie Gory 1/3, Moscow 119991, Russia
| | - Yuri K Grishin
- Department of Chemistry, Lomonosov Moscow State University, Leninskie Gory 1/3, Moscow 119991, Russia
| | - Konstantin A Lyssenko
- Department of Chemistry, Lomonosov Moscow State University, Leninskie Gory 1/3, Moscow 119991, Russia
| | - Alexander S Goloveshkin
- A.N.Nesmeyanov Institute of Organoelement Compounds of Russian Academy of Sciences, Vavilova St. 28, Moscow 119934, Russia
| | - Igor V Alabugin
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306-4390, United States
| | - Tatiana V Magdesieva
- Department of Chemistry, Lomonosov Moscow State University, Leninskie Gory 1/3, Moscow 119991, Russia
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2
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Mishra S, Vilas-Varela M, Fatayer S, Albrecht F, Peña D, Gross L. Observation of SOMO-HOMO Inversion in a Neutral Polycyclic Conjugated Hydrocarbon. ACS NANO 2024; 18:15898-15904. [PMID: 38833667 PMCID: PMC11191738 DOI: 10.1021/acsnano.4c03257] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2024] [Revised: 05/17/2024] [Accepted: 05/24/2024] [Indexed: 06/06/2024]
Abstract
We report the generation of a nonbenzenoid polycyclic conjugated hydrocarbon, which consists of a biphenyl moiety substituted by indenyl units at the 4,4' positions, on ultrathin sodium chloride films by tip-induced chemistry. Single-molecule characterization by scanning tunneling and atomic force microscopy reveals an open-shell biradical ground state with a peculiar electronic configuration wherein the singly occupied molecular orbitals (SOMOs) are lower in energy than the highest occupied molecular orbital (HOMO).
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Affiliation(s)
| | - Manuel Vilas-Varela
- Center
for Research in Biological Chemistry and Molecular Materials (CiQUS)
and Department of Organic Chemistry, University
of Santiago de Compostela, Santiago de Compostela 15782, Spain
| | - Shadi Fatayer
- Applied
Physics Program, Physical Science and Engineering Division, King Abdullah University of Science and Technology
(KAUST), Thuwal 23955-6900, Kingdom
of Saudi Arabia
| | | | - Diego Peña
- Center
for Research in Biological Chemistry and Molecular Materials (CiQUS)
and Department of Organic Chemistry, University
of Santiago de Compostela, Santiago de Compostela 15782, Spain
- Oportunius, Galician
Innovation Agency (GAIN), Santiago
de Compostela 15702, Spain
| | - Leo Gross
- IBM
Research Europe − Zurich, Rüschlikon 8803, Switzerland
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3
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Zhang L, Li H, Zhu Y, Zhang S. A quantum-chemical insight into SOMO-HOMO conversion in phosphorus-boron cation radicals. Phys Chem Chem Phys 2024; 26:8273-8286. [PMID: 38385562 DOI: 10.1039/d4cp00098f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/23/2024]
Abstract
Organic radicals exhibiting SOMO-HOMO conversion (SHC) electronic configurations have recently garnered increasing attention due to their exceptional stability and photophysical properties. In this study, we investigate two series of phosphorus-boron cation radicals based on 1,3,5-trimethylphenyl units substituted with P and B atoms, varying numbers of P-B moieties, and π-conjugation linkers. We perform quantum-chemical calculations to systematically assess the influence of chemical substituents on the SHC electronic structural features. Our computational results demonstrate that the SHC electronic configurations of the studied complexes are primarily determined by the number of P-B moieties, specifically, phosphorus-boron cation radicals with two P-B moieties as terminal groups in π-conjugation linkers, which efficiently arrange electrons to increase HOMO energies compared to corresponding radicals with only one P-B unit. Furthermore, spin density distributions change as the size of π-conjugation linkers increases. Natural bond orbital (NBO) and atoms-in-molecules (AIM) analyses reveal strong intramolecular charge transfer between P and B atoms along with other stabilized donor-acceptor interactions and significant covalent bonds between P and B atoms. Moreover, synergistic effects resulting from 1,3,5-trimethylphenyl substitutions and enlarged π-conjugation linkers containing P-B units confer excellent photophysical properties upon these studied radicals, making them potential stable radicals in optoelectronic applications.
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Affiliation(s)
- Li Zhang
- School of Electronic Engineering, Guangxi University of Science and Technology, Liuzhou 545000, Guangxi, China.
| | - Hongbo Li
- School of Electronic Engineering, Guangxi University of Science and Technology, Liuzhou 545000, Guangxi, China.
| | - Yanbin Zhu
- School of Electronic Engineering, Guangxi University of Science and Technology, Liuzhou 545000, Guangxi, China.
| | - Shoufeng Zhang
- School of Electronic Engineering, Guangxi University of Science and Technology, Liuzhou 545000, Guangxi, China.
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Ajaykamal T, Palaniandavar M. Mononuclear nickel(ii)-flavonolate complexes of tetradentate tripodal 4N ligands as structural and functional models for quercetin 2,4-dioxygenase: structures, spectra, redox and dioxygenase activity. RSC Adv 2023; 13:24674-24690. [PMID: 37601601 PMCID: PMC10436029 DOI: 10.1039/d3ra04834a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2023] [Accepted: 08/01/2023] [Indexed: 08/22/2023] Open
Abstract
Three new nickel(ii)-flavonolate complexes of the type [Ni(L)(fla)](ClO4) 1-3, where L is the tripodal 4N ligand tris(pyrid-2-ylmethyl)amine (tpa, L1) or (pyrid-2-ylmethyl)bis(6-methylpyrid-2-ylmethyl)amine (6-Me2-tpa, L2) or tris(N-Et-benzimidazol-2-ylmethyl)amine (Et-ntb, L3), have been isolated as functional models for Ni(ii)-containing quercetin 2,4-dioxygenase. Single crystal X-ray structures of 1 and 3 reveal that Ni(ii) is involved in π-back bonding with flavonolate (fla-), as evident from enhancement in C[double bond, length as m-dash]O bond length upon coordination [H(fla), 1.232(3); 1, 1.245(7); 3, 1.262(8) Å]. More asymmetric chelation of fla- in 3 than in 1 [Δd = (Ni-Ocarbonyl - Ni-Oenolate): 1, 0.126; 3, 0.182 Å] corresponds to lower π-delocalization in 3 with electron-releasing N-Et substituent. The optimized structures of 1-3 and their geometrical isomers have been computed by DFT methods. The HOMO and LUMO, both localized on Ni(ii)-bound fla-, are highly conjugated bonding π- and antibonding π*-orbitals respectively. They are located higher in energy than the Ni(ii)-based MOs (HOMO-1, dx2-y2; HOMO-2/6, dz2), revealing that the Ni(ii)-bound fla- rather than Ni(ii) would undergo oxidation upon exposure to dioxygen. The results of computational studies, in combination with spectral and electrochemical studies, support the involvement of redox-inactive Ni(ii) in π-back bonding with fla-, tuning the π-delocalization in fla- and hence its activation. Upon exposure to dioxygen, all the flavonolate adducts in DMF solution decompose to produce CO and depside, which then is hydrolyzed to give the corresponding acids at 70 °C. The highest rate of dioxygenase reactivity of 3 (kO2: 3 (29.10 ± 0.16) > 1 (16.67 ± 0.70) > 2 (1.81 ± 0.04 × 10-1 M-1 s-1)), determined by monitoring the disappearance of the LMCT band in the range 440-450 nm, is ascribed to the electron-releasing N-Et substituent on bzim ring, which decreases the π-delocalization in fla- and enhances its activation.
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Affiliation(s)
- Tamilarasan Ajaykamal
- Department of Chemistry, Bharathidasan University Tiruchirapalli 620 024 Tamil Nadu India +91-431-2407043 +91-431-2407125
| | - Mallayan Palaniandavar
- Department of Chemistry, Bharathidasan University Tiruchirapalli 620 024 Tamil Nadu India +91-431-2407043 +91-431-2407125
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5
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Li Y, Ding Z, Mu Q, Ren J, Shen Q, Zhang S, Zhang L. Theoretical investigations on P-stabilized boryl cation radicals: from the Aufbau principle to SOMO-HOMO conversion. Dalton Trans 2023; 52:384-393. [PMID: 36519378 DOI: 10.1039/d2dt02723b] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
We report the characterization of a series of novel phosphinidene-stabilized (P-stabilized) boryl cation radicals, in which the phosphinidene and boryl are stabilised by iPrNHC (iPrNHC[:C{N(iPr)C(H)}2]), and the P-stabilized boryl (P → B) moieties are linked by 1,8-naphthalene (1PB-a), 1,10-biphenyl (1PB-b), 1,2-perylene (1PB-c), and 4,5-perylene (1PB-d), to form a series of 1PB compounds. The 2PB series is designed by adding another P-stabilized boryl (P → B) unit into the 1PB series, in which the two P-stabilized boryl (P → B) moieties for each 2PB compound are linked by 1,4,5,8-naphthalene, (2PB-a), 1,5,6,10-biphenyl (2PB-b), 1,2,7,8-perylene (2PB-c), and 4,5,10,11-perylene (2PB-d), respectively. Theoretical calculations demonstrate that for all the studied molecules, the spin density mainly locates on the B atoms. Interestingly, the series of 2PB(a-d) compounds possess SOMO-HOMO conversion properties, while 1PB(a-d) compounds obey the Aufbau principle, resulting from the difference in the number of the P-stabilized boryl (P → B) moieties and an increase of the π-conjugation bridge that lead to the significantly increased HOMO energy in 2PB(a-d) compounds, which should be responsible for the different structural properties of compounds 1PB(a-d) and 2PB(a-d). The natural bond orbital (NBO) and atoms in molecules (AIM) analysis reveal how the interactions contribute to the covalent bond between P and B atoms. Moreover, the absorption properties show that the spectra of the 2PB(a-d) compounds are red-shifted relative to those of the corresponding 1PB(a-d) compounds in the near infrared region. We hope this work can provide new insights into tuning the electronic structures of the well-defined forms of P-stabilized boryl cation radicals and expand their potential application in organic optoelectronics.
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Affiliation(s)
- Yuyao Li
- School of Electronic Engineering, Guangxi University of Science and Technology, Liuzhou 545000, Guangxi, China. .,School of Automation, Guangxi University of Science and Technology, Liuzhou 545000, Guangxi, China
| | - Zhelin Ding
- School of Electronic Engineering, Guangxi University of Science and Technology, Liuzhou 545000, Guangxi, China. .,School of Automation, Guangxi University of Science and Technology, Liuzhou 545000, Guangxi, China
| | - Qiqi Mu
- School of Electronic Engineering, Guangxi University of Science and Technology, Liuzhou 545000, Guangxi, China. .,School of Automation, Guangxi University of Science and Technology, Liuzhou 545000, Guangxi, China
| | - Junle Ren
- School of Electronic Engineering, Guangxi University of Science and Technology, Liuzhou 545000, Guangxi, China. .,School of Automation, Guangxi University of Science and Technology, Liuzhou 545000, Guangxi, China
| | - Qiguang Shen
- School of Electronic Engineering, Guangxi University of Science and Technology, Liuzhou 545000, Guangxi, China. .,School of Automation, Guangxi University of Science and Technology, Liuzhou 545000, Guangxi, China
| | - Shoufeng Zhang
- School of Electronic Engineering, Guangxi University of Science and Technology, Liuzhou 545000, Guangxi, China.
| | - Li Zhang
- School of Electronic Engineering, Guangxi University of Science and Technology, Liuzhou 545000, Guangxi, China.
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6
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Kasemthaveechok S, Abella L, Crassous J, Autschbach J, Favereau L. Organic radicals with inversion of SOMO and HOMO energies and potential applications in optoelectronics. Chem Sci 2022; 13:9833-9847. [PMID: 36128246 PMCID: PMC9430691 DOI: 10.1039/d2sc02480b] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2022] [Accepted: 07/06/2022] [Indexed: 11/21/2022] Open
Abstract
Organic radicals possessing an electronic configuration in which the energy of the singly occupied molecular orbital (SOMO) is below the highest doubly occupied molecular orbital (HOMO) level have recently attracted significant interest, both theoretically and experimentally. The peculiar orbital energetics of these SOMO-HOMO inversion (SHI) organic radicals set their electronic properties apart from the more common situation where the SOMO is the highest occupied orbital of the system. This review gives a general perspective on SHI, with key fundamental aspects regarding the electronic and structural factors that govern this particular electronic configuration in organic radicals. Selected examples of reported compounds with SHI are highlighted to establish molecular guidelines for designing this type of radical, and to showcase the potential of SHI radicals in organic spintronics as well as for the development of more stable luminescent radicals for OLED applications.
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Affiliation(s)
| | - Laura Abella
- Department of Chemistry, University at Buffalo, State University of New York Buffalo New York 14260 USA
| | | | - Jochen Autschbach
- Department of Chemistry, University at Buffalo, State University of New York Buffalo New York 14260 USA
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7
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Kasemthaveechok S, Abella L, Jean M, Cordier M, Vanthuyne N, Guizouarn T, Cador O, Autschbach J, Crassous J, Favereau L. Carbazole Isomerism in Helical Radical Cations: Spin Delocalization and SOMO-HOMO Level Inversion in the Diradical State. J Am Chem Soc 2022; 144:7253-7263. [PMID: 35413200 DOI: 10.1021/jacs.2c00331] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We report a new molecular design to afford persistent chiral organic open-shell systems with configurational stability and an inversion in energy of the singly occupied molecular orbital (SOMO) and the highest doubly occupied molecular orbital (HOMO) for both mono- and diradical states. The unpaired electron delocalization within the designed extended helical π-conjugated systems is a crucial factor to reach chemical stabilities, which is not obtained using the classical steric protection approach. The unique features of the obtained helical monoradicals allow an exploration of the chiral intramolecular electron transfer (IET) process in solvents of different polarity by means of optical and chiroptical spectroscopies, resulting in an unprecedented electronic circular dichroism (ECD) sign inversion for the radical transitions. We also characterized the corresponding helical diradicals, which show near-infrared electronic circular dichroism at wavelengths up to 1100 nm and an antiferromagnetic coupling between the spins, with an estimated singlet-triplet gap (ΔEST) of about -1.2 kcal mol-1. The study also revealed an intriguing double SOMO-HOMO inversion (SHI) electronic configuration for these diradicals, providing new insight regarding the peculiar energetic ordering of radical orbitals and the impact on the corresponding (chiral) optoelectronic properties.
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Affiliation(s)
| | - Laura Abella
- Department of Chemistry, University at Buffalo, State University of New York, Buffalo, New York 14260, United States
| | - Marion Jean
- Aix Marseille University, CNRS Centrale Marseille, iSm2, 13284 Marseille, France
| | - Marie Cordier
- Univ Rennes, CNRS, ISCR - UMR 6226, F-35000 Rennes, France
| | - Nicolas Vanthuyne
- Aix Marseille University, CNRS Centrale Marseille, iSm2, 13284 Marseille, France
| | | | - Olivier Cador
- Univ Rennes, CNRS, ISCR - UMR 6226, F-35000 Rennes, France
| | - Jochen Autschbach
- Department of Chemistry, University at Buffalo, State University of New York, Buffalo, New York 14260, United States
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Proton-induced Conversion from Non-Aufbau to Aufbau Electronic Structure of an Organic Radical with Turn-on Fluorescence. Chem Res Chin Univ 2022. [DOI: 10.1007/s40242-022-2015-z] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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9
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A functional model for quercetin 2,4-dioxygenase: Geometric and electronic structures and reactivity of a nickel(II) flavonolate complex. J Inorg Biochem 2021; 226:111632. [PMID: 34700128 DOI: 10.1016/j.jinorgbio.2021.111632] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2021] [Revised: 10/06/2021] [Accepted: 10/12/2021] [Indexed: 11/22/2022]
Abstract
Quercetin 2,4-dioyxgenase (QueD) has been known to catalyze the oxygenative degradation of flavonoids and quercetin. Recent crystallographic study revealed a nickel ion occupies the active site as a co-factor to support O2 activation and catalysis. Herein, we report a nickel(II) flavonolate complex bearing a tridentate macrocyclic ligand, [NiII(Me3-TACN)(Fl)(NO3)](H2O) (1, Me3-TACN = 1,4,7-trimethyl-1,4,7-triazacyclononane, Fl = 3-hydroxyflavone) as a functional model for QueD. The flavonolatonickel(II) complex was characterized by using spectrometric analysis including UV-vis spectroscopy, electrospray ionization mass spectrometer (ESI-MS), infrared spectroscopy (FT-IR) and 1H nuclear magnetic resonance spectroscopy (NMR). The single crystal X-ray structure of 1 shows two isomers with respect to the direction of a flavonolate ligand. Two isomers commonly are in the octahedral geometry with a bidentate of flavonolate and a monodentate of nitrate as well as a tridentate binding of Me3-TACN ligand. The spin state of 1 is determined to be a triplet state based on the Evans' method. Interestingly, electronic configuration of 1 from density functional theory (DFT) calculations revealed that the two singly occupied molecular orbitals (SOMOs) lie energetically lower than the highest (doubly) occupied molecular orbital (HOMO), that is so-called the SOMO-HOMO level inversion (SHI). The HOMO shows an electron density localized in the flavonolate ligand, indicating that flavonolate ligand is oxidized first rather than the nickel center. Thermal degradation of 1 resulted in the formation of benzoic acid and salicylic acid, which is attributed to the oxygenation of flavonolate of 1.
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Murata R, Wang Z, Abe M. Singly Occupied Molecular Orbital−Highest Occupied Molecular Orbital (SOMO−HOMO) Conversion. Aust J Chem 2021. [DOI: 10.1071/ch21186] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Singly occupied molecular orbital−highest occupied molecular orbital (SOMO−HOMO) conversion (inversion), SHC, is a phenomenon in which the SOMO is lower in energy than the doubly occupied molecular orbitals (DOMO, HOMO). A non-Aufbau electronic structure leads to unique properties such as a switch in bond dissociation energy and the generation of high-spin species on one-electron oxidation. In addition, the pronounced photostability of these species has been reported recently for application in organic light-emitting devices. In this review article, we summarise the chemistry of SOMO−HOMO converted (inverted) species reported to date.
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