Ferromagnetic Coupling Unit Research Articles

High-Spin S = 3/2 Ground-State Aminyl Triradicals: Toward High-Spin Oligo-Aza Nanographenes.

We report high-spin aminyl triradicals with near-planar triphenylene backbones. Near-planarity of the fused aminyl radicals and the 2,6,10-triphenylene ferromagnetic coupling unit (FCU), magnetically equivalent to three fused 3,4'-biphenyl FCUs, assures an effective 2pπ-2pπ overlap within the cross-conjugated π-system, leading to an S = 3/2 (quartet) ground state that is well separated from low-spin excited doublet states. Thermal populations of the low-spin (S = 1/2) excited states are detectable both by SQUID magnetometry and electron paramagnetic resonance (EPR) spectroscopy, providing doublet-quartet energy gaps, ΔEDQ, corresponding to >85% population of the quartet ground states at room temperature. Notably, EPR-based determination of ΔEDQ relies on direct detection of the quartet ground state and doublet excited states. The ΔEDQ values are 1.0-1.1 kcal mol-1, with the more sterically shielded triradical having the larger value. The half-life of the more sterically shielded triradical in 2-methyltetrahydrofuran (2-MeTHF) is about 6 h at room temperature. The less sterically shielded triradical in 2-MeTHF decomposes at 158 K with a half-life of about 4 h, while at 195 K, the half-life is still about 2 h. The dominant products of the decay of triradicals are the corresponding triamines, suggesting hydrogen atom abstraction from the solvent as the primary mechanism. This study expands the frontier of the open-shell PAHs/nanographenes, of which the unique electronic, nonlinear optical, and magnetic properties could be useful in the development of novel organic electronics, photonics, and spintronics.

Electronic and Molecular Structures of Dendrimeric High-spin Polycarbenes as Studied by CW and Pulsed ESR-based Electron Spin Transient Nutation Spectroscopy

Highly symmetric high-spin polycarbenes of π-conjugation, which are the first and second generations of the spin-mediated dendrimers based on phenylacetylenes, have been studied by cw and pulsed ESR spectroscopy. We measured pulsed ESR-based two-dimensional electron-spin transient nutation (2D-ESTN) spectra of the stabilized polycarbene systems connecting the phenylacetylene moieties at the meta-positions of benzene rings, and we determined their spin multiplicity with the help of a transition moment analysis. A septet ground state of the triscarbene system, which is the first generation of the phenylacetylene dendrimers, was unequivocally discriminated. It is indicated that the stable diphenylcarbene serves as a useful building block and the phenylacetylene dendrimer as a ferromagnetic coupling unit with robust spin polarization for super high-spin polymeric systems and super paramagnetic materials.

Electronic and Molecular Structures of Dendrimeric High-spin Polycarbenes as Studied by CW and Pulsed ESR-based Electron Spin Transient Nutation Spectroscopy

Highly symmetric high-spin polycarbenes of π-conjugation, which are the first and second generations of the spin-mediated dendrimers based on phenylacetylenes, have been studied by cw and pulsed ESR spectroscopy. We measured pulsed ESR-based two-dimensional electron-spin transient nutation (2D-ESTN) spectra of the stabilized polycarbene systems connecting the phenylacetylene moieties at the meta-positions of benzene rings, and we determined their spin multiplicity with the help of a transition moment analysis. A septet ground state of the triscarbene system, which is the first generation of the phenylacetylene dendrimers, was unequivocally discriminated. It is indicated that the stable diphenylcarbene serves as a useful building block and the phenylacetylene dendrimer as a ferromagnetic coupling unit with robust spin polarization for super high-spin polymeric systems and super paramagnetic materials.

EPR spectral determination of electronic substituent effects on the D values of hydrocarbon polyradicals (Quintet and septet spin states) composed of localized 1,3-cyclopentanediyl spin-carrying units linked by 1,3-Di- and 1,3,5-trimethylenebenzene ferromagnetic couplers

The parent and p-nitrophenyl-substituted diradicals D-3a,b (triplets), tetraradicals T-3a,b (quintets), and hexaradicals H-3a,b (septets) were photochemically generated in matrix-isolated form (toluene, 77 K) by successive denitrogenation of the trisazoalkanes 3a,b and EPR spectrally characterized. In these high-spin polyradicals the spin-spin interaction within the localized spin-carrying 1,3-cyclopentanediyl diradical unit is much stronger than within the cross-conjugated ferromagnetic coupling unit. Accordingly, a change of the electronic properties in the cyclopentanediyl unit affects decisively the D value of the whole polyradical. Therefore, the spin-accepting p-nitro group reduces the D value of the tetra- and hexaradical in the same amount as that of the diradical. Thus, irrespective of the spin multiplicity, the substituent stabilizes electronically the triplet (D-3a,b), quintet (T-3a,b), and septet (H-3a,b) species with equal efficacy.

A computational study of the Dougherty model for the prediction of high-spin states in organic chemistry

The model proposed by Dougherty for the design of high-spin organic systems has been studied from a quantitative point of view using a Heisenberg Hamiltonian formalism. This analysis leads to a decomposition of the phenomenological coupling parameter, J, into contributions from individual active orbital sites and a decomposition of the spin multiplicity into terms from the ferromagnetic coupling unit and the spin-containing units. An analysis of the origin of quintet stability has been carried out for four molecular systems with quintet ground states that have previously been synthesized by Dougherty and by Adam. The results indicate that the ferromagnetic coupling unit plays the dominant role in determining high-spin stability as suggested by Dougherty and gives some insights that may be useful in the rational design of high-spin systems.

An Improved Model for One-Dimensional Polaronic Ferromagnetism: Electrochemically Doped Poly(m-phenylenefuchsone)

The one-dimensional polaronic ferromagnet paradigm in polymer-based organic ferromagnets is investigated. The synthesis of poly(m-phenylenefuchsone) (PMPF, see Figure), which contains m-phenylene as ferromagnetic coupling unit and 2,6-di-tert-butyl fuchsone as spin coupling unit, is reported. Electrochemically doped PMPF is demonstrated to be superior to previous systems in several respects.

Do High-Spin Topology Rules Apply to Charged Polyradicals? Theoretical and Experimental Evaluation of Pyridiniums as Magnetic Coupling Units

Ab initio calculations on pyridine and pyridinium analogues of m-xylylene indicate that the neutral heterocycle is essentially equivalent to benzene as a ferromagnetic coupling unit, while the cationic pyridiniums behave much differently. Depending on the substitution pattern, a protonated pyridine can serve as a ferromagnetic coupling unit or an antiferromagnetic coupling unit. Both valence bond and molecular orbital arguments provide qualitative rationalizations of these results. In an effort to test the theoretical predictions, bis(trimethylenemethane) analogues of the pyridine and pyridinium biradicals were synthesized and analyzed by electron paramagnetic resonance spectroscopy. General support for the theoretical predictions is obtained.

Trichloro-2,6-pyridylene, a Good Ferromagnetic Coupling Unit between Two Persistent Carbon Radical Centers

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTTrichloro-2,6-pyridylene, a Good Ferromagnetic Coupling Unit between Two Persistent Carbon Radical CentersJ. Chaler, R. Carilla, A. Labarta, Ll. Fajari, J. Riera, and L. JuliaCite this: J. Org. Chem. 1994, 59, 15, 4107–4113Publication Date (Print):July 1, 1994Publication History Published online1 May 2002Published inissue 1 July 1994https://doi.org/10.1021/jo00094a020RIGHTS & PERMISSIONSArticle Views138Altmetric-Citations9LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (889 KB) Get e-Alerts Get e-Alerts

Evaluation of potential ferromagnetic coupling units: the bis(TMM) [bis(trimethylenemethane)] approach to high-spin organic molecules

Four new hydrocarbon tetraradicals, 1-4, each composed of two triplet trimethylenemethane (TMM) subunits linked by a potential ferromagnetic coupling unit (FC), were synthesized and characterized by variable-temperature electron paramagnetic resonance (EPR) spectroscopy. Simulation of the EPR powder spectra and a priori calculation of the zero-field splitting parameters aided spectral assignment. The Heisenberg Hamiltonian appears to quantitatively model relative spin-state energies in 1-4. In three cases ferromagnetic coupling was achieved, as evidenced by quintet ground states in the resulting tetraradicals. In one case, strong evidence for antiferromagnetic coupling was obtained.

4,6-Dimethoxy-1,3-phenylenebis(N-tert-butyl nitroxide) with a singlet ground state. Formal violation of a rule that m-phenylene serves as a robust ferromagnetic coupling unit

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXT4,6-Dimethoxy-1,3-phenylenebis(N-tert-butyl nitroxide) with a singlet ground state. Formal violation of a rule that m-phenylene serves as a robust ferromagnetic coupling unitFumio Kanno, Katsuya Inoue, Noboru Koga, and Hiizu IwamuraCite this: J. Am. Chem. Soc. 1993, 115, 3, 847–850Publication Date (Print):February 1, 1993Publication History Published online1 May 2002Published inissue 1 February 1993https://doi.org/10.1021/ja00056a003RIGHTS & PERMISSIONSArticle Views356Altmetric-Citations101LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (518 KB) Get e-AlertsSupporting Info (2)»Supporting Information Supporting Information Get e-Alerts

Approaches from High-Spin Organic Molecules to Organic Ferromagnets

ABSTRACTPseudo-two dimensional branched polycarbenes 1, 3, 5-[H(m-C6H4C:)n/3]3C6H3 (2)(n = 6, 9) were prepared. The measurement of their magnetization on a Faraday balance equipped with a light guide has revealed that 2(n = 6) has a tridecet ground state (S = 6.0). The m-phenylene skeleton as a dependable ferromagnetic coupling unit has also been applied with success to the synthesis of persistent systems, i.e., 5, by replacing each carbene center in linear polycarbenes 1 with a nitroxide. A necessary degree of steric protection of the radical centers was disclosed. Extension to real polymers 4 gave an only partly successful result.

ChemInform Abstract: Cyclobutane as a General Ferromagnetic Coupling Unit. Design and Synthesis of a New, Hydrocarbon Quintet.

AbstractThe synthesis is described by a scheme (no yields, no further details given except that the syn isomer of the adduct obtained from (IV) and (V) is unstable to hydrogenation conditions).

Cyclobutane as a general ferromagnetic coupling unit. Design and synthesis of a new, hydrocarbon quintet

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCyclobutane as a general ferromagnetic coupling unit. Design and synthesis of a new, hydrocarbon quintetJulia A. Novak, Rakesh Jain, and Dennis A. DoughertyCite this: J. Am. Chem. Soc. 1989, 111, 19, 7618–7619Publication Date (Print):September 1, 1989Publication History Published online1 May 2002Published inissue 1 September 1989https://doi.org/10.1021/ja00201a055RIGHTS & PERMISSIONSArticle Views133Altmetric-Citations30LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (250 KB) Get e-Alerts Get e-Alerts