EPR Characterization of the Quintet State for a Hydrocarbon Tetraradical with Two Localized 1,3-Cyclopentanediyl Biradicals Linked by <i>meta</i>-Phenylene as a Ferromagnetic Coupler

Adam, Waldemar; Barneveld, Claus van; Bottle, Steven E.; Engert, Heinrich; Hanson, Graeme R.; Harrer, Heinrich M.; Heim, Christiane; Nau, Werner M.; Wang, Biao

doi:10.1021/ja953494m

Cited by 29 publications

(31 citation statements)

References 20 publications

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“…[1][2][3][4][5][6][7][8][9][10][11][12][13]38,41,48,53,54 DBO and its derivatives are special examples, because many of them are photochemically "persistent" azoalkanes, which show fascinating photophysical properties instead. 3,38,52,55 Besides an unexpectedly short phosphorescence lifetime, 41 DBO exhibits a very broad fluorescence spectrum 52 and an exceedingly long fluorescence lifetime (up to 1 µs in the gas phase).…”

Section: Photophysical Characterizationmentioning

confidence: 99%

“…[1][2][3] They have remained key intermediates in the synthesis of strained compounds 1,4 and in the mechanistic investigation of the behavior of biradicals, [5][6][7][8][9][10][11] with some seemingly never-ending mechanistic disputes like the double-inversion peculiarity of 2,3-diazabicyclo[2.2.1]hept-2-enes. 12,13 Derivatives of 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO, 1) have recently become valuable structural and dynamic probes 14 as well as sensors for supramolecular [15][16][17][18][19][20][21][22][23] and biomolecular assemblies.…”

Section: Introductionmentioning

confidence: 99%

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Bridgehead carboxy-substituted 2,3-diazabicyclo[2.2.2]oct-2-enes: synthesis, fluorescent properties, and host-guest complexation

Hennig¹,

Schwarzlose²,

Nau³

2007

Arkivoc

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Two novel derivatives of 2,3-diazabicyclo[2.2.2]oct-2-ene were synthesized, carrying a carboxyl (4) and a methylcarboxyl (5) substituent at the bridgehead position. The photodecomposition quantum yields (51% for 4 and 2.9% for 5) and fluorescence lifetimes (29 ns for 4 and 345 ns for 5) in water were determined. The higher photoreactivity and fluorescence quenching for 4 was attributed to its higher propensity to undergo photochemical elimination of nitrogen as a consequence of the presence of the radical-stabilizing carboxyl group in the α-position. The absolute photodecomposition rate constants of 4 became faster upon protonation (e.g., at pH 2), which contrasted anticipated substituent effects on the C-N bonds strengths. ) which was attributed to reduced Coulomb attractions as a consequence of the 1,3-alternate conformation which this host adopts in water. The binding constants towards β-cyclodextrin were also low at pH 7.0 (< 120 M -1 ), which was attributed to the low hydrophobicity of the anionic form of the guests; in line with this interpretation, the binding constants with β-cyclodextrin increased at pH 2.0, by about one order of magnitude.

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Section: Photophysical Characterizationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Bridgehead carboxy-substituted 2,3-diazabicyclo[2.2.2]oct-2-enes: synthesis, fluorescent properties, and host-guest complexation

Hennig¹,

Schwarzlose²,

Nau³

2007

Arkivoc

Self Cite

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“…3, structures 2 and 3 [1, 2] and structure 4 [5]) and Adam [4] (Fig. 3, structure 5), which have been shown experimentally to be quintets in the ground state.…”

Section: Computational Detailsmentioning

confidence: 99%

“…In the systems studied by Dougherty et al [2] (and those recently synthesized by Adam et al [4]), the SC units are triplets (as isolated molecules) coupled via the FC unit. In this case, Dougherty proposes to model [2] the interaction of two triplets, considering a phenomenological Hamiltonian of the form r À2t 1 Á 2 1 where 1 and 2 are the spin operators for the SC units and t is the coupling parameter (or eective exchange integral).…”

Section: Introductionmentioning

confidence: 99%

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

Lafuente

Novoa

Bearpark

et al. 1999

Theoretical Chemistry Accounts: Theory, Computation, and Modeli

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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, t , into contributions from individual active orbital sites and a decomposition of the spin multiplicity into terms from the ferromagnetic coupling unit and the spincontaining 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.

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“…Magnetic properties of open‐shell molecules have been extensively studied for materials science and basic research . In particular, well‐designable organic radicals have attracted much attention for the development of high‐spin materials.…”

Section: Introductionmentioning

confidence: 99%

Electron‐spin resonance (ESR) characterization of quintet spin‐state bis‐nitroxide‐bearing cyclopentane‐1,3‐diyl diradicals

Omokawa

Hatano

Abe

2014

J of Physical Organic Chem

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High-spin organic molecules have attracted much attention as spin sources for magnetic materials. In this paper, a novel high-spin organic molecule was designed according to a logical strategy. A 2,2-dimethylcyclopentane-1,3-diyl diradical unit was utilized as a spin source and a spin-bridged fragment. In addition, nitroxides were introduced as spin sources. Quintet electron-spin resonance (ESR) signals, which were attributed to the 1,3-di(3′-nitoroxyphenyl)-2,2-dimethylcyclopentane-1,3-diyl tetraradical (TR), were observed in a 2-methyltetrahydrofuran glassy matrix at 80 K after the photodenitrogenation of a newly synthesized azoalkanes AZ. A simulation of the signal provided the zero-field splitting parameters D (|D|/hc = 0.0127 cm À1) and E (|E|/hc = 0.0014 cm À1) for the quintet state of the tetraradical TR. The parameter D of the quintet state of TR was found similar to those of the previously reported quintet spin states of tetraradical TR1 with two cyclobutane-1,3-diyl units (0.0190 cm À1) and TR2 with two 2,2-dimethylcyclopentane-1,3-diyl diradicals (0.0116 cm À1).

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EPR Characterization of the Quintet State for a Hydrocarbon Tetraradical with Two Localized 1,3-Cyclopentanediyl Biradicals Linked by meta-Phenylene as a Ferromagnetic Coupler

Cited by 29 publications

References 20 publications

Bridgehead carboxy-substituted 2,3-diazabicyclo[2.2.2]oct-2-enes: synthesis, fluorescent properties, and host-guest complexation

Bridgehead carboxy-substituted 2,3-diazabicyclo[2.2.2]oct-2-enes: synthesis, fluorescent properties, and host-guest complexation

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

Electron‐spin resonance (ESR) characterization of quintet spin‐state bis‐nitroxide‐bearing cyclopentane‐1,3‐diyl diradicals

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