We describe preparation and magnetic properties of an organic pi-conjugated polymer with very large moment order at low temperatures. The is designed a density cross-links alternating connectivity radical modules unequal spin quantum numbers (S), macrocyclic S = 2 and, cross-linking (1/2) modules, which permits net values for either ferromagnetic or antiferromagnetic exchange couplings between the modules. In highly cross-linked polymer, effective corresponding to average about 5000 slow...

We report a molecular design that provides an intravenously injectable organic radical contrast agent (ORCA) for which the 1H water relaxivity (r1) is ca. 5 mM–1 s–1. The ORCA based on spirocyclohexyl nitroxide radicals and poly(ethylene glycol) chains conjugated to fourth-generation polypropylenimine dendrimer scaffold. metal-free has long shelf life selectively enhanced magnetic resonance imaging in mice over 1 h.

Triplet ground-state organic molecules are interesting with respect to several emerging technologies but typically exhibit limited stability. We report two diradicals, one of which possesses a triplet ground state (2J/kB = 234 ± 36 K) and robust stability at elevated temperatures. able sublime this high-spin diradical under high vacuum 140 °C no significant decomposition.

A series of sterically shielded pyrrolidine nitroxides were synthesized, and their reduction by ascorbate (vitamin C) indicate that nitroxide 3, a tetraethyl derivative 3-carboxy-PROXYL, is reduced at the slowest rate among known nitroxides, i.e., 60-fold slower than for 3-carboxy-PROXYL.

High spin ( S = 1) organic diradicals may offer enhanced properties with respect to several emerging technologies, but typically exhibit low singlet triplet energy gaps and possess limited thermal stability. We report ground state diradical 2 a large singlet-triplet gap, Δ EST ≥ 1.7 kcal mol-1, leading nearly exclusive population of at room temperature, good stability onset decomposition ∼160 °C under inert atmosphere. Magnetic the previously prepared 1 are characterized by SQUID...

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 diradical, consisting two Blatter radicals, that possesses a triplet ground state singlet-triplet energy gap, ΔEST ≈ 0.4-0.5 kcal mol-1 (2J/k 220-275 K). The diradical robust thermal onset decomposition above 264 °C (TGA). In toluene/chloroform, glassy matrix, and fluid solution, equilibrium between conformations 0.4...

The synthesis and characterization of a novel oligothiophene, in which the thiophene rings are annelated into [7]helicene with cross-conjugated pi-system, described. Such [7]helicenes may be viewed as fragments unprecedented carbon-sulfur (C(2)S)(n)() helix, possessing sulfur-rich molecular periphery. Racemic is based upon iterative alternation two steps: C-C bond homocouplings between beta-positions thiophenes annelation alpha-positions thiophenes. Asymmetric carried out using...

(−)-Sparteine-mediated asymmetric synthesis of di-n-octyl-substituted carbon−sulfur [11]helicene, a helical (C2S)n β-undecathiophene, is described. The atom-efficient routes rely on one-step tri-annelation or two-step di- and mono-annelation to provide enantiomeric excess (+)- (−)-[11]helicene, respectively. X-ray structures for homologous [11] [7]helicenes indicate similar curvatures. optical band gap, Eg ≈ 3.5 eV, estimated the helix polymer, with onset electron localization at n ≤ 7.

The radical cation of carbon-sulfur [7]helicene is configurationally stable in solution at room temperature. In contrast to the cations alpha-oligothiophenes, which form diamagnetic pi-dimers low temperature, this helical, cross-conjugated beta-oligothiophene shows a propensity toward dimerization.

Organic molecules with a strong preference for triplet ground states, in which the state is below lowest singlet by ≥10 kcal/mol, are typically short-lived and mostly detected as reactive intermediates. We now report derivative of aza-m-xylylene diradical large singlet−triplet energy gap (ΔEST) ∼10 comparable to ΔEST well-known intermediate m-xylylene diradical. The aminyl persists solution at room temperature on time scale minutes.

We report a relatively persistent, open-shell aza-thia[7]helicene with cross-conjugated electron-rich π-system. The singly occupied molecular orbital (SOMO) energy levels of both radical cation and neutral the [7]helicene are below highest (HOMO) levels, thereby violating Aufbau principle. is prepared from β-hexathiophene by three-step one-pot reaction, in which pyrrole ring constructed two consecutive C–N bond formations. Chemical oxidation converts helicene to its cation, while presence...

We report an air-stable diradical dication of chiral D2-symmetric conjoined bis[5]diazahelicene with unprecedented high-spin (triplet) ground state, singlet triplet energy gap, ΔEST = 0.3 kcal mol–1. The possesses closed-shell (Kekulé) resonance forms 16 π-electron perimeters. is monomeric in dibutyl phthalate (DBP) matrix at low temperatures, and it has a half-life more than 2 weeks ambient conditions the presence excess oxidant. A barrier ∼35 mol–1 been experimentally determined for...

High-spin (S = 3/2) organic triradicals may offer enhanced properties with respect to several emerging technologies, but those synthesized date typically exhibit small doublet quartet energy gaps and/or possess limited thermal stability and processability. We report a ground state triradical 3, by Pd(0)-catalyzed radical-radical cross-coupling reaction, which possesses two doublet-quartet gaps, ΔEDQ ≈ 0.2-0.3 kcal mol-1 ΔEDQ2 1.2-1.8 mol-1. The has 70+% population of the at room temperature...

We report high-spin aminyl triradicals with near-planar triphenylene backbones. Near-planarity of the fused radicals and 2,6,10-triphenylene ferromagnetic coupling unit (FCU), magnetically equivalent to three 3,4'-biphenyl FCUs, assures an effective 2pπ-2pπ overlap within cross-conjugated π-system, leading S = 3/2 (quartet) ground state that is well separated from low-spin excited doublet states. Thermal populations (S 1/2) states are detectable both by SQUID magnetometry electron...

We report a neutral high-spin diradical of chiral C2-symmetric bis[5]diazahelicene with ΔEST ≈ 0.4 kcal mol–1, as determined by EPR spectroscopy/SQUID magnetometry. The is the most persistent among all aminyl radicals reported to date factor 20, half-life up 6 days in 2-MeTHF at room temperature. Its triplet ground state and excellent persistence may be associated unique spin density distribution within dihydrophenazine moiety, which characterizes two effective 3-electron C–N bonds analogous...

ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTVery High-Spin Organic Polymer: π-Conjugated Hydrocarbon Network with Average Spin of S ≥ 40Andrzej Rajca, Suchada and Jirawat WongsriratanakulView Author Information Department Chemistry University Nebraska Lincoln, 68588-0304 Cite this: J. Am. Chem. Soc. 1999, 121, 26, 6308–6309Publication Date (Web):June 19, 1999Publication History Received18 March 1999Published online19 June inissue 1 July 1999https://doi.org/10.1021/ja990881dCopyright ©...

By an iterative route the oligothiophene 1, a fragment of unprecedented carbon–sulfur (C2S) helicene, was prepared. The properties 1 are widely determined by cross-conjugation annelated thiophene rings.

Compounds with highly annelated, chiral π-systems, such as tetraphenylenes and [n]helicenes, are known to possess strong properties high configurational stability, which prerequisites for many materials. This account describes the unfolding story about our research on synthesis X-ray crystallographic characterization of functionalized nonracemic tetra­phenylenes helical β-oligothiophenes, well related [n]helicene derivatives.

To determine the impact of electron−electron spin−spin interactions on electron spin relaxation rates, 1/T1 and 1/Tm were measured for nitroxide monoradical, diradical, tetraradical derivatives 1,3-alternate calix[4]arenes, two pegylated high-spin diradicals, an azine-linked diradical. The synthesis characterization by SQUID (superconducting quantum interference device) magnetometry one in which nitroxides are conformationally constrained to be coplanar with m-phenylene unit, is reported....

Nitroxide diradicals, in which nitroxides are annelated to m-phenylene forming tricyclic benzobisoxazine-like structures, have been synthesized and characterized by X-ray crystallography, magnetic resonance (EPR 1H NMR) spectroscopy, as well studies solution solid state. For the octamethyl derivative of benzobisoxazine nitroxide diradical, conformationally constrained moieties coplanar with m-phenylene, leading large values 2J (2J/k > 200 K 2J/k ≫ 300 state). all ortho para positions...

Abstract Site‐directed spin labeling and EPR spectroscopy offer accurate, sensitive tools for the characterization of structure function macromolecules their assemblies. A new rigid label, spirocyclohexyl nitroxide α‐amino acid its N ‐(9‐fluorenylmethoxycarbonyl) derivative, have been synthesized, which exhibit slow enough spin‐echo dephasing to permit accurate distance measurements by pulsed at temperatures up 125 K in 1:1 water/glycerol higher matrices with glass transition temperatures....

Aminyl tetraradicals with planar tetraazanonacene backbones have quintet (S = 2) ground states and do not show any detectable thermal population of the low-spin excited up to highest temperature investigated (100 K) in 2-methyltetrahydrofuran (2-MeTHF) matrix. This indicates that nearest electronic state (triplet) is at least ~0.3 kcal mol(-1) higher energy, is, triplet-quintet energy gap, ΔE(TQ) > 0.3 mol(-1), which consistent broken-symmetry-DFT-computed about 5 mol(-1). In concentrated...

One-dimensional (1D) spin-1 (S = 1) chain of organic radicals with low local magnetic anisotropy may provide a better understanding the low-dimensional magnetism. We report solid-state studies, including single crystal X-ray crystallography, air-stable tetraazacyclophane diradical dication salt 12·2+·2[Al(OC(CF3)2CH3)4]− triplet ground state (ΔEST ≈ 0.5 kcal mol–1). The behavior for 12·2+ at temperature is best modeled by 1D spin S 1 Heisenberg intrachain antiferromagnetic coupling J′/k −5.4...

Abstract The availability of bioresistant spin labels is crucial for the optimization site‐directed labeling protocols EPR structural studies biomolecules in a cellular context. As can affect proteins’ fold and/or function, having possibility to choose between different will increase probability produce spin‐labeled functional proteins. Here, we report synthesis and characterization iodoacetamide‐ maleimide‐functionalized based on gem ‐diethyl pyrroline structure. two nitroxide are compared...