1,3-Alternate calix[4]arene nitronyl nitroxide tetraradical and diradical: synthesis, X-ray crystallography, paramagnetic NMR spectroscopy, EPR spectroscopy, and magnetic studies

Synthesis, Optical Properties and Magnetic Studies of 2,6‐Bis(pyrazolylmethyl)pyridine Functionalized with Two Nitronyl Nitroxide Radicals

“…This finding indicates that net destabilization of the singlet-triplet equilibrium (ST) occurs below 4 K, thus only an estimate for the ST energy separation can be obtained from the trend, with 0.06 cm -1 Ͻ ∆E ST = 2J/k B Ͻ 0.6 cm -1 . Such strong attenuation of the exchange coupling mediated by C(sp 3 ) bonds is consistent with recent ∆E ST findings for calix [4]arene nitronyl nitroxide [27] and nitroxide [28] biradical systems in which the through-bond exchange coupling pathway was topologically defined by the conformationally constrained radical-m-phenylene-C(sp 3 )-m-phenylene-radical synthetic designs.…”

Revisiting the Ullman's Radical Chemistry for Phthalocyanine Derivatives

“…[7] Condensationp roducts suffer from low solubility.C onsequently,t heir purificationa nd characterization are always ad ifficult task and the Ullman's synthesis is general-ly continued withoutf urtherp urification. Their lows olubility in methanol as well as the stabilization of the aldehyde function by resonance prevents the condensation with 6 in an appropriate manner.D espite these constraints, the Ullman radicals were introduced in numerous molecules like pyrene, [10] quinoline, [11] 1,2,4-triazole, [12] calixarene [13] or ferrocene [14] or even in the axial position of tetraphenylporphinatozinc(II) coordinated by p-pyridyl nitronyl nitroxide. In case of excess of oxidant [8] or if the solution is acidic, [2] nitronyln itroxides are converted spontaneously to imino nitroxide in an on-reversiblew ay (Way III), as described in Scheme 1.…”

“…[9] Although imino and nitronyl nitroxide free-radical derivatives are obtained satisfactorily with numerous substituents, the Ullman routes uffers from major drawbacks in the case of highly aromatic aldehydew hich requirem ulti-step synthesis. Their lows olubility in methanol as well as the stabilization of the aldehyde function by resonance prevents the condensation with 6 in an appropriate manner.D espite these constraints, the Ullman radicals were introduced in numerous molecules like pyrene, [10] quinoline, [11] 1,2,4-triazole, [12] calixarene [13] or ferrocene [14] or even in the axial position of tetraphenylporphinatozinc(II) coordinated by p-pyridyl nitronyl nitroxide. [15] Our interest in the phthalocyanine dyes as ap romising group of fluorophore derivatives with highq uantum yield, used in numerous applications( chemical sensor,s olarc ell, PDT, etc.…”

Identification of radiation‐induced radical structure in azocalix[4]arene: an EPR study

“…Calixarenes are important structures. Hence, EPR studies on these structures exist in the literature . The present work is significant in this field because it is difficult to obtain the single crystalline form of calixarene compounds.…”

“…Hence, EPR studies on these structures exist in the literature. [9][10][11] The present work is significant in this field because it is difficult to obtain the single crystalline form of calixarene compounds. In our previous studies, we synthesized polymeric calix[n]arene and the chromogenic azocalix [4]arene derivatives containing amide groups at the lower rim and investigated their selective extraction of transition metal ions.…”