Nitroxide-Substituted Nitronyl Nitroxide and Iminonitroxide

Abstract

We report on the highly compact nitroxide-substituted nitronyl nitroxide 1 and iminonitroxide 2; they have isoelectronic structures with trimethylenemethane. These diradicals are stable under aerated conditions at room temperature and have large positive exchange interactions: J/k(B) = +390 K (H = -2JS(1)(/)(2)·S(1/2)) for 1 and J/k(B) ≈ +550 K for 2.

Triplet Diradical‐Cation Salts Consisting of the Phenothiazine Radical Cation and a Nitronyl Nitroxide

“…As shown in Figure 6b,t he calculated spin densities of (DAA-PTZ) + + -NN spread across the whole molecule and tightly combine, thereby providing al arge spin-polarization effect. [8][9][10] We then carried out theoretical calculations (Gaussian 09 [19] and ORCA program package [20] ). Structuralo ptimization was achieveda tt he UB3LYP/6-31G* level of theory by using the polarizablec ontinuumm odel (PCM) methodw ithb utyronitrile as the solvent, and the magnetic tensors were calculated at the UBLYP/Sapporo-DZP level by using the COSMO method with acetonitrile as the solvent: g xx-calcd = 2.0075, g yy-calcd = 2.0027, g zz-calcd = 2.0055, g ave-calcd = 2.0052, j D calcd /hc j = 0.0056 cm À1 ,a nd j E calcd /hc j = 0.0003 cm À1 (see Tables S2-S5 in the Supporting Information).…”

“…The experimentally determinedi ntramolecular ferromagnetic interaction of J 1 /k B =+320 Ki sr easonable when compared with the results of our previous studies on radical-substituted radicalc ations [8,9] and other diradical studies. [10] The origin of the strong intramolecular ferromagnetic interactions is considered to derive from the delocalization of the spin densities. The two molecularo rbitals of the unpaired electrons in the triplet state (singlyo ccupied molecular orbitals,S OMOs) are distributed on either the (DAA-PTZ) + + or NN site (see Figure S8), which results in the tight combination of the spin densities on the (DAA-PTZ) + + and NN sites (Figure6b).T his is a commonf eature of tripletdiradicals at room temperature.…”

“…[6] Of particular interest is the creation of stable radical-substitutedr adical-cation systems with large positive intramolecular exchange interactions between the radicala nd the radical cation.O nlyafew such compounds have been reported to date, because diradical speciesi na small space are generally unstable under ambient conditions. [7][8][9][10] In the course of our challenging research program, we have shown that nitronyl nitroxide (NN) substituted dihydrophenazine [8] and trioxytriphenylamine radicalc ations [9] are stable tripletd iradical cations with large exchange interactions [8,9] that exhibit magnetic phase transitions at low temperature.R ecently,w ef ound that the NN-ter(ethylenedioxythiophene)d iradical cation is ab orderline case of isolable stability. [11] Although the magnetic properties of this species could not be investigatedi nd etail because of its slow decomposition, EPR and UV/Vis analyses of the isolated species clearly indicatedt he formation of the NN-ter(ethylenedioxythiophene) diradical cation.…”

Structural Factors Controlling the Spin–Spin Exchange Coupling: EPR Spectroscopic Studies of Highly Asymmetric Trityl–Nitroxide Biradicals

“…10–12 Several factors such as nature of the linkers between two spins, conformations, substituents and environment (e.g., temperature, solvent, etc) control the exchange coupling magnitude in biradicals. 27 Through conformational constraint into the co-planarity of two radical moieties with m-phenylene 10,28,29 or simple direct linkage, 30 stable trimethylenemethane (TMM)-type biradicals with large positive exchange interactions have been recently obtained which show great potential as building blocks for robust magnetic materials. In contrast, biradicals with rigid geometries holding two nitroxide moieties approximately orthogonal to one another have weak exchange coupling but show enhanced DNP properties.…”

Substitution effects on optical properties of iminonitroxide- substituted iminonitroxide diradical

“…They have also shown a sharp emission band of [Eu(hfac) 3 IN] centred at 615 nm upon excitation with 212 nm light [22] (see some books [23,24] for details). Recently, Hasegawa also found that some organic diradicals composed of two radical groups bridged with a methylene group such as iminonitroxide-substituted iminonitroxide, referred to as IN-IN hereafter, first synthesised by Suzuki et al [25,26], being coexistent with Eu or Tb ion show highly efficient lanthanide-ion-specific photoemission [27]. Suzuki et al also synthesised Cu complexes with the similar kind of diradical ligands [28].…”