Redox‐Induced Modulation of Exchange Interaction in a High‐Spin Ground‐State Diradical/Triradical System

Abstract

A triplet ground‐state diradical molecule, bis(nitronyl nitroxide)‐substituted diphenyldihydrophenazine (1..), that can be converted into a one‐electron oxidized species, 1…+, in the quartet ground state has been developed. Surprisingly, these species, 1.. and 1…+, can be used under ambient conditions because they are reasonably stable under aerobic conditions, even in solution. The temperature‐dependent magnetic susceptibilities reveal that 1.. and 1…+ are in the triplet state, with a weak exchange interaction (J1/kB = +3.1 K) and quartet ground state with a strong exchange interaction (J2/kB = +160 K), respectively. The interconversion between the neutral and one‐electron oxidized species can be realized through electrochemical reactions. Significantly different absorption bands in the near‐IR region newly appeared in the electronic spectra acquired during electrochemical oxidation/reduction.

From Stable Radicals to Thermally Robust High-Spin Diradicals and Triradicals

“…More recently, Okada and his co-workers have rationally designed and synthesized high-spin stable NN-linked electron donors di- and triradical cations, based on diphenyldihydrophenazine (DPP ·+ -NN, 23 – 25 ), , trioxytriphenylamine (TOT ·+ -NN, 26 , and DOTT + -NN, 27 ), , and phenothiazine (PTZ ·+ -NN, 28 ) . These high-spin di- and triradical cations 23 and 25 – 28 have good stability and large intramolecular exchange couplings between the electron-donor moiety and nitronyl nitroxide (Figure ).…”

“…For (b), black solid and red broken lines showed the observed spectrum of the allowed transition in a glassy diethyl phthalate matrix at 200 K (9.438855 GHz) and the simulated spectrum of the quartet species by using g xx = 2.0080, g yy = 2.0040, g zz = 2.0030, g av = 2.0055, | D / hc | = 0.00473 cm –1 , and | E / hc | = 0.00057 cm –1 , respectively. Reproduced with permission from ref . Copyright 2020 Wiley.…”

Nitronyl Nitroxide Bifunctionalized Electron-Poor Chromophores: Synthesis of Stable Dye Biradicals by Lewis Acid Promoted Desilylation

“…Open shell molecules in general as well as high-spin materials in particular are used for spintronics and molecular magnets, and weakly antiferromagnetically coupling materials (i.e., singlet biradicals) are frequently considered as potential Bose–Einstein condensates (BEC). − However, biradicals are prevalent highly reactive compounds and often feature low ambient stability. In this regard, nitronyl nitroxides (NN) are appealing radical centers due to their exceptional high kinetic stability − and, in contrast to approaches based on 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO), provide the possibility of conjugated attachment to π-scaffolds, enabling intramolecular spin coupling. Additionally, NNs are stable in various media and bear potential for applications like redox polymers or diarylethene-based magnetic photoswitches. , In the past, several electron-rich PAHs and π-systems like benzodithiophenes, pyrene, azulene, polyacenes, , and graphene-like nanoribbons , as well as alkyne-based molecular wires have been incorporated as linkers between two nitronyl nitroxide radical centers.…”

Hysteretic Control of Near‐infrared Transparency Using a Liquescent Radical Cation

“…Thed evelopment of materials with hysteresis curves (Figure 1a,r ight), which can be controlled by several properties depending on the forward and backward processes of controllable physical values,i sn ecessary for creation of invisible optical sensors, multi-channel materials used for the processing of information, and high security telecommunications.W ef ocused on materials with hysteretic changes of drastic near-IR transparencyu nder heating and cooling processes.S uch systems will provide practical processes for the transparent/opaque switching of near-IR transparencyw ith sufficiently wide working temperature ranges.O pen-shell p-electronic molecules are one of suitable candidates for the motifs of the temperature-dependent control of near-IR, because they potentially exhibit dynamic changes in near-IR absorption during association/dissociation processes. [10][11][12] In this study, the solid-liquid phase transitions of dihydrophenazine radical cations [13] bearing ionic liquid properties were utilized to achieve the temperature-dependent hysteretic control of near-IR absorption. Consequently, 1C + •NTf 2 À (NTf 2 À :b is(trifluoromethanesulfonyl)imide anion) was found to exhibit hysteretic phase transitions over aw ide-temperature range with drastic changes in the near-IR transparencyu nder neat and ambient conditions without changes in visible color (Figure 1b,c).…”