Redox polymers incorporating pendant 6‐oxoverdazyl and nitronyl nitroxide radicals

Abstract

Polymers comprised of redox-active organic radicals have emerged as promising materials for use in a variety of organic electronics, including fast-charging batteries. Despite these advances, relatively little attention has been focused on the diversification of the families of radicals that are commonly incorporated into polymer frameworks, with most radical polymers being comprised of nitroxide radicals. Here, we report two new examples prepared via ring-opening methathesis polymerization containing 6-oxoverdazyl and nitronyl nitroxide radicals appended to their backbones. The polymerization reaction and optoelectronic properties were explored in detail, revealing high radical content and redox activity that may be advantageous for their use as semiconducting thin films. Initial studies revealed that current-voltage curves obtained from thin films of the title polymers exhibited memory effects making them excellent candidates for use in resistive memory applications.Given the rejuvenated interest in the study of radical polymers as semiconducting materials and the promise of examples exhibiting ambipolar redox properties in a variety of applications, we report the synthesis, characterization, and thin-film properties of two new polymers prepared using a radical-tolerant ring-opening metathesis polymerization (ROMP) reaction. Such structural elaboration is essential for further progression of the stable radical polymer research field and the applications it targets.Additional supporting information may be found in the online version of this article. † These authors contributed equally.

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

“…Whereas highly different first reduction potentials were observed for the five NN biradicals, covering a range of more than 370 mV, the first oxidation potentials of the nitronyl nitroxides are very similar (Table S2). As oxidation potentials between 330 and 520 mV are typically observed for NNs in literature, the first oxidation process can be ascribed to the formation of an oxammonium cation from the respective (bi)­radical. ,,,,,, This is further corroborated by analogous CV and DPV studies of the silylated precursors (Figures S29 and S30 and Table S1), which reveal a similar redox behavior as observed for the respective nitronyl nitroxides, but the pronounced oxidation event at 366–422 mV (all potentials vs Fc 0/+ ), being observed for all NN, is absent in PBI–Si, IIn–Si, and PhDPP–Si. Electron-rich ThDPP–Si and FuDPP–Si exhibit an additional oxidation process between 300 and 400 mV (Figure S30), which can be ascribed to the DPP chromophore oxidation, although these processes occur at slightly higher potentials (500 mV) in the unsubstituted parent chromophore due to the smaller π-system.…”

“…In contrast to the oxidation process, reduction potentials of NNs are hardly reported in literature and are thus much less indicative. For instance, reduction potentials between −1270 and −1330 mV have been reported for NN-containing redox polymers or fused thiophene systems, , however, these reduction potentials strongly depend on the π-system. Accordingly, it can be concluded that the electron accepting properties (reduction) are strongly driven by the chromophore core and reflect its electron affinity, whereas the first oxidation potential is determined by the nitronyl nitroxide radical moiety.…”

“…Silica−gel column chromatography was performed on silica gel (particle size of 0.040−0.063 mm) with freshly distilled solvents. 1 H NMR and 13 C{ 1 H} NMR spectra were recorded on a Bruker Avance III HD 400 spectrometer at 298 K. Chemical shift data are reported in parts per million (ppm, δ scale) downfield (for positive shifts) or upfield (for negative shifts) from tetramethylsilane and referenced internally to the residual proton (for proton NMR) in the solvent (CDCl 3 , δ = 7.26; CD 2 Cl 2 , δ = 5.32) or to the carbon resonance (CDCl 3 , δ = 77.16; CD 2 Cl 2 , δ = 53.84). The coupling constants are listed in Hertz and multiplicities abbreviated as follows: s = singlet, d = doublet, t = triplet, q = quartet, m = multiplet, vt = virtual, br = broad.…”

“…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.…”

All-in-One Step from a Radical Monomer: Vacuum Synthesis of Electroswitchable Radical Polymer Thin Films by Solvent-Free Surface Polymerization

“…The excellent smoothness of the deposits demonstrated in Figure 1e is also consistent with the very low roughness and high uniformity exhibited by 6-oxoverdazyl polyradicals synthesized by wet chemistry. 6,32 Matrix-assisted laser desorption and ionization (MALDI) mass spectrometry was used to confirm the Grubbs-III-assisted surface polymerization of N-6OV to produce a PN-6OV. MALDI is an effective tool for the detection of polymers in deposits with minimal fragmentation.…”