Two-dimensionally extended organic high-spin poly(aminium cationic radical)s and their magnetic force microscopic images

Abstract

Purely organic high-spin poly(aminium cationic radical)s of two-dimensionally extended soluble aromatic polyamines P1 and P2 were prepared by the palladium-catalyzed polycondensation of two multifunctional monomers, followed by chemical or electrochemical oxidations. The chemical structures of the precursor polyamines were fully characterized by 1 H-and 13 C nuclear magnetic resonance (NMR), infrared and MALDI-TOF mass spectra (MS). The aminium radical sites of N,N,N¢,N¢-tetraaryl-pphenylenediamines were connected through the m-phenylene ferromagnetic coupler, which satisfies the non-Kekulé -type molecular design. Oxidation of radical sites was facilitated by electron-donating methoxy substituents. The first oxidation potential (E o ¢(1)) of P2 with methoxy substituents, evaluated from the cyclic voltammograms in CH 2 Cl 2 , was 0.69 V (vs Ag/Ag + ), whereas the E o ¢(1) of P1 without electron-donating substituents was 0.78 V. This result was further verified by spectroelectrochemistry measurements. The electrochemically oxidized P2 displayed a more intense low-energy band at ca. 800 nm ascribed to aminium cationic radicals and bications. Chemical oxidation of P1 and P2 with NOPF 6 solubilized with 18-crown-6 in CH 2 Cl 2 gave the corresponding poly(aminium cationic radical)s. The high-spin ground states were confirmed by the temperature dependence of forbidden electron spin resonance (ESR) transition peak intensities, and the average spin quantum number (S) determined by the magnetic curves reached 8.4/2 at low temperatures. Remarkably, when a small amount of trifluoroacetic acid was added, the half-life of polyradicals reached ca. 1 week at room temperature (RT). This result prompted us to observe the single polymer-based molecular and magnetic images by atomic force microscopy and magnetic force microscopy, respectively. The precursor polyamine P1 showed globular-shaped polymer particles with an average vertical distance of 1.43 nm. After chemical oxidation, the vertical distance of P1 definitely decreased, reflecting the improved p-type character of the nitrogen atoms. Moreover, the detection of weak MFM images supported the presence of magnetic spins in the single polymers.

Tröger's Base‐Containing Aromatic Polymers with Unexpected Properties Endowed by the Insertion of Alkyne Spacers

“…Thus, the first oxidation of P4 was caused by the triphenylamine units. The observed potential is consistent with previous reports of similar triphenylamine polymers …”

“…The observed potential is consistent with previous reports of similar triphenylamine polymers. [27][28][29][30] The redox activity of the selected P2 and P4 samples was also investigated by spectroelectrochemistry. When the potential of 1.5 V was applied to the polymer fi lms, their absorption peak intensities gradually decreased ( Figure S5, Supporting Information).…”

Electrochromic Behavior of Donor-Acceptor Polymers Containing Diketopyrrolopyrrole Unit

“…The E ox values suggested that the triphenylamine derivatives are stronger donors than the fluorene unit and that the substitution of the methoxy group at the para-position with respect to the nitrogen atom facilitated the oxidation, whereas the cyano group substitution made it more difficult. This result is consistent with the redox behavior of the reported triphenylamine oligomers and polymers without the DPP unit [29][30][31][32][33]. In contrast, the E red values originating from the DPP unit were not affected by the electron-donating comonomer structures.…”

Creation of persistent charge-transfer interactions in TCNQ polyester

“…[2][3][4][5] For example, the addition of p-type doping reagents, such as tetracyanoethylene, 7,7,8,8-tetracyanoquinodimethane (TCNQ) and their derivatives, to electron-rich polymers produces open-shell polymers because of the charge-transfer (CT) complexation. [6][7][8][9][10] However, a similar approach using the combination of n-type doping reagents and electrondeficient polymers is rare, probably because of the difficulty of preparing precursor polymers, namely electron-deficient conjugated polymers, and the limited chemical stability of the n-doped polymers at room temperature.…”