Radicals are inevitable intermediates during the charging and discharging of organic redox electrodes. The increase of the reactivity of the radical intermediates is desirable to maximize the capacity and enhance the rate capability but is detrimental to cycling stability. Therefore, it is a great challenge to controllably balance the redox reactivity and stability of radical intermediates to optimize the electrochemical properties with a good combination of high specific capacity, excellent rate capability, and long-term cycle life. Herein, we reported the redox and tunable stability of radical intermediates in covalent organic frameworks (COFs) considered as high capacity and stable anode for sodium-ion batteries. The comprehensive characterizations combined with theoretical simulation confirmed that the redox of C−O• and α-C radical intermediates play an important role in the sodiation/desodiation process. Specifically, the stacking behavior could be feasibly tuned by the thickness of 2D COFs, essentially determining the redox reactivity and stability of the α-C radical intermediates and their contributive capacity. The modulation of reversible redox chemistry and stabilization mechanism of radical intermediates in COFs offers a novel entry to design novel high performance organic electrode materials for energy storage and conversion.

Reported is the synthesis, characterization, and material properties of the first π-conjugated two-dimensional covalent organic radical framework (CORF), PTM-CORF, based on the stable polychlorotriphenylmethyl (PTM) radical. The covalent organic framework (COF) precursor (PTM-H-COF) was first synthesized by liquid/liquid interfacial acetylenic homocoupling of a triethynylpolychlorotriphenylmethane monomer, and showed crystalline features with a hexagonal diffraction pattern matching that of A-B-C stacking. Subsequent deprotonation and oxidation of the PTM units in PTM-H-COF gave PTM-CORF. Magnetic measurements revealed that the neighboring PTM radicals in the PTM-CORF are anti-ferromagnetically coupled each other, with a moderate exchange interaction (J=-375 cm ). The PTM-CORF has a small energy gap (ca. 0.88 eV) and a low-lying LUMO energy level (-4.72 eV), and exhibits high electrocatalytic activity and durability toward the oxygen reduction reaction.

It is a challenge to prepare organic electrodes for sodium-ion batteries with long cycle life and high capacity. The highly reactive radical intermediates generated during the sodiation/desodiation process could be a critical issue because of undesired side reactions. Here we present durable electrodes with a stabilized α-C radical intermediate. Through the resonance effect as well as steric effects, the excessive reactivity of the unpaired electron is successfully suppressed, thus developing an electrode with stable cycling for over 2,000 cycles with 96.8% capacity retention. In addition, the α-radical demonstrates reversible transformation between three states: C=C; α-C·radical; and α-C− anion. Such transformation provides additional Na+ storage equal to more than 0.83 Na+ insertion per α-C radical for the electrodes. The strategy of intermediate radical stabilization could be enlightening in the design of organic electrodes with enhanced cycling life and energy storage capability.

A consolidated ionothermal strategy was developed for the polymerization of thermally unstable nitriles to construct high performance materials with permanent porosity, and carbazole, dibenzofuran, and dibenzothiophene were separately introduced into covalent triazine-based networks to investigate the effects of heterocycles on the gas adsorption performance. Three nitriles, namely 3,6-dicyanocarbazole, 3,6-dicyanodibenzofuran, and 3,6-dicyanodibenzothiophene, were designed and synthesized, which were readily converted to heat-resistant intermediates at a moderate temperature and then polymerized to create highly porous poly(triazine) networks instead of the traditional one-step procedure. This documents an improved strategy for the successful construction of heterocyclic-functional triazine-based materials. The chemical structures of monomers and polymers were confirmed by 1 H NMR, FTIR, and elemental analysis. Such polymers with high physical−chemical stability and comparable BET surface areas can uptake 1.44 wt % H 2 at 77 K/1 bar and 14.0 wt % CO 2 at 273 K/1 bar and present a high selectivity for gas adsorption of CO 2 (CO 2 /N 2 ideal selectivity up to 45 at 273K/1.0 bar). The nitrogen-and oxygen-rich characteristics of carbazole and dibenzofuran feature the networks strong affinity for CO 2 and thereby high CO 2 adsorption capacity. This also helps to thoroughly understand the influence of pore structure and chemical composition on the adsorption properties of small gas molecules.

Peri-acenes are good model compounds for zigzag graphene nanoribbons, but their synthesis is extremely challenging owing to their intrinsic open-shell diradical character. Now, the successful synthesis and isolation of a stable peri-tetracene derivative PT-2ClPh is reported; four 2,6-dichlorophenyl groups are attached onto the most reactive sites along the zigzag edges. The structure was confirmed by X-ray crystallographic analysis and its electronic properties were systematically investigated by both experiments and theoretical calculations. It exhibits an open-shell singlet ground state with a moderate diradical character (y =51.5 % by calculation) and a small singlet-triplet gap (ΔE =-2.5 kcal mol by SQUID measurement). It displays global aromatic character, which is different from the smaller-size bisanthene analogue BA-CF3.

A series of microporous imide functionalized 1,3,5-triazine frameworks (named TPIs@IC) were designed by a easy-construction technology other than the known imidazation method for the construction of porous triazine-based polyimide networks (TPIs) with same chemical compositions. In contrast to TPIs, TPIs@IC exhibit much higher Brunauer-Emmett-Teller (BET) surface areas (up to 1053 m 2 g -1 ) and 10 carbon dioxide uptake (up to 3.2 mmol g -1 /14.2 wt% at 273K/1bar). The presence of abundant ultramicropores at 5.4~6.8 Å, mainly ascribed to a high-level cyano cross-linking, allows high heat absorption and high selective capture of CO 2 . The Q st (CO 2 esoteric enthalpies) from their CO 2 adsorptions isotherms at 273 and 298 K are calculated to be in the range 46.1-49.3 kJ mol -1 at low CO 2 loading, and ideal CO 2 /N 2 separation factors are up to 151, exceeding those of most reported porous 15 organic polymers to date. High storage capacities of TPIs@IC for other small gases like CH 4 (5.01 wt% at 298 K/22 bar) and H 2 (1.47 wt% at 77K/1bar) were also observed, making them promising adsorbents for gas adsorption and separation. This paper presents a facile and efficient method for the construction of microporous imide functionalized 1,3,5-triazine frameworks (ITFs), which exhibit high sorption capacities of CO 2 , CH 4 and H 2 , showing potentials in small gas separation and recovery.

Ethyl acetate-appended nanoporous organic polytriazine (NOP-20 ) displays a high CO2–N2 ideal selectivity of 81 (273 K), which makes it a promising candidate as adsorbent for CO2 capture in fields related to the environment and energy.

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