Transformation between 2D and 3D Covalent Organic Frameworks via Reversible [2 + 2] Cycloaddition
Thaksen Jadhav, Yuan Fang, Chenghao Liu, Afshin Dadvand, Ehsan Hamzehpoor, W. J. Patterson, Antranik Jonderian, Robin S. Stein, Dmitrii F. Perepichka
Abstract
We report the first transformation between crystalline vinylene-linked two-dimensional (2D) polymers and crystalline cyclobutane-linked three-dimensional (3D) polymers. Specifically, absorption-edge irradiation of the 2D poly(arylenevinylene) covalent organic frameworks (COFs) results in topological [2 + 2] cycloaddition cross-linking of the π-stacked layers in 3D COFs. The reaction is reversible, and heating to 200 °C leads to a cycloreversion while retaining the COF crystallinity. The resulting difference in connectivity is manifested in the change of mechanical and electronic properties, including exfoliation, blue-shifted UV–vis absorption, altered luminescence, modified band structure, and different acid-doping behavior. The Li-impregnated 2D and 3D COFs show a significant room-temperature ion conductivity of 1.8 × 10–4 S/cm and 3.5 × 10–5 S/cm, respectively. Even higher room-temperature proton conductivity of 1.7 × 10–2 S/cm and 2.2 × 10–3 S/cm was found for H2SO4-treated 2D and 3D COFs, respectively.