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 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
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.