Aromatic Interlinking of M₄L₄ Lantern Cages into Porous Films by Postsynthetic Electropolymerization

We report the aromatic interlinking of metal–organic cages into porous films on conductive substrates through a postsynthetic electrochemical coupling pathway. A bidentate ligand decorated with an electroactive 9-phenyl-carbazolyl group is synthesized and subsequently coordinated with the paddlewheel clusters of Rh-, Cu-, and Ru-acetates to yield the [4 + 2] lantern cages. Multisweep cyclic voltammetry (CV) is applied to trigger the electropolymerization of these cages via dimerization of the peripheral carbazolyls, which leads to the in situ formation of uniform coatings on diverse current collectors (e.g., ITO glass, Ni foam, Au-decorated Si wafer) on demand. The thickness of the film can be finely tuned in a range of ca. 5–50 nm simply by varying the CV cycles. The resulting polycage products obtained after 10 CV cycles reveal a mesoporous structure with randomly distributed cavities with a diameter of ca. 15–35 nm. The porous films show electrical conductivity with a sheet resistance of as low as ca. 83 Ω on ITO glass and rapid ionic transfer kinetics with a low charge transfer resistance of ca. 40 Ω on Ni foam. These features prominently reduce the overpotentials and accelerate the catalytic kinetics in electrocatalytic water splitting compared to the blenders of the cage monomer and Nafion binder.