Fluorinated 2D conjugated porous organic polymer films with modular structural topology for controlled molecular sieving

Abstract

Two-dimensional conjugated porous organic polymers (2D CPOPs) exhibit excellent structural tunability and stability in organic solvents, making them suitable for controlled nanofiltration applications. We report the fabrication of free-standing, flexible films of adaptable thickness and surface areas through a facile drop-cast approach using four novel fluorinated imine-linked 2D CPOPs. The resulting structures exhibit various pore sizes (2.6–3.2 nm), structural topologies (homopore and heteropore topologies), and skeletal backbone functionalities (with and without fluorine). The films comprise tightly packed layered sheets, which are easily exfoliated into nanometer-thick sheets with large lateral domains. The properties of the films, such as hydrophobicity, flexibility, hardness, porosity, thermal stability, morphology, and anisotropic properties of the films are evaluated. The films exhibit controlled nanofiltration performance that can be tuned by tailoring the pore architectures in terms of pore size, pore functionality, and structural topology. Particularly for the heteropore structure, the larger pores control the molecular weight cutoff (MWCO) while allowing the solvent molecules to pass through, whereas the smaller pores only act as channels for solvent transport. We report the experimental and theoretical observations of these structures, providing new insights into the fundamental understanding of molecular transportation through materials with multiple pore sizes.