Synthesis of Pyrene-Based Two-Dimensional Polymer Film by Gas-Liquid Interface Strategy

Two-dimensional (2D) material, such as 2D polymer (2DP) and 2D covalent organic framework (2D-COF), has arisen as promising materials because of their unique physicochemical properties and great potential in optoelectronics, sensing, catalysis, separation, and energy storage and conversion. The preparation of 2DP films with desirable structures is promising but remains a significant challenge. Recently, vigorous efforts have been devoted to synthesizing 2DP films through different methods, such as interfacial synthesis at gas-water or liquid-liquid. Herein, a fluorescent pyrene-based 2D polyimine (2D-PI) thin film was prepared via Schiff-base condensation between 4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl)tetraaniline and 2,5-dihydroxyterephthalaldehyde with trifluoromethanesulfonic acid as a catalyst at room temperature by a surfactant-monolayer-assisted interfacial synthesis (SMAIS) approach. The morphology, structure, crystallinity, and fluorescence intensity of the film were characterized by scanning electron microscopy, atomic force microscopy, transmission electron microscopy, X-ray diffraction, fluorescence spectroscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy. The results revealed that the film thickness was 70 nm, which could be controlled by changing the monomer concentration. The imine bond formation was confirmed by Fourier transform infrared spectroscopy and Raman spectroscopy. The film crystallinity depended on the diffusion rate of monomer and was significantly improved by adding trifluoromethanesulfonic acid and surfactant monolayer, which provided a confined 2D template for polymerization. In addition, the fluorescence strength of the film was enhanced by the existence of intramolecular hydrogen bonding in the framework structure. This study provided a unique idea for the preparation of 2DP films with solid luminescent properties, which may be potentially applied to detect water content in organic solvent.