Monolayer-Assisted Surface-Initiated Schiff-Base-Mediated Aldol Polycondensation for the Synthesis of Crystalline sp2 Carbon- Conjugated Covalent Organic Framework Thin Films

sp2 carbon-conjugated covalent organic frameworks (sp2c-COFs) with superb in-plane pi-conjugations, high chemical stability, and robust framework structure are expected to be ideal films/membranes for a wide range of applications including energy-related devices and optoelectronics. However, so far, sp2c-COFs have been mainly limited to microcrystalline powders, and this consequently hampered their performances in devices. Herein, we report a simple and robust methodology to fabricate large-area, free-standing, and crystalline sp2c-COF films (TFPT-TMT and TB-TMT) on various solid substrates (e.g., fluorine-doped tin oxide, aluminum sheet, polyacrylonitrile membrane) by self assembly monolayer-assisted surface-initiated Schiff-base-mediated aldol polycondensation (namely, SI-SBMAP). The resultant sp2c-COF films show lateral sizes up to 120 cm2 and tunable thickness from tens of nanometers to a few micrometers. Owing to the robust framework and highly ordered quasi-1D channels, the sp2c-COF membrane-based osmotic power generator presents an output power density of 14.1 W m-2 under harsh conditions, outperforming most reported COF membranes as well as commercialized benchmark devices (5 W m-2). This work demonstrates a simple and robust interfacial methodology for the fabrication of sp2c-COF films/membranes for green energy applications and potential optoelectronics.

Automated summary

We successfully fabricated large-area, free-standing, and crystalline sp2c-COF films (TFPT-TMT and TB-TMT) on various solid substrates by self assembly monolayer-assisted surface-initiated Schiff-base-mediated aldol polycondensation. The fabricated sp2c-COF films have tunable thickness and lateral size up to 120 cm2. The sp2c-COF membrane-based osmotic power generator demonstrated an output power density of 14.1 W m-2 under harsh conditions, outperforming most reported COF membranes and commercialized benchmark devices (5 W m-2).