Reversible transformation of single-crystal two-dimensional polymer framework for photo/thermal reversible photolithography

The preparation of large-sized single crystals of two-dimensional covalent organic frameworks (2D COFs) or 2D polymers is already a highly challenging task, and the study of reversible transformations of such materials in their single-crystalline state remains an unexplored research area. Herein, we demonstrate a successful photo/thermal reversible transformation between a 2D polymer framework and its monomer while maintaining single-crystal integrity. By photopolymerization under UV light and thermal depolymerization at elevated temperatures, repeatable structural transitions were achieved in a single-crystal state. Leveraging this reversible behavior, a thin-film material with rewritable photolithographic properties was developed. Patterns could be inscribed using UV light and erased or modified through heating, showing excellent reversibility. These findings deepen the understanding of reversible covalent bond transformations and underscore their potential applications in photolithography and advanced manufacturing technologies.