Exfoliation of Molecular Crystals Enables Two-Dimensional Polymerization for Stable Photoelectric Response Devices

Abstract

Two-dimensional polymers (2DPs) have emerged as a class of important materials with the unique advantages of an ultrathin, lightweight nature and a large accessible surface area, showing their promising potential in the area of optoelectronics, energy storage and conversion, and molecular separation. Currently, their synthetic routes mainly rely on two approaches: polymerization coupled with assembly of building blocks, or solid-state crosslinking within preassembled crystals. Herein, we developed a 2D polymerization strategy based on exfoliated 2D molecular crystals (2DMCs), in which crosslinking within individual 2DMCs covalently locks the arrangement of preassembled 2D architecture while maintaining the exfoliated 2D morphology. The monomer is designed with a structure of π-extended rigid cores and multiarm siloxane reactive sites, yielding crystals with lamellar structure. These crystals can be exfoliated into free-standing, well-dispersed 2DMCs with a thickness of 2.2–8.8 nm, and subsequent solid-state crosslinking maintains the 2DMCs into stable 2D architectures, affording organic–inorganic hybrid 2DPs. This process covalently locks their in-plane preassembled structure with long-range π–π stacking, thereby enabling the resulting 2DPs to preserve superstructure-derived functions while exhibiting improved performance and enhanced stability. This work presents a design concept for 2DP synthesis from exfoliated 2DMCs, demonstrating the construction of 2D polymer networks according to preassembled architecture.