Nanosheet-Assembled Zirconium-Porphyrin Frameworks Enabling Surface-Confined, Initiator-Free Photosynthesis of Ultrahigh Molecular Weight Polymers.

Abstract

Metal-organic frameworks with well-organized low-dimensional architectures provide significant thermodynamic and/or kinetic benefits for diverse applications. We present here the controlled synthesis of a novel class of hierarchical zirconium-porphyrin frameworks (ZrPHPs) with nanosheet-assembled hexagonal prism morphology. The crystal growth behaviors and structural evolution of ZrPHPs in an additive-modulated solvothermal synthesis are examined, showing an "assembly-hydrolysis-reassembly" mechanism towards the formation of 2D nanosheets with ordered arrangement. Because of the highly-accessible active sites harvesting broadband photons, ZrPHPs serve as adaptable photocatalysts to regulate macromolecular synthesis under full-range visible light and natural sunlight. An initiator-free, oxygen-tolerant photopolymerization system is established, following a distinctive mechanism involving direct photo-induced electron transfer to dormant species and hole-mediated reversible deactivation. Specifically, ZrPHPs provide a surface-confined effect towards the propagating chains which inhibits their recombination termination, enabling the highly-efficient synthesis of ultrahigh molecular weight polymers (Mn >1,500,000) with relatively low dispersity (Đ≈1.5).