Enhanced Crystallinity of Covalent Organic Frameworks Formed Under Physical Confinement by Exfoliated Graphene

• Published in: Small (Weinheim an der Bergstrasse, Germany) Vol. 18; no. 46; pp. e2204152 - n/a
• Main Authors: Roys, Joshua S., O'Brien, Jennifer M., Stucchi, Nicholas D., Raj, Gaurav, Hill, Adam D., Ye, Jingyun, Brown, Ryan D.
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01.11.2022
• Subjects: 2D confinement; computational chemistry; Confinement; Covalence; covalent organic frameworks; Crystallinity; Crystallization; Degree of crystallinity; Density functional theory; Domains; Flakes; Fourier transforms; Graphene; infrared spectroscopy; Mica; Micrometers; Nanotechnology; scanning probe microscopy
• ISSN: 1613-6810; 1613-6829
• DOI: 10.1002/smll.202204152

The polymerization of 1,4‐benzenediboronic acid (BDBA) on mica to form a covalent organic framework (COF‐1) reveals a dramatic increase in crystallinity when physically confined by exfoliated graphene. COF‐1 domains formed under graphene confinement are highly geometric in shape and on the order of square micrometers in size, while outside of the exfoliated flakes, the COF‐1 does not exhibit long‐range mesoscale structural order, according to atomic force microscopy imaging. Micro‐Fourier transform infrared spectroscopy confirms the presence of COF‐1 both outside and underneath the exfoliated graphene flakes, and density functional theory calculations predict that higher mobility and self‐assembly are not causes of this higher degree of crystallinity for the confined COF‐1 domains. The most likely origin of the confined COF‐1's substantial increase in crystallinity is from enhanced dynamic covalent crystallization due to the water confined beneath the graphene flake. Confinement of covalent organic framework (COF‐1) precursors at the solid–solid mica–graphene interface dramatically enhances COF crystal growth compared to the unconfined reaction. The enhanced crystallinity originates from water trapped by graphene capping layers during the COF‐1 condensation reaction, promoting defect correction and recrystallization via dynamic covalent crystallization.