Intramolecular Charge Transfer‐Regulated Isomeric Covalent Organic Frameworks for Multiple Solvent‐Response

Stimulus-responsive covalent organic frameworks (COFs) own color-switching characteristics when exposed to external stimuli. However, the investigations on the multiple solvent-responsive COFs remain a challenge due to the synthetic difficulties and uncontrollable charge transfer process toward various solvents. In this contribution, two novel isomeric COFs with a regulated intramolecular charge transfer (ICT) process by modulating the distance between the donor/acceptor and the linkage are synthesized. The as-prepared two isomeric COFs exhibited significantly distinct solvatochromic behaviors in water, acid, and halogenated solvents, respectively. These multiple solvent-responsive functions are attributed to the various enhancement degrees of the ICT process by the hydrogen bond interactions, protonation interactions, and halogen/π interactions, respectively. In addition, the two isomeric COFs are employed as stimulation-responsive powder or ink, displaying excellent image and data encryption performances. The work can not only offer a novel viewpoint for the creation of multiple solvent-responsive COFs but also expand the COFs' potential applications in information encryption and anti-counterfeiting.