Proton-Triggered Fluorescence Switching in Self-Exfoliated Ionic Covalent Organic Nanosheets for Applications in Selective Detection of Anions

The
exfoliation of covalent organic frameworks into covalent organic nanosheets
(CONs) not only helps to reduce fluorescence turn-off phenomena but
also provides well-exposed active sites for fast response and recovery
for various applications. The present work is an example of rational
designing of a structure constructed by condensing triaminoguanidinium
chloride (TGCl), an intrinsic ionic linker, with a fluorophore,
2, 5-dimethoxyterephthalaldehyde (DA), to produce highly fluorescent
self-exfoliable ionic CONs (DATGCl-iCONs). These fluorescent
iCONs are able to sense fluoride ions selectively down to the ppb
level via the fluorescence turn-off mechanism. A closer look at the
quenching mechanism via NMR, zeta potential measurement, lifetime
measurement, and density functional theory calculations reveals unique
proton-triggered fluorescence switching behavior of newly synthesized
DATGCl-iCONs.