Site-Memory-Triggered Reversible Acronym Encryption in a Nitrogen-Rich Pore-Partitioned MOF for Ultrasensitive Monitoring of Roxarsone and Dichloran over Multiple Platform

Stimuli-responsive emission color
modulation in fluorescent metal–organic
frameworks (MOFs) promises luminescence-ink-based security application,
while task-specific functionality-engineered pores can aid fast-responsive,
discriminative, and ultralow detection of harmful organo-aromatics
in the aqueous phase. Considering practical applicability, a self-calibrated
fluoro-switch between encrypted and decrypted states is best suited
for antiforgery measures, whereas image-based monitoring of organo-toxins
by repetitive and handy methods over multiple platforms endorses in-field
sensory potential. Herein, we constructed a mixed-ligand based chemically
stable and bilayered-pillar MOF from –NH2-hooked
pyridyl linker and tricarboxylate ligand that embraces negatively
charged [Cd3(μ2-OH)(COO)6]
node and shows pore-space-partitioning by nitrogen-rich flanked organic
struts. Owing to the presence of a self-calibrating triazolylamine
moiety-grafted auxiliary linker, this anionic MOF delineates reversible
and multicyclic fluoro-swapping between protonated-encrypted and deprotonated-decrypted
domains in the alternative presence of acid and base. Such pH-triggered,
site-specific luminescence variation is utilized to construct highly
regenerative anticounterfeiting labels for vivid acronym encryption.
The intense fluorescence signature of the material is further harnessed
in extremely selective and quick responsive sensing of harmful feed
additive roxarsone (ROX) and dichloran (DCNA) pesticide in highly
recyclable fashion with significant quenching and nanomolar limits
of detection (ROX: 52 ppb; DCNA: 26.8 ppb). Notably, the ultrasensitive
fluoro-detection of both these organo-toxins is successfully demonstrated
via a handy paper-strip method as well as on the vegetable surface
for real-time monitoring. Comprehensive density functional theory
studies validate the electron transfer mechanism through redistribution
of molecular orbital energy levels by each of the targeted analytes
in this electron-rich framework besides evidencing MOF-analyte supramolecular
interactions.