Two new chemically stable [acid and base] 2D crystalline covalent organic frameworks (COFs) (TpPa-1 and TpPa-2) were synthesized using combined reversible and irreversible organic reactions. Syntheses of these COFs were done by the Schiff base reactions of 1,3,5-triformylphloroglucinol (Tp) with p-phenylenediamine (Pa-1) and 2,5-dimethyl-p-phenylenediamine (Pa-2), respectively, in 1:1 mesitylene/dioxane. The expected enol-imine (OH) form underwent irreversible proton tautomerism, and only the keto-enamine form was observed. Because of the irreversible nature of the total reaction and the absence of an imine bond in the system, TpPa-1 and TpPa-2 showed strong resistance toward acid (9 N HCl) and boiling water. Moreover, TpPa-2 showed exceptional stability in base (9 N NaOH) as well.
A luminescent
Zr(IV)-based metal–organic framework (MOF),
with the underlying fcu topology, encompassing a π-conjugated
organic ligand with a thiadiazole functionality, exhibits an unprecedented
low detection limit of 66 nM for amines in aqueous solution. Markedly,
this ultralow detection is driven by hydrogen-bonding interactions
between the linker and the hosted amines. This observation is supported
by density functional theory (DFT) calculations, which clearly corroborate
the suppression of the twisting motion of thiadiazole core in the
presence of amine, reducing significantly the nonradiative recombination
pathways and subsequently enhancing the emission intensity. Credibly,
nicotine regarded as a harmful chemical and bearing an amine pending
group is also detected with high sensitivity, positioning this MOF
as a potential sensor for practical environmental applications. This
finding serves also as a benchmark to understand the sensing mechanism
in MOFs.
A media for inkless and erasable printing has been developed using photochromic MOFs. Different coloured printing has been achieved by varying the structure of the MOF. The resultant printing has a good resolution and stability, is capable of being read both by human eyes and smart electronic devices and the paper can be reused for several cycles without any significant loss in intensity.
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