Amide‐Triazolium‐Appended Anthracenes for Turn‐On Fluorescence Sensing of Anions in Noncompetitive and Competitive Solvents

Solvent Acts as the Referee in a Match-Up Between Charged and Preorganized Receptors

The prevalence of anion-cation contacts in biomolecular recognition under aqueous conditions suggests that ionic interactions should dominate the binding of anions in solvents across both high and low polarities. Investigations of this idea using titrations in low polarity solvents are impaired by interferences from ion pairing that prevent a clear picture of binding. To address this limitation and test the impact of ion-ion interactions across multiple solvents, we quantified chloride binding to a cationic receptor after accounting for ion pairing. In these studies, we created a chelate receptor using aryl-triazole CH donors and a quinolinium unit that directs its cationic methyl inside the binding pocket. In low-polarity dichloromethane, the 1 : 1 complex (log K1 : 1 ~ 7.3) is more stable than neutral chelates, but fortuitously comparable to a preorganized macrocycle (log K1 : 1 ~ 6.9). Polar acetonitrile and DMSO diminish stabilities of the charged receptor (log K1 : 1 ~ 3.7 and 1.9) but surprisingly 100-fold more than the macrocycle. While both receptors lose stability by dielectric screening of electrostatic stability, the cationic receptor also pays additional costs of organization. Thus even though the charged receptor has stronger binding in apolar solvents, the uncharged receptor has more anion affinity in polar solvents.

Crown ether-appended calix[2]triazolium[2]arene as a macrocyclic receptor for the recognition of the H2PO4−anion

We report the synthesis of a crown ether-appended calix[2]triazolium[2]arene receptor that shows excellent selectivity for H₂PO₄⁻and the binding ability and mode of the receptor to H₂PO₄⁻were demonstrated by¹H NMR studies and DFT calculation.

An electron-deficiency-based framework for NIR-II fluorescence probes

Increasing the electron withdrawing ability of substituents in monochlorinated BODIPY could vary the emission from the NIR-I to NIR-II region together with enhanced response rate, indicative of a promising approach for activatable NIR-II probes.

Fluorescent triazolium for sensing fluoride anions in semi-aqueous solution

A new triazolium-based receptor for fluorescent sensing of inorganic fluoride anions in semi-aqueous solution and the solid state was reported.