Carbazole-Based Colorimetric Anion Sensors

Abstract

Owing to their strong carbazole chromophore and fluorophore, as well as to their powerful and convergent hydrogen bond donors, 1,8-diaminocarbazoles are amongst the most attractive and synthetically versatile building blocks for the construction of anion receptors, sensors, and transporters. Aiming to develop carbazole-based colorimetric anion sensors, herein we describe the synthesis of 1,8-diaminocarbazoles substituted with strongly electron-withdrawing substituents, i.e., 3,6-dicyano and 3,6-dinitro. Both of these precursors were subsequently converted into model diamide receptors. Anion binding studies revealed that the new receptors exhibited significantly enhanced anion affinities, but also significantly increased acidities. We also found that rear substitution of 1,8-diamidocarbazole with two nitro groups shifted its absorption spectrum into the visible region and converted the receptor into a colorimetric anion sensor. The new sensor displayed vivid color and fluorescence changes upon addition of basic anions in wet dimethyl sulfoxide, but it was poorly selective; because of its enhanced acidity, the dominant receptor-anion interaction for most anions was proton transfer and, accordingly, similar changes in color were observed for all basic anions. The highly acidic and strongly binding receptors developed in this study may be applicable in organocatalysis or in pH-switchable anion transport through lipophilic membranes.

Highly Transparent, Colorless Optical Film with Outstanding Mechanical Strength and Folding Reliability Using Mismatched Charge‐Transfer Complex Intensification

“…As a Li cation approaches two amide groups that are connected by hydrogen bonding, they break the existing hydrogen bonds and interact with the free non‐hydrogen‐bonded oxygen atoms in CO, as shown in Figure S10 of the Supporting Information. Because the interaction between Li cation and CO is stronger than that between NH and CO, [ 60,105 ] the CO peak in the FT‐IR spectra shifts to a lower wavenumber. In addition, complexation between Li cation and CO results in a new interaction between the free protons in NH and Cl anion.…”

Dissecting transmembrane bicarbonate transport by 1,8-di(thio)amidocarbazoles

“…[6][7][8] Chloride transporters have been also shown to display promising antibacterial activity, notably against antibiotic resistant bacteria. 9,10 Diamides and dithioamides based on the carbazole skeleton are known for their high oxyanion affinity, 11 outstanding optical properties 12,13 and ability to transport various biologically relevant anions, such as chloride, 11,14,15 organic phosphates, 16 aspirin, 16 and amino acids across lipid bilayers. 17 Owing to their modular synthesis, high anion transport activity, and good deliverability, these compounds are promising candidates for medicinal applications.…”

Fused aza-heterocyclic ligands: expanding the MOF chemist's toolbox

“…This expanded range of possible bridging angles has been well used in carbazoles, for example, to give both MOF ligands and anionophores. 21…”