Carbazole-Based Colorimetric Anion Sensors.

Krystyna Maslowska-Jarzyna,Jakub A Wagner,Michał J Chmielewski,Maria L Korczak

doi:10.3390/molecules26113205

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.

Highlights

Molecules that selectively change their color or fluorescence in the presence of anionic species are highly appealing for applications in various branches of science, industry and medicine [1]
One appealing building block for the development of colorimetric and fluorescent anion sensors is 1,8-diaminocarbazole [10]. It combines several attractive features, such as the presence of a strong carbazole chromophore and fluorophore directly coupled with anion binding sites, a strong hydrogen bond donor, a rigid skeleton that facilitates the preorganization of auxiliary hydrogen bond donors and the ease of synthesis and derivatization
We described the synthesis of two novel building blocks for the construction of anion receptors: 1,8-diamino-3,6-dicyanocarbazole (12) and 1,8-diamino-3,6dinitrocarbazole (16)

Summary

Introduction

Molecules that selectively change their color or fluorescence in the presence of anionic species are highly appealing for applications in various branches of science, industry and medicine [1]. Such changes may be induced by hydrogen bonding interactions with anions, especially in cases where hydrogen bond donors are directly coupled with the receptor’s chromophores or fluorophores [2,3,4,5,6,7]. Diaminocarbazole-based receptors show high affinity towards oxyanions (carboxylates, phosphates, and sulfates) [3,11,12,13,14,15,16,17,18,19,20,21,22,23,24] and some of them are very active anion transporters [22,25,26]

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Results

Conclusion