Artificial chloride transporters have been intensely investigated in view of their potential medicinal applications. Recently, we have established 1,8-diamidocarbazoles as a versatile platform for the development of active chloride carriers. In the present contribution, we investigate the influence of various electron-withdrawing substituents in positions 3 and 6 of the carbazole core on the chloride transport activity of these anionophores. Using lucigenin assay and large unilamellar vesicles as models, the 3,6-dicyano- and 3,6-dinitro- substituted receptors were found to be highly active and perfectly deliverable chloride transporters, with EC50,270s value as low as 22 nM for the Cl−/NO3− exchange. Mechanistic studies revealed that diamidocarbazoles form 1:1 complexes with chloride in lipid bilayers and facilitate chloride/nitrate exchange by carrier mechanism. Furthermore, owing to its increased acidity, the 3,6-dinitro- substituted receptor acts as a pH-switchable transporter, with physiologically relevant apparent pKa of 6.4.

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.

Endowed with strong carbazole chromophore and fluorophore as well as with 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 at the development of carbazole-based colorimetric anion sensors, we describe here the synthesis of 1,8-diaminocarbazoles substituted with strongly electron-withdrawing substituents: 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 show greatly enhanced anion affinity, but also significantly increased acidity. We found also that rear substitution of 1,8-diamidocarbazole with two nitro groups shifts its absorption spectrum to the visible region and converts receptor into colorimetric anion sensor. The new sensor produces vivid changes in colour and fluorescence upon addition of basic anions in wet DMSO, but is poorly selective: due to its greatly enhanced acidity, for most anions the dominant receptor-anion interaction is proton transfer and, accordingly, similar changes in colour can be observed for every basic anion. The highly acidic and strongly binding receptors developed in this study may find applications in organocatalysis or in pH-switchable anion transport through lipophilic membranes.

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Endowed with strong carbazole chromophore and fluorophore as well as with 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 at the development of carbazole-based colorimetric anion sensors, we describe here the synthesis of 1,8-diaminocarbazoles substituted with strongly electron-withdrawing substituents: 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 show greatly enhanced anion affinity, but also significantly increased acidity. We found also that rear substitution of 1,8-diamidocarbazole with two nitro groups shifts its absorption spectrum to the visible region and converts receptor into colorimetric anion sensor. The new sensor produces vivid changes in colour and fluorescence upon addition of basic anions in wet DMSO, but is poorly selective: due to its greatly enhanced acidity, for most anions the dominant receptor-anion interaction is proton transfer and, accordingly, similar changes in colour can be observed for every basic anion. The highly acidic and strongly binding receptors developed in this study may find applications in organocatalysis or in pH-switchable anion transport through lipophilic membranes.