Colourimetric Carboxylate Anion Sensors Derived from Viologen‐Based Receptors

Abstract

A series of tri- and tetrapodal viologen-based anion receptors showing a colourimetric response to carboxylates, such as acetate, have been synthesised. Alteration of the anion binding sites allows for binding site competition within a receptor. This results in a delayed colourimetric response for urea derivatives compared with pyridinium systems because the anions are initially bound to the periphery of the receptor, away from the viologen unit. DFT calculations and experimental measurements allow the colour change to be assigned to an anion-receptor charge-transfer process, facilitated by the exceptionally low reduction potential of the cationic host compounds. Evidence for electron transfer to give the viologen radical cation is also seen in some cases.

Strong ion pair charge transfer interaction of 1,8-naphthalimide–bipyridinium conjugates with basic anions – towards the development of a new type of turn-on fluorescent anion sensors

“…10 Attaching various coordination spheres to the viologen unit, colorimetric anion sensors have been constructed. [11][12][13][14][15] They indicated the binding of the anion via a new absorption band that belonged to the IPCT transition. It was found in these studies that in polar aprotic solvents, the electron transfer between viologens and some basic anions took place directlywithout photoexcitation -resulting in the formation of radicaloid species.…”

“…2, to the addition of Lewis base type anions which had been reported to form radicals directly with viologens. [11][12][13][14][15] It was hoped that upon coupling a 1,8-naphthalimide (NI) fluorophore to the bipyridinium unit, the binding of anions will be indicated by fluorescence enhancement, in addition to coloration.…”

Chromogenic and fluorogenic chemosensors and reagents for anions. A comprehensive review of the years 2010–2011

“…19 for structures) displayed colorimetric sensing properties to the carboxylate anions in CH 3 CN. 38 Anaerobic UV-Vis titrations were performed on compounds 53-56 in CH 3 CN with AcO -, succinate and malonate.…”

Selective “naked-eye” sensing of acetate ion based on conformational flexible amide-pyridinium receptor

“…L1 comprises tri-substituted benzene as the core to control the direction of the arms and pyridinium amide as the main binding motif to bind anions, which exhibited excellent binding ability toward anions recently reported by us [22] and other groups [23][24][25][26][27][28][29][30][31]. Furthermore, the nitrophenyl group was chosen since it can not only enhance the hydrogen donating property of amide NH but also act as a signaling part by charge transfer mechanism [32].…”