http://nova.newcastle.edu.au/vital/access/services/Feed ${session.getAttribute("locale")} 5 http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:9548 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. 2011-11-30T05:00:05.323Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:4763 Two new viologen-based anion hosts, 2 and 3, are reported, incorporating two tripodal binding domains. Binding of carboxylate anions, particularly acetate, malonate and succinate by pyridinium derivative 2 results in an intense purple colouration. DFT calculations on representative system 2·malonate reveal that this absorption arises from charge-transfer from the anion to the bipyridinium unit. Anion binding by 3 does not initially result in a colour change because anions are bound at the periphery of the receptor; however, addition of more that two equivalents of acetate or more than one equivalent of dicarboxylate turn the colourimetric response on. 2010-04-27T05:32:55.248Z ]]>