The design of luminescent sensors for anions and ionisable analytes

A molecular luminescent sensor for anions can be built through a modular approach, i.e. by covalently linking an appropriate photoactive fragment to the receptor displaying a satisfactory affinity towards the desired substrate. Following the receptor-anion interaction, an intercomponent process must take place, e.g. an electron transfer (eT) or an energy transfer (ET) process, that distinctly modifies the emission of the luminophore, thus signalling the occurrence of the recognition event. In this article, specific molecular sensors are classified according to the type of receptor-anion interaction, whether hydrogen bonding or metal-ligand interactions, Receptors of the latter class are based on a Zn-II polyamine platform, which leaves at least a vacant coordination site for the incoming anion. Substrates include natural amino acids, NH3+-CH(R)-COO-, for which the highest selectivity is observed when the receptor subunit specifically interacts with the R portion. An eT process involving R and the nearby excited luminophore may provide the signal transduction mechanism.