Induced-Fit Anion Sensing

Abstract

Anions have many important roles in biological systems, as well as in the environment and as such there is significant interest in their binding and sensing. In induced-fit anion sensing, the binding of an anion causes a shift in the equilibrium of conformers of the molecule, which in turn may lead to a change in a physical property. In this thesis four experimental chapters describe the synthesis and anion sensing properties of a series of induced-fit anion sensors derived from a hexa-substituted triethylbenzene and diphenylacetylene motif.

Chapter one provides an introduction to anion recognition and sensing, whilst Chapter two describes a new synthetic method towards triethylbenzene receptors involving the solvent-drop grinding technique. Facile synthesis of known and novel anion receptors was achieved. Chapter three describes the use of the triethylbenzene motif, functionalised with quinolinium groups to sense anions. The receptor binds anions strongly, with complex binding observed, involving a host dimer, 2:1 host:guest and 1:1 host:guest stoichiometries. The receptor functions as a turn-off fluorescence sensor with selectivity for acetate. Chapter four describes the further functionalisation of the triethylbenzene core with the viologen moiety, leading to a series of tri- and tetrapodal anion receptors. These receptors show a colourimetic response to carboxylates through a charge transfer interaction. These receptors bind several different anions strongly. However a colourimetric response is only observed with carboxylates.

Chapter five describes the use of diphenylacetylene derivatives functionalised with urea groups which have also been investigated as induced-fit anion sensors. The receptors show a high degree of preorganisation, except for free rotation around the acetylene bond. The receptors bind a range of anions to varying extents, with strong binding observed with basic anions. Upon the addition of anions, several different fluorescent responses are observed depending on the receptor design. A turn-on fluorescent response is observed with diphenylacetylene and diphenylbutadiyne derivates due to planarisation of the receptor. Fluorescent quenching is also observed with several receptors and can allow for the discrimination of several anions when the receptors are used as part of an array. The diphenylbutadiyne derivative can also be incorporated into a dipstick which shows a turn-off response in the presence of chloride.