Ratiometry of monomer/excimer emissions of dipyrenyl calix[4]arene in aqueous media

Variations in the ratio of monomer/excimer emissions from pyrenyl groups bound to a calix[4]arene through facing carboxamidomethyl substituents have been investigated in H2O/CH3CN mixtures. Above a level of 50% H2O, monomer emission declines and the excimer emission concomitantly increases. DFT calculations support the argument that disruption of intramolecular NHO bonds by water results in a geometry, which favors contact of the pyrene units and thus a strong excimer emission. Addition of Fe(III) to a H2O/CH3CN (4:1, v/v) solution of 1 at pH 6.1 quenches both monomer and excimer emissions through electron transfer (eT) from excited pyrene to the metal ion.