Substituent dependent fluorescence response of diazacrown-based PET sensors

The sensing ability of three 1,10-diaza-18-crown-6 based sensors bearing a coumarin fluorophore was studied and compared with the analogous monoaza-18-crown-6 sensor. Coordination experiments between hosts and organic ammonium salts with varying steric demand were studied using fluorescence and 1H NMR spectroscopy. We have found that the fluorescent signal generated on complexation was greatly influenced by the structure of the sensor. Surprisingly, in two cases, we observed the decrease of fluorescence on complexation, which was attributed to changes in the conformational dynamics of the sensors on complexation.