We carried out fluorescence titration experiments of the receptor (L) [10 l M] with the AcO ? (200 l M) in acetonitrile. The fluorescence response of the receptor L with AcO ? was recorded with an
excitation at 373 nm. As shown in Figure 6, there is no significant
change observed in the emission spectrum of the receptor after the
addition of excess amount of acetate salt. However, the minor increase of fluorescence intensity suggests that the ICT process operates due to the occurrence of a tautomeric equilibrium during the
anion recognition process (Scheme 2)