Pyrene-appended α-Cyclodextrin as a Fluorescent pH Probe Responding to a Wide Range

Pyrene-appended α-cyclodextrin (3) in which a trimethylenediamine linker connected the pyrene residue to the α-cyclodextrin moiety showed pH-dependent fluorescence intensity changes. The fluorescence intensity was almost linearly changed within the pH range of 5 - 10. The unique fluorescence response of 3 to the pH was due not only to the favorable pKa values (pKa1 = 6.4 and pKa2 = 8.8), but also to the almost equal contributions of the amino groups to the pyrene's fluorescence quenching.