Condensation of 2-(2'-aminophenyl)benzoxazole with
p-toluenesulfonyl chloride and phenyl isocyanateyields two new anion sensors (TABO and PUBO), which can undergo excited-state intramolecular protontransfer (ESIPT) upon excitation. For the acid receptor TABO, the ESIPT process can be readily disturbedby basic anions such as F
-, CH
3COO
-, and H
2PO
4- by deprotonating the sulfonamide unit, whereas inthe case of PUBO, a good hydrogen-bonding donor, the ESIPT process is inhibited either by the fluoride-induced deprotonation of the urea unit or by the formation of a strong CH
3COO
--urea intermolecularhydrogen bond complex, and these two types of inhibition mechanisms consequently result in differentratiometric responses. But other anions with less hydrogen-bonding acceptor abilities cannot inhibit theESIPT. Interestingly, the different inhibition abilities of F
-, CH
3COO
-, and H
2PO
4- produce differentspectral behaviors in PUBO, so this new sensor successfully distinguishes the subtle difference in thesethree anionic substrates of similar basicity and surface charge density.
