Spectroscopic investigation of the three prototropic forms of a β-cyclodextrin-indolizine derivative from its inclusion-cum-charge-transfer complexes

► A new fluorescent β-CD derivative, (1), forms inclusion-cum-CT complex with a series of quinones. ► The (pKa) values of the functional moieties of (1) can be determined from absorption, emission and CT spectra. ► The study shows that (1) is a potential fluorescent pH sensor with switching action.