PROTROPIC AND PHOTOPHYSICAL PROPERTIES OF 7-HYDROXYQUINOLINE IN X AND Y ZEOLITES

Diffuse reflectance and emission spectra of 7-hydroxyquinoline intercalated in the supercage of X and Y zeolites are compared with the absorption and emission spectra of aqueous 7-hydroxyquinoline solutions at various pH to understand protropic and photophysical properties of 7-hydroxyquinoline in zeolite microenvironments. Predominance of zwitterionic spedes with significant existences of the other three protropic equilibrium species, normal, protonated and deprotonated species in zeolite samples indicates that the major fraction of the molecules interact with strong acid and base sites of zeolite at an adsorbed position. Observed zeolite pHs of near neutrality are established by a near balance in numbers of many strong acid and base sites rather than by'small numbers or weakness of acid and base sites. Excitations of nonzwitterionic species such as deprotonated species also give prevailing zwitterionic fluorescence, indicating that excited and ground proton transfer cycles of protropic species can be triggered by photons in organized zeolite media as well as in water.