Excited-state proton transfer and geminate recombination in the molecular cage of beta-cyclodextrin

Abstract

Excited-state proton transfer and geminate recombination in aqueous heptakis(2,6-di-O-methyl)-β-cyclodextrin have been compared with those in water by monitoring the photoinduced prototropic tautomerization of 6-hydroxyquinoline, which occurs via forming anionic intermediate. Enol deprotonation decelerates by 18 times whereas its reverse process accelerates slightly with encapsulation. The imine protonation of the intermediate slows down by 8.2 times in the molecular cage. These unusual kinetic features have been explained with the geminate recombination of protons as well as the structural dynamics of solvent molecules and the relative energetics of involved species.