Park Han Jung, Kwon Oh-Hoon, Ah Chil Seong, Jang Du-Jeon
School of Chemistry, Seoul National University, NS60, Seoul 151-742, Korea.
J Phys Chem B. 2005 Mar 10;109(9):3938-43. doi: 10.1021/jp046817m.
The excited-state tautomerization dynamics of 7-hydroxyquinoline encapsulated in beta-cyclodextrin is compared with that in pure water by measuring isotope-dependent fluorescence kinetics as well as absorption and emission spectra. The normal species tautomerizes stepwise via forming anionic intermediate species in both systems. However, the enol-deprotonation time (40 ps in water) becomes as large as 170 ps whereas the imine-protonation time of the anionic intermediate (160 ps in water) becomes as short as 85 ps in beta-cyclodextrin. The slow formation and the fast decay of the anionic species are attributed to the unstability of the charged species in hydrophobic cages. Encapsulation can be utilized to enhance fluorescence enormously and to accelerate selective reactions by retarding other processes.
