Excited-state prototropic equilibrium dynamics of 6-hydroxyquinoline encapsulated in microporous catalytic faujasite zeolites.
The excited-state proton transfer and geminate recombination of 6-hydroxyquinoline (6HQ) encaged in catalytic Na(+)-exchanged faujasite zeolites X (NaX) and Y (NaY) have been explored by measuring steady-state and picosecond time-resolved spectra. The pathways and rate constants of proton transfer of excited 6HQ are determined by the microscopic environment of zeolitic hosts surrounding the guest molecules. The excited-state proton transfer of a 6HQ molecule encapsulated in a zeolitic nanocavity is initiated by deprotonation of the enolic group to form an anionic intermediate and completed by subsequent protonation of the imino group to form a zwitterionic tautomer. Geminate recombination occurs to compete with proton transfer at each tautomerization step of excited-state 6HQ because of the confined environment of dehydrated zeolitic supercages. Consequently, excited-state equilibria among three prototropic species of 6HQ are established in microporous catalytic faujasite zeolites. Kinetic differences in NaX and NaY are attributed to dissimilarities in acidity/basicity.
Park
Sun-Young
SY
School of Chemistry, Seoul National University, NS60, Seoul 151-742, Korea.
Yu
Hyunung
H
Park
Jiho
J
Jang
Du-Jeon
DJ
D002384:Catalysis; D006863:Hydrogen-Ion Concentration; D006912:Hydroxyquinolines / Q000737:chemistry*; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D011522:Protons; D013997:Time Factors; D017641:Zeolites / Q000737:chemistry*
D006912:Hydroxyquinolines; D011522:Protons; C539489:faujasite; D017641:Zeolites; C071287:6-hydroxyquinoline