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Excited‐State Prototropic Equilibrium Dynamics of 6‐Hydroxyquinoline Encapsulated in Microporous Catalytic Faujasite Zeolites
Author(s) -
Park SunYoung,
Yu Hyunung,
Park Jiho,
Jang DuJeon
Publication year - 2010
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201000734
Subject(s) - faujasite , chemistry , tautomer , excited state , protonation , deprotonation , photochemistry , proton , molecule , catalysis , zeolite , organic chemistry , atomic physics , ion , physics , quantum mechanics
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.