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Title: Dramatic Pressure-Dependent Quenching Effects in Supercritical CO2 Assessed by the Fluorescence of 4‘-Dimethylamino-3-hydroxyflavone. Thermodynamic versus Kinetics Control of Excited-State Intramolecular Proton Transfer
Authors: Barroso, Mónica 
Chattopadhyay, Nitin 
Klymchenko, Andrey S. 
Demchenko, Alexander P. 
Arnaut, Luís G. 
Formosinho, Sebastião J. 
Issue Date: 21-Dec-2006
Publisher: American Chemical Society
Citation: The Journal of Physical Chemistry A. 110:50 (2006) 13419-13424
Abstract: Steady-state fluorescence of 4‘-dimethylamino-3-hydroxyflavone (DMA3HF) was observed in supercritical carbon dioxide (scCO2). Excited-state intramolecular proton transfer (ESIPT) occurs resulting in two well-separated emission bands corresponding to the normal and tautomer forms. As the scCO2 density exceeds 0.7 g/mL, the relative intensity of the two bands tends to a constant value, comparable to that observed for organic solvents with ET(30) = 33.0 ± 0.5 kcal/mol, such as toluene and di-n-butyl ether. At lower densities, the substantial decrease of the total fluorescence intensity (a 600-fold decrease as the pressure decreases from 100 to 80 bar) is accompanied by an even more accentuated decrease of the tautomer fluorescence. This can be explained by a shift in the equilibrium between normal and tautomer forms, concomitant with a more efficient quenching of the less solvated fluorophore, that may change the thermodynamic control of the relative population of the two emissive species to a kinetic control.
ISSN: 1089-5639
DOI: 10.1021/jp0643606
Rights: openAccess
Appears in Collections:FCTUC Química - Artigos em Revistas Internacionais

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