Kinetics of ultra-fast excited state proton transfer from 7-hydroxy-4-methylflavylium chloride to water

Excited state proton transfer from 7-hydroxy-4-methylflavylium chloride to water is reported. From a modified analysis of picosecond time-resolved fluorescence data (not using the lifetime of a parent compound), all rate constants were determined: the deprotonation rate constant of the flavylium cation, k(d) = 1.4 x 10(11) s(-1), the protonation rate constant of the base form, k(p) = 2.3 x 10(10) l mol(-1) s(-1) and the reciprocal fluorescence lifetimes of these species, k(AH+) = 7.8 x 10(9) s(-1) (tau(AH+) = 128 ps) and k(A) = 7.6 x 10(9) s(-1) (tau(A) = 132 ps), in water, at 20 degrees C. The value of k(d) is the largest measured value for an intermolecular proton transfer (to water). (C) 1998 Elsevier Science B.V. All rights reserved.