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, kd=1.4×1011 s−1, the protonation rate constant of the base form, kp=2.3×1010 l mol−1 s−1 and the reciprocal fluorescence lifetimes of these species, kAH+=7.8×109 s−1 (τAH+=128 ps) and kA=7.6×109 s−1 (τA=132 ps), in water, at 20°C. The value of kd is the largest measured value for an intermolecular proton transfer (to water).