Ultrafast measurements of charge and excited-state intramolecular proton transfer in solutions of 4′-(N,N-dimethylamino) derivatives of 3-hydroxyflavone

Transient spectra for 4'-(N,N-dimethylamino)-3-hydroxy- (1a) and 4'-(N,N-dimethylamino)-3-methoxyflavone (2a) in several solvents at room temperature are reported following excitation with pulses of approximately 100 A fwhm. la exhibits emission from both the normal excited state and from the excited tautomer produced following excited-state intramolecular proton transfer (ESIPT). Rate constants for the ESIPT process are found to vary between 3.3 x 10(11) and 3 x 10(10) s(-1) depending on the solvent. Polar solvents are found to play a significant role in stabilizing the normal excited state of both 1a and 2a.