Time-domain spectroscopies with time resolution shorter than the vibrational periods of interest were employed to reveal the reaction kinetics and molecular dynamics of the intramolecular charge transfer (ICT) reaction of thioflavin T in liquids. Time-resolved fluorescence spectra provided detailed reaction kinetics, and vibrational wave packets observed in the time-resolved fluorescence and transient absorption provided structural information on the reaction intermediate. Upon photoexcitation, the Franck Condon state undergoes vibrational, relaxation and minor conformational change to form a stable planar intermediate followed by the twisting of the central C C single bond to form the twisted ICT state. The ICT reaction rate is determined by the solvent fluctuation excluding the inertial component in the solvation function.