Charge transfer emission in coumarin 343 sensitized TiO2 nanoparticle: A direct measurement of back electron transfer

Electron injection and back electron transfer dynamics in coumarin 343 (C-3 43) adsorbed on TiO2 nanoparticles are studied by picosecond transient abso rption and time-resolved fluorescence spectroscopy. The direct detection of electrons in the nanoparticles and the parent cation are monitored using p icosecond transient absorption spectroscopy, and the corresponding dynamics of the adsorbate are monitored by time-resolved absorption spectra of the cation radical of C-343 in the visible region. When the electron returns fr om the nanoparticles to the parent cation, a low quantum yield red-shifted charge transfer emission is observed. Measuring the charge transfer emissio n lifetimes by a picosecond time-resolved fluorimeter, we get an exact rate of back electron transfer reaction from the nanoparticle to the parent cat ion.