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-343) adsorbed on TiO 2 nanoparticles are studied by picosecond transient absorption and time-resolved fluorescence spectroscopy. The direct detection of electrons in the nanoparticles and the parent cation are monitored using picosecond 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 from the nanoparticles to the parent cation, a low quantum yield red-shifted charge transfer emission is observed. Measuring the charge transfer emission lifetimes by a picosecond time-resolved fluorimeter, we get an exact rate of back electron transfer reaction from the nanoparticle to the parent cation.