Ultrafast Charge Separation in Multiexcited CdSe Quantum Dots Mediated by Adsorbed Electron Acceptors

Ultrafast ET with a characteristic time constant of -70 fs between CdSe QDs (mean radii of 1.4 nm) photoexcited in the lowest 1S electron state (lambda(exc) = 539 nm), and the molecular electron acceptor MV2+ adsorbed on the QD surface was observed. The photophysics of such a system was investigated by time-resolved transient absorbance spectroscopy in the UV-visible spectral region. Our studies for the coupled system as a function of excitation intensity at lambda(exc) = 387 nm show that the ET processes compete efficiently with Auger recombination in CdSe QDs and at (east 4 e-h pairs can be separated by ET to the electron acceptor MV2+.