Photoinduced charge transfer between CdSe quantum dots and p-phenylenediamine

The excited state interaction between CdSe nanocrystals and a hole acceptor, p-phenylenediamine (PPD), is probed using emission and transient absorption spectroscopies. The changes in the photophysical properties of CdSe nanocrystals arising from the interaction with PPD are compared with an aliphatic amine, n-butylamine (n-BA). At low concentrations (<0.5 mM) n-butylamine enhances the emission of CdSe quantum dots whereas PPD effectively quenches the emission at similar concentrations. The low oxidation potential of PPD (Edegrees = 0.26 V vs NHE) enables it to act as an effective scavenger for photogenerated holes. A surface bound complexation equilibrium model has been proposed to explain the quenching phenomenon. The transient absorption measurements confirm the formation of PPD cation radical and subsequent formation of coupling product. Formation of such charged species at the surface extends the bleaching recovery over several microseconds.