Competition of branch-to-core exciton localization and interfacial electron transfer in CdSe tetrapods

Abstract

Quantum confined nanorod heterostructures offer the opportunity to control the energy of electrons and holes by rod diameters and the spatial location of carriers along the long axis through their length. We showed that CdSe tetrapods had a quasi-type II band alignment between the Zinc Blend CdSe quantum dot core and four Wurtzite CdSe nanorod branches and 88% of the excitons generated in the CdSe branches localized to the core with a time constant of 1.01±0.06ps, driven by the lower conduction band energy in the core. We demonstrated that electron transfer to methylene blue molecules (with an average time constant of 33±8ps) occurred after the exciton were localized to the core, while ultrafast electron transfer (0.31±0.01ps) to methyl viologen occurred prior to the localization of the exciton. Thus, the competition of exciton interfacial dissociation and transport along the rod enabled the control of the nature of charge separated states in nanorod-electron acceptor complexes.