Photoinduced Charge Separation and Recombination Processes in CdSe Quantum Dot and Graphene Oxide Composites with Methylene Blue as Linker

The charge separation and recombination processes between CdSe quantum dot (QD) and graphene oxide (GO) composites with linking molecule methylene blue (MB+) were studied by femtosecond transient absorption spectroscopy. Anchoring MB+ molecules on GO results in significant changes in steady-state and transient absorption spectra, where the exciton dissociation time in the CdSe QD-MB+-GO composite was determined to be 1.8 ps. Surprisingly, the ground state bleaching signal increased for MB+-GO complex was found to be 5.2 ps, in relation with electron transfer from QD to GO. On the other hand, the strong electronic coupling between MB center dot-GO radical and GO prolonged charge recombination process (>= 5 ns) in QD-MB+-GO composites. Charge separation and recombination processes at the interface between semiconductor QDs and graphene can thus be modulated by the functionalized dye molecules.