Ultrafast and Hot Electron Transfer in CdSe QD-Au Hybrid Nanostructures

Recently, much attention has been paid to semiconductor-metal hybrid nanostructures (HNs) in terms of efficient electron transfer from the semiconductor to the metal and semiconductor-metal HNs are one of the best candidate materials for photovoltaics and photocatalysis. However, the analyses of electron-transfer processes in semiconductor-metal HNs have focused on the electron transfer from the band-edge state in metal-attached semiconductor nanorods. Here, we synthesized and characterized CdSe quantum dots (QDs) attached with different-sized Au nanoparticles (NPs) and examined electron transfer from band-edge (1S(e)) and higher excited states using femtosecond pump-probe spectroscopy with state-selective excitation. We analyzed growth kinetics, decay dynamics, and initial bleach amplitude of the IS bleach band and found the existence of hot electron transfer from the 1P(e) state and ultrafast electron transfer with the lifetime much shorter than the instrumental response function (<< 60 fs) from the 1S(e) state of CdSe QDs to Au NPs. The lower IS bleach yields of CdSe QD-Au HNs excited at 400 nm and 1P states as compared with those of CdSe QDs can be explained in terms of hot electron transfer from the 1P(e) state and ultrafast electron transfer from the 1S(e) state.