Ultrafast Electron Transfer from CdSe Quantum Dots to an [FeFe]-Hydrogenase Mimic

Abstract

The combination of CdSe nanoparticles as photosensitizers with [FeFe]-hydrogenase mimics is known to result in efficient systems for light-driven hydrogen generation with reported turnover numbers in the order of 10 4 -10 6 . Nevertheless, little is known about the details of the light-induced charge-transfer processes. Here we investigate the timescale of light-induced electron transfer kinetics for a simple model system consisting of CdSe quantum dots (QDs) of 2.0 nm diameter and a simple [FeFe]-hydrogenase mimic adsorbed to the QD surface under non-catalytic conditions. Our (time-resolved) spectroscopic investigation shows that both hot electron transfer on a sub-ps timescale and band-edge electron transfer on a sub-10-ps timescale from photoexcited QDs to adsorbed [FeFe]-hydrogenase mimics occurs. Fast recombination via back-electrontransfer is observed in the absence of a sacrificial agent or protons, which, under real catalytic conditions, would quench remaining holes or could stabilize the charge separation, respectively.

Photoinduced Fano Resonances between Quantum Confined Nanocrystals and Adsorbed Molecular Catalysts

“…The faster XB decay kinetics in CdS–FeFe can be attributed to electron transfer from the CdS NR to FeFe, driven by the ∼0.11 eV energy offset between the conduction band of CdS and the first reduction potential of FeFe (Figure a inset) . This assignment is further supported by the derivative-like TA spectra of CdS–FeFe at >1 ns (Figure b inset), which is a characteristic feature of the charge separated state caused by the shift of band-edge exciton transition energy of CdS NRs in the presence of an interfacial electric field (Stark effect). , The singly reduced FeFe – was previously reported to have a characteristic peak at ∼500 nm, but no such feature is observed here.…”

Lateral Charge Migration in 1D Semiconductor-Metal Hybrid Photocatalytic Systems

“…Our model accounts for the presence of bare rods together with the tipped rods (see Table 1) and for tipped nanorods that do not undergo charge separation. 12,37 In the region of 400-500 nm, reflecting on the bleach of CdS localized excitonic transitions, we modeled the accelerated bleach recovery of tipped rods with two time constants (τET,1 and τET,2), which reflect the electron transfer to the Ni tip. In addition, we separately modeled the CdS bleach dynamics in non-functionalized samples by four time constants (Table 2).…”

Mechanistic Insights into Selective Sensing of Pb2+ in Water by Photoluminescent CdS Quantum Dots

“…As stated previously, the PA signal arises due to trapped holes. The modulation of PA magnitude indicates disruption of the surface structure, specifically hole traps. ,, The capping agent, PEI, preferentially caps the Cd atoms with its amine functional groups, and its interaction with S atoms is rather weak. , Pb 2+ ions upon surface interaction may easily dislodge such weak surface S atom–capping ligand interactions, leading to the formation of exposed unpassivated S atoms, which are associated with hole trap states; thus consequently, the PA signal magnitude increases, indicating increased population of trapped holes. A similar mechanism has been proposed for the interaction of CdTe QDs with silver nanoparticles and Cd-chalcogenide QDs with a phenothiazine derivate as the acceptor .…”