Surface Functionalization of Cadmium Sulfide Quantum-Confined Nanoclusters. 5. Evidence of Facile Surface-Core Electronic Communication in the Photodecomposition Mechanism of Functionalized Quantum Dots

The photoinduced decomposition of dimethylformamide suspensions of 10 different surface-substituted thiolate-capped 30 Å cadmium sulfide quantum-confined nanoclusters was studied. HPLC analysis demonstrates that decomposition proceeds at a constant rate and produces only precipitated cluster aggregates and the symmetric disulfide corresponding to the thiolate cap as the only organic product. The dependence of the disulfide photogeneration kinetics on the Hammett σ<INF>p</INF> parameter for the remote substituent indicates that both electron donors and acceptors enhance the rate and is mimicked by nanocluster fluorescence quenching efficiencies of the substituents, suggesting a photodecomposition mechanism involving facile electronic communication between the quantum dot core and the remote substituent. Further evidence for the mechanism was obtained from the product distribution ratios of the photodecomposition of a 4-nitrothiolate/4-methylthiolate-mixed surface nanocluster.