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 diffe rent surface-substituted thiolate-capped 30 Angstrom cadmium sulfide quantu m-confined nanoclusters was studied. HPLC analysis demonstrates that decomp osition 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 sigma(p) parameter for the remote substituent indic ates that both electron donors and accepters enhance the rate and is mimick ed by nanocluster fluorescence quenching efficiencies of the substituents, suggesting a photodecomposition mechanism involving facile electronic commu nication between the quantum dot: core and the remote substituent. Further evidence for the mechanism was obtained from the product distribution ratio s of the photodecomposition of a 4-nitrothiolate/4-methylthiolate-mixed sur face nanocluster.