Probing Wave Functions at Semiconductor Quantum-Dot Surfaces by Non-FRET Photoluminescence Quenching

Steady-state photoluminescence (PL) quenching of colloidal CdSe/ZnS and CdSe quantum dots (QDs) induced by functionalized porphyrin molecules was investigated for various QD sizes. The majority of the observed strong quenching of the QD photoluminescence can be assigned to neither Forster resonant energy transfer (FRET) nor photoinduced charge transfer between the QDs and the chromophore. Using the remaining small FRET efficiency to monitor the formation of QD/chromophore nanoassemblies, the major contribution to PL quenching was found to be proportional to the calculated quantum-confined exciton wave function at the QD surface. The quenching depends on the QD size and shell and is stronger for smaller quantum dots. Upon comparison of experimentally determined quenching rates and calculations of the exciton wave function, it was concluded that the attachment of only one chromophore induces a pertubation of the wave function that is accompanied by a strong increase of the radiationless decay rate.