The formation of nanoassemblies of CdSe/ZnS quantum dots (QD) and pyridyl-substituted free-base porphyrin (H(2)P) molecules has been spectroscopically identified by static and time-resolved techniques. The formation of nanoassemblies has been engineered by controlling the type and geometry of the H(2)P molecules. Pyridyl functionalization gives rise to a strong complex formation accompanied by QD photoluminescence (PL) quenching. For some of the systems, this quenching is partly related to fluorescence resonance energy transfer (FRET) from the QD to H(2)P and can be explained according to the Förster model. The quantitative interpretation of PL quenching due to complexation reveals that (i) on average only about (1)/(5) of the H(2)P molecules at a given H(2)P/QD molar ratio are assembled on the QD and (ii) only a limited number of "vacancies" accessible for H(2)P attachment exist on the QD surface.

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 Fo ¨rster 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.

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