Simultaneous positive and negative optical patterning with dye-sensitized CdSe quantum dots.

CdSe quantum dots are functionalized with the organic dye iron ß-tetraaminophthalocyanine to reward a solution-processable hybrid material with two individually addressable optical resonances. We exploit this dual functionality during optical write/optical read patterning experiments and show that it is possible to simultaneously write complex optical patterns with positive and negative fluorescence contrast. This is enabled by a fluorescence enhancement under near-resonant excitation of the quantum dots in combination with a fluorescence bleaching during excitation of the singlet transition of the phthalocyanine. The presence of the organic dye not only enables negative optical patterning but also enhances the contrast during positive patterning. Furthermore, the patterning result is strongly dependent on the excitation wavelength during readout. Our results highlight the new possibilities that arise from combining inorganic quantum dots and organic π-systems into hybrid nanocomposites.

Opportunities and challenges for electrochemistry in studying the electronic structure of nanocrystals.

We review the state-of-the-art of determining the electronic structure of nanocrystals in thin films by electrochemistry. Our core conclusion, the necessity of combining electrochemical with spectroscopic techniques, is illustrated with the holistic analysis of thin films of CdSe nanocrystals cross-linked with electroactive metal ß-tetraaminophthalocyanines by differential pulse voltammetry, optical spectroscopy and potential modulated absorption spectroscopy. We show that the same nanocrystals cross-linked with phthalocyanines of different metal centers exhibit rather similar electrochemical signatures, but behave distinctly different in spectroelectrochemical investigations. We argue that in one case, namely CdSe nanocrystals cross-linked with Co ß-tetraaminophthalocyanine, we find supporting evidence for the hybridization of energy levels at the organic/inorganic interface. This work suggests that spectroelectrochemistry is capable of revealing the electronic structure of complex nanomaterials, such as semiconductor nanocrystals functionalized with organic pi-systems.