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Amelia M.,University of Bologna | Font M.,University of Bologna | Credi A.,University of Bologna | Credi A.,Interuniversity Center for the Chemical Conversion of Solar Energy
Dalton Transactions | Year: 2011

We have investigated chloroform solutions containing tris(4,7-diphenyl-1, 10-phenanthroline) ruthenium(ii) and CdTe nanocrystal quantum dots (5.6 nm diameter). The electronic levels of these two components are such that the Ru complex can act as an energy donor towards the quantum dot, which can thus behave as an energy acceptor. Steady-state and time-resolved spectroscopic experiments indicate that the Ru complexes and the CdTe nanocrystals self-assemble to give stable 1:1 adducts, in which the luminescence of the former units is strongly quenched. Such a quenching can be ascribed to either energy transfer to the CdTe quantum dot, or to electron transfer from the CdTe valence band to the excited Ru complex. However, no supporting evidence for the occurrence of photoinduced energy transfer in the adduct could be found. The CdTe luminescence is also slightly quenched in the presence of the ruthenium complex. The strong association of the metal complexes with the nanocrystals suggests that self-assembly strategies may be effectively employed to achieve surface functionalization of semiconductor quantum dots with molecular units. © 2011 The Royal Society of Chemistry. Source

Oszajca M.,University of Bologna | Oszajca M.,Jagiellonian University | Lincheneau C.,University of Bologna | Amelia M.,University of Bologna | And 6 more authors.
European Journal of Inorganic Chemistry | Year: 2013

We have investigated the spectroscopic properties of CdSe and CdSe-ZnS nanocrystal quantum dots (QDs) in the presence of the electron acceptor tetracyanoethene (TCNE) in organic solution. Our results indicate that TCNE reacts with the n-alkylamine capping ligands at the surfaces of nanocrystals to generate (cyanovinyl)amine products that remain bound to the surfaces of the QDs, substantially increasing their emission efficiency. Further addition of an excess of TCNE caused a decrease in the luminescence intensity, most likely because of an electron-transfer quenching process from the photoexcited nanocrystals to the electron-accepting TCNE molecules. TCNE-induced emission enhancement was also observed for the strongly luminescent CdSe-ZnS core-shell QDs. This approach enables a post-synthetic adjustment of the luminescence efficiency of amine-capped QDs. We have also shown that the threshold-dependent response of the QD emission on the TCNE concentration can be used to encode NAND and XOR Boolean logic operations. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Lincheneau C.,University of Bologna | Amelia M.,University of Bologna | Oszajca M.,University of Bologna | Oszajca M.,Jagiellonian University | And 14 more authors.
Journal of Materials Chemistry C | Year: 2014

We report the synthesis of spherical ZnTe nanocrystals and the successive coating with a ZnS shell to afford core/shell quantum dots. These nanocrystals can represent alternatives to cadmium-based quantum dots but their preparation and properties are challenging and relatively unexplored. The effect of various synthetic parameters on the reaction outcome was investigated, and the resulting nanocrystals were characterized by TEM, EDX, XPS, and spectroscopic measurements. The optical data indicate that these core/shell quantum dots belong to type I, i.e., both the electron and the hole are confined within the ZnTe core. Both the ZnTe core and ZnTe/ZnS core/shell quantum dot samples absorb in the visible region and are not luminescent. The ZnS shell preserves the optical properties of the core and improves the chemical and photochemical stability of the nanoparticles in air equilibrated solution, whereas they appear to be quite fragile in the solid state. XPS results have evidenced the distinct nature of core and core/shell QDs, confirming the formation of QDs with shells of different thicknesses and their evolution due to oxidation upon air exposure. Anodic photocurrent generation was observed when an ITO electrode functionalized with ZnTe/ZnS nanocrystals was irradiated in the visible region in a photoelectrochemical cell, indicating that the quantum dots perform spectral sensitization of the electron injection into the ITO electrode. Conversely, cathodic photocurrent generation was not observed; hence, the QD-modified electrode performs electrical rectification under a photon energy input. © 2014 the Partner Organisations. Source

Avellini T.,University of Bologna | Lincheneau C.,University of Bologna | Vera F.,University of Bologna | Silvi S.,University of Bologna | And 3 more authors.
Coordination Chemistry Reviews | Year: 2014

Semiconductor quantum dots are inorganic nanocrystals which, because of their unique size-dependent electronic properties, are of high potential interest for the development of light-responsive nanodevices. Their surface can be chemically modified, by either covalent or non-covalent approaches, in order to interface them with molecular units endowed with specific physico-chemical properties. Photoinduced electron- and energy-transfer processes between quantum dots and attached molecular species offer versatile strategies to implement functionalities such as photosensitized processes, and luminescence sensing and switching. In this review we will discuss the strategies underlying the rational construction of this kind of multicomponent species, and we will illustrate a few examples taken from our own research. © 2013 Elsevier B.V. Source

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