26 research outputs found
Supramolecular assemblies of semiconductor quantum dots and a bis(bipyridinium) derivative : luminescence quenching and aggregation phenomena
We have synthesized CdSe and CdSe–ZnS core–shell luminescent nanocrystal quantum dots and studied
their interaction with a ditopic bis(bipyridinium) compound in solution. The latter strongly quenches the
luminescence of the quantum dots by a static mechanism, indicating that the nanocrystal and molecular
components undergo association in the ground state. Photoexcitation of these inorganic–organic
hybrids causes an electron-transfer process from the conduction band of the nanocrystal to the LUMO
of the molecule. The ability of the bipyridinium-type species to trigger association of the quantum dots
is evidenced by spectrofluorimetric titrations and DLS measurements in solution, and confirmed by TEM
experiments on surfaces. The quantum dot–molecule complexes can be disassembled in solution by
addition of a calixarene host capable of encapsulating the bipyridinium units of the molecular connector.
Our results demonstrate that supramolecular chemistry offers convenient ways to control the
aggregation of semiconductor nanocrystals, a crucial task for the generation of nanostructured arrays
with well defined properties
Supramolecular assemblies of semiconductor quantum dots and a bis(bipyridinium) derivative: luminescence quenching and aggregation phenomena
We have synthesized CdSe and CdSe\u2013ZnS core\u2013shell luminescent nanocrystal quantum dots and studied
their interaction with a ditopic bis(bipyridinium) compound in solution. The latter strongly quenches the
luminescence of the quantum dots by a static mechanism, indicating that the nanocrystal and molecular
components undergo association in the ground state. Photoexcitation of these inorganic\u2013organic
hybrids causes an electron-transfer process from the conduction band of the nanocrystal to the LUMO
of the molecule. The ability of the bipyridinium-type species to trigger association of the quantum dots
is evidenced by spectrofluorimetric titrations and DLS measurements in solution, and confirmed by TEM
experiments on surfaces. The quantum dot\u2013molecule complexes can be disassembled in solution by
addition of a calixarene host capable of encapsulating the bipyridinium units of the molecular connector.
Our results demonstrate that supramolecular chemistry offers convenient ways to control the
aggregation of semiconductor nanocrystals, a crucial task for the generation of nanostructured arrays
with well defined properties
An Efficient Method for the Surface Functionalization of Luminescent Quantum Dots with Lipoic Acid Based Ligands
We describe herein an operationally advantageous general methodology for efficiently activating lipoic acid based compounds, a family of popular surface ligands for semiconductor nanocrystals, through the use of a borohydride exchange resin, and the use of the activated species to replace the native surface ligands of quantum dots. The procedure enabled phase transfer of the nanocrystals between polar and aqueous media and, if unsubstituted lipoic acid was used, a facile adjustment of their solubility in a wide range of solvents with varying polarity (from hexane to water). We show that the protocol is applicable to different types of nanocrystals and a variety of lipoic acid based ligands, and that the resulting quantum dots maintain their optical properties, in particular, an intense luminescence, and long-term colloidal stability
An efficient method for the surface functionalization of luminescent quantum dots with lipoic acid-based ligands
We describe an operationally advantageous general methodology to efficiently activate lipoic acid-based compounds - a
family of popular surface ligands for semiconductor nanocrystals - by
the use of a borohydride exchange resin, and the use of the activated species to replace the native surface ligands of quantum dots. The procedure enables the phase transfer of the nanocrystals between
polar and aqueous media and, if unsubstituted lipoic acid is used, a
facile adjustment of their solubility in a wide range of solvents with varying polarity (from hexane to water). We show that the protocol is applicable to different types of nanocrystals and a variety of lipoic acid-based ligands, and that the resulting quantum dots maintain their optical properties - in particular, an intense luminescence - and long
term colloidal stability
Synthesis and properties of ZnTe and ZnTe/ZnS core/shell semiconductor nanocrystals
Nanocrystals obtained by growing a protecting ZnS shell onto a photoactive ZnTe core afford nanocrystals that can represent alternatives to cadmium-based quantum dots
Synthesis and photophysical investigation of novel supramolecular lanthanide luminescent architectures
THESIS 9172This thesis is entitled "Synthesis and photophysical investigations of novel supramolecular
architectures" and is composed of five chapters. In the first chapter the photopysical and
chemical properties of the lanthanide ions was described and this was followed by a
discussion on the potential different methods in order to build highy geometric lanthanide
complexes, using various approaches such as the use of macrocyclic ligands, podand and
lanthanide directed formation of self-assemblies, which as been most particularly
described
Electrochemical properties of CdSe and CdTe quantum dots
none4noSemiconductor nanocrystal quantum dots (QDs), owing to their unique opto-electronic properties determined by quantum confinement effects, have been the subject of extensive investigations in different areas of science and technology in the past two decades. The electrochemical behaviour of QDs, particularly for CdSe and CdTe nanocrystals, has also been explored, although to a lesser extent compared to the optical properties. Voltammetric measurements can be used to probe the redox levels available for the nanocrystals, which is an invaluable piece of information if these systems are involved in electron transfer processes. Electrochemical data can also foster the interpretation of the spectroscopic properties of QDs, and give insightful information on their chemical composition, dimension, and surface properties. Hence, electrochemical methods constitute in principle an effective tool to probe the quality of QD samples in terms of purity, size dispersion, and surface defects. The scope of this critical review is to discuss the results of electrochemical studies carried out on CdSe and CdTe core and core-shell semiconductor nanocrystals of spherical shape. Examples of emerging or potential applications that exploit electroactive quantum dot-based systems will also be illustrated.mixedM. Amelia; C. Lincheneau; S. Silvi; A. CrediM. Amelia; C. Lincheneau; S. Silvi; A. Cred
Hybrids of semiconductor quantum dot and molecular species for photoinduced functions
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
Synthesis of Semiconductor Nanocrystals, Focusing on Nontoxic and Earth-Abundant Materials
International audienceWe review the synthesis of semiconductor nanocrystals/colloidal quantum dots in organic solvents with special emphasis on earth-abundant and toxic heavy metal free compounds. Following the Introduction, section 2 defines the terms related to the toxicity of nanocrystals and gives a comprehensive overview on toxicity studies concerning all types of quantum dots. Section 3 aims at providing the reader with the basic concepts of nanocrystal synthesis. It starts with the concepts currently used to describe the nucleation and growth of monodisperse particles and next takes a closer look at the chemistry of the inorganic core and its interactions with surface ligands. Section 4 reviews in more detail the synthesis of different families of semiconductor nanocrystals, namely elemental group IV compounds (carbon nanodots, Si, Ge), III–V compounds (e.g., InP, InAs), and binary and multinary metal chalcogenides. Finally, the authors’ view on the perspectives in this field is given
Chemistry of InP Nanocrystal Syntheses
International audienc