synthesis and the organic-inorganic interface.

Inorganic nanocrystals and nanoparticles have aroused increasing attention in the last few years due to their original size/shape dependent optoelectronic, thermodynamic, mechanical and catalytic properties. The ability to strongly exploit the original potential of such nano-objects and access their properties relies on the ability of finely tune their size, shape, crystalline phase, and surface chemistry. In this regard, soft chemistry routes provide suitable tools to a priori design and synthetize nano-object with tailored physical-chemical properties as function of the final purpose. Furthermore, conveying the peculiar properties of inorganic nanocrystals to the mesoscopic scale and integrating them in macroscopic entities is the key point to properly exploit their unprecedented functionality for biomedical, optoelectronic, catalytic, energy conversion applications.

Colloidal nanocrystal synthesis and the organic-inorganic interface

Colloidal Nanocrystal Synthesis and the Organic-Inorganic ..

“Colloidal Nanocrystal Synthesis and the Organic-Inorganic Interface

After synthesis, the organic pigmentmicronanocrystals were isolated by adding cyclohexane in a volumeratio of 3:1 to the crude colloidal solutions, followed by centrifugation(relative centrifugal force = 14.100 g, 5 min) and redispersion inchloroform. The washing step was repeated four times before the micronanocrystalswere stored in chloroform or in chlorobenzene.

Colloidal nanocrystal synthesis and the organic–inorganic interface.

This paper provides an overview of the
synthetic techniques used to prepare colloidal
nanocrystals (NC) of controlled composition,
size, shape, and internal structure and the
methods for manipulation of these materials
into ordered NC assemblies (superlattices).
High-temperature solution-phase synthesis
(100–300°C) is followed by size-selective
separation techniques in the preparation of
monodisperse NC samples tunable in size
from1 to 15 nm in diameter with5%
standard deviation. Each NC consists of a
crystalline inorganic core coordinated by an
organic monolayer. These monodisperse
NC samples enable systematic studies of
structural, electronic, magnetic, and optical
properties of materials as a function of size
evolution from molecular species (100 atoms)
to bulk solids (1 atoms). We illustrate
size-dependent properties for magnetic
materials using Co and for semconducting
materials using PbSe. These NC samples are
sufficiently uniform in size to self-assemble
into close-packed, ordered NC superlattices,
also known as colloidal crystals.

Journal of Nanoscience and Nanotechnology

An important consideration foreventual practical use of thesematerials, e.g., for applications at the interface to biochemistryor in epidermal electronics,, is the stability ofthe organic nanocrystals in aqueous environments. Stability was testedfor epindolidione nanocrystal films deposited on glass substrates,which were completely immersed in aqueous solutions with an acidicpH value, as an extreme model substance mimicking human sweat. In Figure c, a 12% decreaseof the PL intensity within 120 min is shown. In comparison, a filmof standard inorganic nanocrystals emitting at the same wavelengthas epindolidione, namely CdSe/ZnS core/shell nanocrystals, exhibitsa 6-fold larger drop of PL intensity within the same time span. Thus,the high optical quality of the fabricated organic pigment nanocrystalstogether with their superior stability holds strong promise for theirexploitation in future photonic applications as a replacement to inorganicnanocrystals, which usually contain toxic heavy metals.

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The pigments were solubilized by attachment of t-Boc protection groups The t-butoxycarbonylation is performed by stirring the pigments in anorganic solvent (for details see the section) at room temperature together with di(t-butyl)-dicarbamate, using N,N′-dimethylaminopyridineas catalyst. An exception here is phthalocyanine, which is first lithiatedto provide sufficient reactivity to di(t-butyl)-dicarbamate,replacing the necessity to apply any catalyst. The replacement ofthe H atoms of the NH groups by t-Boc removes thepossibility of intermolecular H-bonding, which inhibits crystallizationof the molecules to pigments, and thus eliminates any intermolecularcoupling of electronic states. As a consequence, the absorption spectraof the latent pigments are hypsochromically shifted in respect tothat of the initial parent pigments (). Such a behavior has been reported before for instance for t-Boc protected quinizarin andquinacridone, and we observed it forall 5 pigments shown in Figure , where thelatent pigment of quinacridone appears yellow, due to an absorptiononset at 525 nm, whereas the pigment used as starting material exhibitcolors from red to violet. With the exceptionof bis-t-Boc-indigo, all latent pigments exhibitalso intense PL (Figure ). Under illuminationwith an UV lamp the luminescence is observed by the bare eye in colorsranging between red, for t-Boc-phthalocyanine, andblue, observed for bis-t-Boc-epindolidione (Figure c). The absence of intense PL in the case of bis-t-Boc-indigo is not surprising, because for indigo a radiationlessinternal conversion process has been described to dominate over theradiative recombination, independent of the attachment of substitutions. Most important is, however, that protectingthe insoluble parent pigments by t-Boc groups improvestheir solubility in organic solvents by approximately 5 orders ofmagnitude. This high solubility makesthe latent pigments ideal precursors for the following syntheses ofcolloidal micro- and nanocrystals.

Surface modification, functionalization and …

We invite contributors to submit original papers that account for recent advances in the field of inorganic nanocrystal and nanoparticles synthesis and characterization, their surface engineering and functionalization, and their applications.