Hybrids of semiconductor quantum dot and molecular species for photoinduced functions

Semiconductor Quantum Dots as Components of Photoactive Supramolecular Architectures

Luminescent quantum dots (QDs) are colloidal semiconductor nanocrystals consisting of an inorganic core covered by a molecular layer of organic surfactants. Although QDs have been known for more than thirty years, they are still attracting the interest of researchers because of their unique size-tunable optical and electrical properties arising from quantum confinement. Moreover, the controlled decoration of the QD surface with suitable molecular species enables the rational design of inorganic-organic multicomponent architectures that can show a vast array of functionalities. This minireview highlights the recent progress in the use of surface-modified QDs - in particular, those based on cadmium chalcogenides - as supramolecular platforms for light-related applications such as optical sensing, triplet photosensitization, photocatalysis and phototherapy.

Ice Squeezing Induced Multicolor Fluorescence Emissions from Polyacrylamide Cryogels

Being short of conventional chromophores, polyacrylamide is generally not regarded as a fluorescent material. Exactly the polymerization of dilute solutions of acrylamide and N,N'-methylenebisacrylamide led to thick liquids at 60 °C, showing no fluorescence. Things changed when the phase transition of water was involved. The squeezing effect of ice crystals not only created polymeric solids (cryogels) at - 20 °C, but also endowed them unexpected fluorescence emissions. The macroporous cryogels are mainly blue fluorescent polymers. However yellow and red fluorescence were also achieved by changing the ingredient ratios. A series of instrumental detections revealed that the multicolor fluorescence were based on exquisite amido stacking induced from ice squeezing. If people make good use of the squeezing effect of the heaven-sent molecule to manipulate the interactions of monomer functionalities, cryogenic polymerization can be a promising method to produce diverse polymeric materials.

Spectral and photochemical properties of hybrid organic-inorganic nanosystems based on CdS quantum dots and merocyanine ligands

The spectral and photochemical properties of hybrid organic-inorganic nanosystems (HNSs) were investigated. HNS consisted of CdS quantum dots (QDs) functionalized with ligands containing the isothiouronium anchor group linked by a polymethylene chain with photochromic merocyanine (MC). The HNS synthesis was carried out via a microwave-assisted one-pot technique. Energy transfer from the QDs to MC in the HNS was observed and resulted in QD fluorescence quenching and MC sensitization. Compared to the free MC, trans-cis photoisomerization of MC in the HNS was suppressed and its photodestruction was accelerated. In addition, upon HNS photolysis by visible light with energy higher than the threshold, the photosensitized destruction of the QDs (which did not absorb the applied light) occurred. The observed effects were proposed to be caused by MC adsorption on QDs surface, which leads to the restriction of the MC photoisomerization and population of the surface electron trap states of the QDs.

Improving photocatalytic oxygenation mediated by polymer supported photosensitizers using semiconductor quantum dots as ‘light antennas’

Semiconductor nanoparticles (quantum dots) sensitize the photochemical generation of singlet oxygen at the surface of a photoactive polymer.

Microwave-assisted one-pot synthesis of hybrid nanosystems based on CdS quantum dots functionalized with organic chromophores: effect of the chromophore nature on the nanosystem composition

Quantum dot/organic dye nanosystems were synthesised via a one-pot technique. Different dependences of the nanosystem composition on the synthetic conditions for different dyes were observed.

Interfacing Luminescent Quantum Dots with Functional Molecules for Optical Sensing Applications

Semiconductor quantum dots possess unique size-dependent electronic properties and are of high potential interest for the construction of functional nanodevices. Photoinduced electron- and energy-transfer processes between quantum dots and surface-bound molecular species open up attractive routes to implement chemical switching of luminescence, which is at the basis of luminescence sensing. In this article, we discuss the general principles underlying the rational design of this kind of multicomponent species. Successively, we illustrate a few prominent examples, taken from the recent literature, of luminescent chemosensors constructed by attaching molecular species to the surface of quantum dots.

Energy and charge transfer in nanoscale hybrid materials

Hybrid materials composed of colloidal semiconductor quantum dots and π-conjugated organic molecules and polymers have attracted continuous interest in recent years, because they may find applications in bio-sensing, photodetection, and photovoltaics. Fundamental processes occurring in these nanohybrids are light absorption and emission as well as energy and/or charge transfer between the components. For future applications it is mandatory to understand, control, and optimize the wide parameter space with respect to chemical assembly and the desired photophysical properties. Accordingly, different approaches to tackle this issue are described here. Simple organic dye molecules (Dye)/quantum dot (QD) conjugates are studied with stationary and time-resolved spectroscopy to address the dynamics of energy and ultra-fast charge transfer. Micellar as well as lamellar nanostructures derived from diblock copolymers are employed to fine-tune the energy transfer efficiency of QD donor/dye acceptor couples. Finally, the transport of charges through organic components coupled to the quantum dot surface is discussed with an emphasis on functional devices.

Luminescent sensors based on quantum dot–molecule conjugates

We illustrate the principles underlying the rational construction of luminescent sensors by combining semiconductor nanocrystal and molecular components, and describe the representative examples of sensors for ionic and molecular analytes.

Supramolecular assemblies of semiconductor quantum dots and a bis(bipyridinium) derivative: luminescence quenching and aggregation phenomena

CdSe and CdSe–ZnS nanocrystal aggregates are formed in solution in the presence of a bis(bipyridinium) species, and disrupted upon addition of a macrocyclic host.