Chiral luminescent CdS nano-tetrapods

Abstract

The utilisation of chiral penicillamine stabilisers allowed the preparation of new water soluble white emitting CdS nano-tetrapods, which demonstrated circular dichroism in the band-edge region of the spectrum.Semiconductor nanocrystals or quantum dots are remarkable for their size dependent optical and photonic properties, which differ significantly from the bulk material. These unique properties are of great interest for a number of potential applications including biomedical imaging, 1-4 sensing, 5 light-emitting diodes (LEDs), 6 photovoltaics 7 and displays. 8Previously the preparation of new chiral quantum dots which demonstrate circular dichroism (CD) activity was achieved by the microwave synthesis in the presence of the chiral penicillamine stabiliser. 9 In this case the formation of chiral defects in the nanocrystals structure leads both to the defect emission and CD response. 10 More recent reports on chiral CdTe based nanoparticles have also been published. 11,12 There is also a very recent theoretical work, which demonstrated that the electric field of the metal or semiconductor nanoparticle enhances the signal from the chiral stabiliser and other chiral species.13 Chirality is a common occurrence in the natural world and chiral compounds have very important applications in chemistry, biology, pharmacology and medicine. Therefore chiral nanoparticles have been envisaged to play an important role in science and technology. 14,15 In particular CD active luminescent nanoparticles have a great potential for the development of new chiral nanosensors.Over last years there have also been several reports on semiconductor nanomaterials with tetrapodal morphology. These amazing nanostructures have been of great interest due to their potential use in photovoltaics, 16 in the synthesis of asymmetric nano-assemblies 17 as well as prospective additives for polymer reinforcement.18 These materials have also displayed anisotropic emission 19 as a direct result of their morphology. Normally the synthesis of nanotetrapods 18,[20][21][22][23][24][25][26][27][28][29] involves the use of high temperature organic phase reactions or the utilisation of solvothermal approach. The mechanism proposed for the formation of these structures 23 engages the generation of seed nanocrystals that subsequently act as sites for preferential growth of the arms. Evidence for this mechanism may be found in the production of heterostructures using prepared pre-formed seed of one material followed by the use of additional materials to grow the arms. 28,30Here we report new chiral CdS nanotetrapods, which have been produced by heating of a basic aqueous solution of CdCl 2 , thioacetamide and racemic (Rac), D-or L-enantiomeric forms of penicillamine (Pen) under reflux.z Samples of the products have been diluted and examined using UV-VIS and photoluminescence (PL) spectroscopy to analyse the absorbance and emission characteristics of the samples. The absorbance spectra show a defined band edge at approximately 370 nm for both enantiomers of the...

Spin Selective Charge Transport through Cysteine Capped CdSe Quantum Dots

“…Since then, the chiroptical behavior of QDs has been demonstrated for different ligand stabilizers (cysteine, glutathione), other semiconductors (CdSe and CdTe), different synthetic routes (solution phase techniques and ligand exchanged from its native achiral ligand to a chiral one), and different QD shapes (tetrapods, rods). 25,27,28,29,30,31,32,33 Here, chiral cysteine passivated CdSe QDs are synthesized and their spin dependent charge transport properties are measured using magnetic conductive probe atomic force microscopy (mCP-AFM) and magnetoresistance (MR) measurements. The findings from this 4 study show that the individual QDs and the QD films act as spin filters.…”

Plasmon-induced CD response of oligonucleotide-conjugated metal nanoparticles

“…We also note that chiral CdS and CdSe nanoparticles have been previously reported but in these nanostructures the chirality and emitting properties were induced by chiral surface defects. [22][23][24][25] An important observation in this study is that the plasmoninduced CD band (500-700 nm) appears for aggregated nanocrystals of very different geometries (NPs and NRs). This observation is consistent with the Coulomb hot-spot mechanism since plasmonic hot spots will appear in both NP and NR systems.…”

Compact and highly stable quantum dots through optimized aqueous phase transfer

“…4 illustrates that the Pen-functionalized quantum dots retain the chiral character of the capping molecules and exhibit a modified CD spectrum as compared to pure D-penicillamine. Gun'ko and coworkers synthesized chiral quantum dots in the presence of D-or L-penicillamine [11,12]. CD active luminescent nanocrystals are believed to have a high potential for the development of new chiral nanosensors.…”