Synthesis and spectroscopic studies of chiral CdSe quantum dots

Abstract

Using microwave irradiation, water soluble, optically active, penicillamine (Pen) capped CdSe nanocrystals with broad spectral distribution (430-780 nm) of photoluminescence have been produced and studied by a range of instrumental techniques including absorption, circular dichroism and both steady state and time resolved photoluminescence spectroscopy. The photoluminescence of these nanocrystals is attributed to emission from surface defect states. The decay of the excited state in the nanosecond region, which can be analysed as a triple exponential, depends strongly on the emission wavelength selected, but only weakly on the excitation wavelength. Graphical Abstract: IntroductionChirality is a common occurrence in the natural world and chiraln compounds are very important in chemistry, biology, pharmacology and medicine. It has also been envisaged that chirality could play an important role in nanotechnology. 1,2 The majority of existing research in this field has been focused on chiral organic, metallorganic and biological molecules and their supramolecular structures, 3 while research in the area of chiral inorganic nanoparticles is still in the very early stage of its development. For example, there has been some work involving chiral optically active metallic gold 4,5 and silver 6,7 nanoparticles, as well as carbon nanotubes. 8,9 However, there are currently only a few recent papers dealing with chiral light emitting semiconducting nanocrystals (quantum dots). [10][11][12][13][14] In general over the last decade much attention has been directed towards II-VI type CdS, CdTe and CdSe quantum dots (QDs). [15][16][17][18][19] It is the ability to fine-tune their optical properties by chemical control of their size and shape (i.e. their degree of quantum confinement) which makes quantum dots particularly interesting. This level of optical control combined with QDs' resistance to photobleaching and their high level of solubility in practically any solvent (depending on the stabiliser used) make these nanomaterials potentially suited for roles as divergent as light emitting diodes, 20 biological sensors 21 and photovoltaic devices. [22][23][24] Thiol group containing amino acids have proved to be excellent stabilisers, with L-cysteine becoming one of the popular surface capping molecules for CdX (X ¼ S, Se, and Te) nanoparticles. 18,[25][26][27][28][29][30][31] In addition this use of stereospecific chiral stabilising molecules opened another avenue of interest in the area of quantum dot research, as chirality is a key factor in biological and biochemical interactions. Due to their unique photophysical properties, we believe that chiral QDs have a range of potential applications in photonics and biochemistry. 13,32,33 The main aim of our work is to develop novel chiral CdSe based QDs by using chiral stabilisers and to investigate the properties of these materials. Here we report the synthesis and detailed spectroscopic studies of new penicillamine stabilised CdSe QDs, which have been prepared using the dextrorota...

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.…”

Surface Modification of CdSe and CdS Quantum Dots-Experimental and Density Function Theory Investigation

“…It is difficult to reproducibly apply chemical and biochemical procedures to these QDs because of their unstable nature. In addition to the use of thiol molecules to cap the surfaces of CdSe QDs, most researchers used various amines as ligands to modify the optical properties of CdSe QDs [40][41][42][43][44]. Talapin et al synthesized CdSe QDs in a three-component hexadecylamine (HDA)-trioctylphosphine oxide (TOPO)-trioctylphosphine (TOP) mixture [35].…”