New optically active nanomaterials
The area of optically active metal nanoparticles has received a great deal of attention due to the range of potential applications offered by these materials in chiral sensing, catalysis and as metamaterials in advanced optical devices . The use of stereospecific chiral stabilising molecules has also opened another avenue of interest in the area of optically active quantum dot (QD) research. Initially, optically active CdS QDs have been prepared by us using microwave induced heating with the racemic (Rac), D- and L-enantiomeric forms of penicillamine as stabilisers. Circular dichroism (CD) studies of these QDs have shown that D- and L-penicillamine stabilised particles produced mirror image CD spectra, while the particles prepared with a Rac mixture showed only a very weak signal It was also found that all three types of CdS particles (D-, L-, and Rac penicillamine) show very broad emission bands between 400 and 700 nm due to defects or trap states on the surfaces of the nanocrystals. We have also reported chiral CdSe QDs and chiral CdS nanotetrapods. All of these chiral nanostructures also showed a very broad distribution of photoluminescence which originates from emissive defect states and characteristic CD responses within the band-edge region of the spectrum. More recently we have reported intrinsic chirality of CdSe/ZnS QDs, which is caused by the presence of naturally occurring chiral defects (e.g. dislocations) and not by the presence of chiral ligands . Using theoretical modeling we have also demonstrated that optical activity can be inherent to many semiconductor nanostructures (e.g. nanowires and nanorods), as it is induced by chiral screw dislocations naturally developing during their growth. Finally, using a combination of exfoliation and phase transfer techniques, we have developed a range of optically active two dimensional (2D) nanostructures such as MoS2 and WS2. These nanostructures have demonstrated strong unique CD responses and very interesting structural morphology. It is expected that optically active nanomaterials will find a range of potential uses in the chemistry, nanobiotechnology, photonics and optical chiral chemo- and bio-sensing. In addition, optically active quantum nanostructures can find applications as circular polarized light emitters and new metamaterials.