Nano-optical Control of Chiral Photochemistry
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Typ
Examensarbete för masterexamen
Master Thesis
Master Thesis
Program
Nanotechnology (MPNAT), MSc
Publicerad
2019
Författare
Larsson, Wera
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Many active compounds in pharmaceutical drugs are chiral, meaning that they consist of molecular forms that cannot be superimposed into one another. The different chiral forms are called enantiomers, and the pharmaceutical properties of the different enantiomers can vary extensively. One of the major challenges within the pharmaceutical industry when it comes to cost-effective manufacturing of safe and effective pharmaceutical drugs is therefore to produce medicines consisting of only one enantiomer, so called enantiopure compounds. Today, the chiral synthesis of enantiopure compounds is mainly done by using complicated and expensive methods within advanced organic chemistry. This thesis proposes a new physical approach to chiral synthesis, which is both cheaper and less complicated compared to the methods used today. In order to test this approach, a model system based on the chiral photochemical reaction of a model prochiral molecular photoswitch is used. The photoswitch is a derivative of dithienylethene (DTE) called DTE-1, and it undergoes a reversible phototransformation between an achiral and a chiral form commonly called the ’open’ and ’closed’ forms respectively. The two enantiomers in the closed form have a different ability for absorbing left and right circularly polarized light (LCP and RCP light), but this difference is most often not enough to create a considerable enantiomeric excess of one or the other enantiomers by only illuminating them with LCP or RCP light. Optical plasmonic nanoantennas, which are antennas that can manipulate (i.e. receive and transmit, modify its polarization etc.) light on the nanoscale, are designed and fabricated to have an enhanced chiral optical near-field. Experimental characterization methods involving circular dichroism (CD) spectroscopy has together with numerical simulations indicated that the fabricated nanoantennas have the desired properties. By placing the DTE-1 molecules in a close proximity of the nanoantennas and illuminating with non-polarized light of the wavelengths that trigger the photochemical reaction, the aim is for the enhanced near-field to induce an enantiomeric excess at phototransformation. According to the results presented in this thesis, this is achieved for two samples made up of spiral shaped aluminium nanoantennas. Reproducibility of both the fabrication and chiral synthesis was not possible to prove within the time frame of this thesis, and is something that needs to be considered in order to draw final conclusions. Even though there still is an extensive amount of work needed before the proposed approach could be used within the pharmaceutical drug development process, this thesis paves the way towards this vision.
Beskrivning
Ämne/nyckelord
Fysik , Physical Sciences