The Design and Investigation of Liquid Crystal CdSe Based Quantum Dots and Nanoplates

Abstract

The electro-optical investigations of quantum dots functionalized with LC in LC matrices are the first examples of a route toward real-live technological applications for the materials I have worked for in the PhD project. The compounds have been chemically generated to fully exploit their physical and optical properties. In particular, the thesis is focused on using the advantages of LCs to guide quantum dots and nanoplates to express liquid crystalline phase behaviour. For nanoparticles (NPs), connected chemically to suitable mesogenic or dendritic groups, it was observed that LCs phase behaviour could be formed. Additionally, the last part of this work is driven by the current interest in photochromic liquid crystalline materials, with a focus on the optical properties of such materials. An azobenzene containing mesogen was synthesized and its photochromic, as well as liquid crystal properties, were investigated. In practical terms, part of the aim was to attach quantum dots to synthesized photochromic LCs and study the optical properties. Although a range of NP systems has been explored, the focus of research has so far been mainly on gold or silver-based LC NP systems, due to their excellent accessibility and the chemical stability of these materials. Surprisingly, to the best of our knowledge, there has so far been only one report on CdSe NPs which form LC phase behaviour as an example of quantum dots (QDs) linked to calamitic LC groups. It is noted, however; that there are several reports where QDs have been imported into LC mixtures. The chemical structure of the QD-LCs (quantum dot-liquid crystals) and NPL-LCs (nanoplatelets-liquid crystals) composites were characterized by proton nuclear resonance magnetic spectroscopy (1H NMR), transmission electron microscopy (TEM), UV/vis spectroscopy and thermogravimetric analysis (TGA) studies. The size of the NPs was determined by TEM characterization. Optical polarizing microscopy (OPM) and differential scanning calorimetry (DSC) was used to investigate the properties of LCs. The experimental results correlate to earlier work on conceptually related NP systems.