The applications of interaction between light and chemical reactivity in molecular systems

This thesis presents a series of scientific examples that provide further insight into the connection of light and chemical reactivity for applications in catalysis, targeted drug delivery, and detection. Small organic molecules based on 1,2-dithienylethenes (DTEs) and noble metal-based nano-assemblies were incorporated into the system to impart control over their physical and chemical properties, and activity. The light was used as an external stimulus to initiate chemical reactions by causing either a structural, electronic, or chemical change in the chromophore or energy transformation (such as heat) in the system. In the first example (Chapter 2), light is employed to generate the variation in the activity of Karstedt's catalyst by introducing a DTE-based inhibitor. It is demonstrated that the electronic changes that occur during the light-assisted isomerization of dithienylethene lead to changes in the binding strength of the inhibitor to the catalyst's metal centre. This, in turn, leads to changes in the reaction progression of simple hydrosilylation reactions. In the second example (Chapter 3), a novel dual-mode (colourimetric and fluorescent) optical probe based on photoresponsive dithienylethene is developed for fast and user-friendly detection and consumption of hydrazine in the vapour and solution phase. The molecule reacts with hydrazine to induce an irreversible structural change in the 1,3,5-hexatriene system leading to deactivation of photochromic activity by quenching effects and simultaneously generating an emissive response. In the third example (Chapter 4), light is used as an external stimulus to indirectly gate the chemical reactivity for an on-demand release of therapeutics in aqueous environments by creating nanoassemblies based on gold nanoparticle core. The constructed nanoassemblies consist of the thermoresponsive Diels-Alder adducts of the molecules to be released close to gold nanoparticles enclosed in an amphiphilic polymer shell. The system uses the photothermal effect of gold nanoparticles to trigger thermo-responsive retro Diels-Alder reactions in the vicinity of nanoparticles to release therapeutic molecules in aqueous solutions.