Controlling Photochemistry Using Molecular Switches and Upconverting Nanoparticles

Because light can be tuned, focused and has a ‘on-off’ control, the use of light to drive photolabile compounds to unmask bioactive molecules provides spatial and temporal control required to evaluate how a specific chemical species will affect the cells in living organisms and to potentially deliver therapeutiecs on demand. However, there are still questions need to be answered when using light as a tool for applications. The research described in this thesis addresses issues related to how light can be used to release small molecules from ‘masked’ forms in complex environments such as in living cells of organisms. Four inter-related questions concerning different aspects of the topic listed below are answered in the thesis. (1) How does the user know when and where the photorelease has occurred? In Chapter 2, a ‘release and report’ concept is demonstrated using a novel photolabile compound. The compound absorbs two UV photons and undergoes two sequential reactions. The first reaction releases the protected molecule and the second reaction produces a visible colour that can be conveniently monitored without any special techniques therefore the successful release process is reported.(2) How does one deliver light that is less-damaging but still capable of inducing photoreactions? And (3) How can one maintain photoreactivity of organic compounds in an aqueous environment?In Chapter 3, a ‘plug and play’ method demonstrates the simplicity of creating a water-dispersible nanosystem through co-encapsulation of hydrophobic upconverting nanoparticles and photoactive compounds by an amphiphilic organic polymer shell. More importantly, the photoreactivity of the encapsulated compounds is well maintained in aqueous medium. (4) How are unwanted photo reactions avoided? Chapter 4 decribes how to use a UV-blocking polymer shell to encapsulate upconverting nanoparticles that prevents a one-photon driven photoreaction while still allowing multi-photon driven processes. Data will be presented to show how the isomerization of diarylethenes in the assembly can be triggered by irradiation of Near-Infrared light but not by UV light or ambient light.