Donnelly, Joanna Louise; (2020) Design, Synthesis and Application of Light-activated Tools for Chemical and Biological Research. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Chromophores are fundamental tools for chemical and biological research and are readily applied in many aspects of life and material science. Their applications are broad and illustrate the diversity and importance of light-activated tools in a variety of scientific fields. The applications of fluorophores include diagnostics, biological discovery, biomedical research and as sensitizing dyes for photovoltaic devices. There is increasing demand for chromophores with highly specific optical properties. Meeting these demands can improve the performance of chromophores for a variety of applications. A classic example of this is long wavelength photon absorption and emission. This is predominantly due to the strong compatibility of infra-red light with biological tissue. The intricacies of biological events can be monitored safely and accurately using target specific fluorophores that are activate within the biological optical window; this is typically above 600 nm. Other highly desirable characteristics of long wavelength fluorophores include solvatochromism, environmentally dependent fluorescence emission, target specificity and non-cytotoxicity. In addition, sensitizing dyes active at longer wavelengths promote faster electronic recombination, thus improving the power conversion efficiency of photovoltaic devices. There is a consequential impetus to design chromophores with finely and reliably tuneable photophysical properties that can be applied as specialized lightactivated tools. Designing chromophores with these desirable properties requires a detailed understanding of the structure activity relationships (SAR) between chromophore design and photophysical properties. A series of 17 organic chromophores built around the BODIPY molecule have been designed and synthesised to address these demands. Functionalisation has been carried out at three different positions of the BODIPY molecule, with substituents ranging in steric bulk, polarity and electronic effect. Photophysical profiles have been determined including absorption and emission spectra, alongside computational modelling to establish molecular orbital stabilities. From these data, correlation between substituents and loci on the BODIPY construct, and resultant photophysical properties and application potential has been established. Establishment of structural activity relationships enables fine-tuning of spectral properties to facilitate the development of specialised chromophores able to meet specific application demands. Long wavelength chromophores with environmental sensitivity can be applied in several applications. The designed BODIPY analogues have been successfully applied for target-specific bio-imaging of lipophilic membranes. The “switch-on” fluorescence enables visualization of lipid membranes with good signal-to-noise ratio, with biocompatibility and low cytotoxicity. A fluorophore integrating all desirable properties is expected to drive bio-imaging of cells, tissues and organisms to facilitate detection, observation and control of biological systems, and promote research and diagnostics. The photophysical profiles of some of the analogues also allows them to perform as sensitizing dyes in dye sensitized solar cells (DSSCs). This has been undertaken successfully using two of the generated analogues.

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