Photoswitchable dyes for super-resolution microscopy

This thesis describes the synthesis and characterisation of photoswitchable synthetic dyes for application in super-resolution microscopy of biological systems. Chapter 1 introduces the field of super-resolution microscopy. A variety of techniques are described, with a particular focus on the reversible saturable optical fluorescence transitions (RESOLFT) approach. For RESOLFT application, a dyad molecular design is proposed, which comprises a reversible photoswitch and an emissive dye. Major classes of these components are presented, followed by a discussion of the criteria required for RESOLFT dyes. Chapter 2 reports preparation of spiropyran photoswitches and a derived dyad. Properties of the switches are characterised, including photoconversion and resistance to photodegradation. The dyad system is also examined by live cell confocal imaging. Chapter 3 focuses on switches from the spirooxazine family that is closely related to the spiropyran family. Synthesis and crystal structure are described, and detailed examination of the photoswitching behaviour by spectroscopic measurements is then presented. Subsequent switching kinetic investigations using ultrafast spectroscopies are reported. Chapter 4 continues to describe a series of spirooxazine-based dyads. Their switching behaviour is assessed in live cells, and the applicability in RESOLFT microscopy is also tested. The photophysical properties of these dyads are comprehensively characterised and compared, providing insights into the molecular design for future work. Chapter 5 explores the possibility of selectively labelling biomolecules of interest by incorporating bioconjugation techniques into the dyad design. Several synthetic approaches led to a series of compounds, and comparison of their cell images suggests key factors for further considerations. Chapter 6 demonstrates the RESOLFT potential of the dyad in liposomes. The switching behaviour is investigated in different types of liposomes, and detailed imaging analyses are reported, highlighting the varying performance of the dyad in different systems. Chapter 7 summarises the conclusions described in this work.