The Synthesis and Photophysics of Cyclometalated Iridium Complexes and Photochromic Materials

Abstract

This thesis concerns two main themes: cyclometalated iridium complexes and organic photochromic materials. The presentation of the work has been split into two parts regarding these distinct topics, each having an introduction, discussion of results and suggestions for future work, followed by a combined experimental section.

Chapter 1 provides a general introduction to the photophysical concepts relevant to the whole thesis. Following this is an overview of cyclometalated iridium complexes, their synthesis, photophysical properties and applications. At the end of this chapter, palladium-catalysed cross-coupling reactions are reviewed due to their importance in preparing many of the materials described.

In Chapter 2, the results from the work conducted on cyclometalated iridium complexes are discussed. Tris-heteroleptic cyclometalated iridium complexes of the form [IrLL′(acac)] are first described. The synthesis of several examples of this class of complex and their photophysical properties are summarised, supported by theoretical calculations. A detailed study of the isomeric iridium complexes having 1- and 2-(2′-pyridyl)pyrene ligands is then presented, including a discussion of their syntheses, photophysics and electrochemistry as well as an evaluation of some TD-DFT methods for the accurate calculation of optical transitions. Subsequently, the time-gated two-photon spectroscopy of Ir-Eu and Ir-Tb dyads is demonstrated. Concluding this chapter is a discussion of the synthesis of a tris-heteroleptic iridium complex bearing a terminal acetylene substituent that is a divergent intermediate to further complexes having π-extended ligands. A photophysical and theoretical investigation of some derivatives synthesised by direct Sonogashira coupling of this intermediate is presented.

Chapter 3 introduces photochromism and provides an overview of some of the more common classes of molecules that exhibit this phenomenon. More specific detail is then given about the triphenylimidazolyl radical (TPIR) and dihydropyrene (DHP) systems that feature in Chapter 4.

Chapter 4 details the findings from the work conducted on the aforementioned TPIR and DHP photochromic materials. This includes the identification of a peroxide fatigue product of TPIRs and the isolation of a normally unstable dimerisation mode of a TPIR derivative by application of the photocrystallisation method. Attempts to synthesise DHP derivatives, and the associated challenges, are then described.

Finally, Chapter 5 contains the combined experimental detail and synthetic procedures for the work described in the previous chapters.