The synthesis of rationally designed donor-acceptor dyads incorporating the boron dipyrromethene fluorophore

Abstract

This thesis is concerned with the design, synthesis, characterisation and subsequent photophysical examination of dyads incorporating the boron dipyrromethane (bodipy) framework. Photodriven processes such as electron-, energy- and charge-transfer reactions are of the utmost importance in nature, with photosynthesis as a key example. Energy capturing arrays composed of intricate building blocks trap, transfer and store energy within a cell, employing a complex series of cascade-type reactions to channel this energy to the desired acceptor. Within this thesis, the theme of charge-transfer in particular is of principal focus and systems designed to investigate this phenomenon are examined. Chapter one presents an introduction to the bodipy fluorophore and the everexpanding field of artificial photosynthesis. In addition to this, the methods involved in analysing the distribution and movement of charge are discussed, as are the thought processes behind the rational design of molecules for specific functions. The second chapter serves as a detailed account of all the synthetic procedures undertaken. The chapter covers all the bodipy derivatives prepared, in addition to the precursors to these compounds and all additional materials synthesised. In chapters three to six, the rationale behind the design of each purpose built system is discussed, along with any preparative difficulties encountered and modifications to traditional synthetic protocol. Finally, the electrochemical properties of the compounds are analysed by cyclic voltammetry and their photophysics investigated by absorption and fluorescence spectroscopy. The data obtained is complimented by both appropriate NMR spectra and a discussion of crystal structural information obtained. In the case of the novel push-pull chromophore, JULBD, which is the principal focus of chapters three and four, the charge transfer capabilities of the dyad are analysed by correlating 13C chemical shift values with solvent polarity. This polarity dependence is further explored and analysed by solvent dependent absorption spectroscopy. In ii order to study the emissive properties, a temperature dependent fluorescence experiment was undertaken. Chapter five discusses the use of current catalytic methods to prepare a series of novel donor acceptor dyads and their precursor building blocks, introducing novel methodology for the synthesis of boronic esters including iridium and palladium catalysis. Finally, chapter six addresses the design rationale, synthesis and characterisation of a binaphthalene-spaced dyad incorporating the N,N-dimethylaniline moiety. This chapter also serves to introduce novel methodology which can be employed to execute bodipy sythesis employing the commonly used organic reagent formamide.