Synthesis of highly fluorescent tuneable boron complexes

The boron-dipyrromethene (BODIPY) dyes are without doubt the most well-known of the fluorescent boron complexes to date. With vast amounts of success seen with BODIPYs, researchinto the synthesis of novel families of heterocyclic ligands that are capable of chelating boron to produce highly fluorescent compounds is an area of expanding interest. This Thesis describes the design, synthesis of three families of heterocyclic boron complexes and characterisation of their photophysical properties. The families include boron 4,5-di(2’-pyridyl)imidazole difluoride (BODPIs), boron 2-(2’-pyridyl)pyrroles difluoride (BOPYPYs) and boron 2-(2’-pyridyl)benzimidazole diphenyl (BOPYBIs). Chapter Two highlights the synthesis of a new diverse family of boron difluoride 4,5-di(2’-pyridyl)imidazole (BODPI) dyes via a Debus-Radziszewski like condensation of 2,2’-pyridil with substituted benzaldehydes. These BODPIs exhibited excellent dye properties including large Stokes shifts, strong fluorescence in solution, solid state fluorescence, solvatochromism and a tuneable emission profile. In Chapter Three, BODPI derivatives with increased π-conjugation were prepared using two strategies and their photophysical properties were studied. The first strategy used was reacting several commercially available fused aryl aldehydes and the second was the use 2-(4”-formylphenyl)-4,5-di(2’-pyridyl)imidazole in the Knoevenagel condensation with active methylene substrates. In Chapter Four, the effect of substituents on the BOPYPY framework and their photophysical properties were studied. Symmetric, asymmetric and styryl BOPYPY exhibited strong fluorescence in both solution and solid state, solvatochromism, large Stokes shifts and are readily tuneable by the choice of the starting 1,3-diketone derivative. Chapter Five describes the preliminary study of BOPYBIs and their photophysical properties .Unlike other families described in this Thesis, BOPYBIs formed a boron complex using triphenylborane in place of boron trifluoride. The chemical and photophysical properties described in this chapter demonstrate the potential practicality of these compounds in applications such as fluorescent dyes and/or OLEDs.