Exploring applications of O-BODIPY complexes: sugars and cobaloximes

Abstract

F-BODIPYs (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) are widely used fluorescent dyes. They are typically appended to the analyte or target through modification on the dipyrrin framework, leaving the BF2 core intact. The ability to substitute the fluorines in F-BODIPY by more labile Cl or O substituents offers the possibility of developing a new approach to incorporating the fluorophore into functional chemical systems. This project explores two applications of O-BODIPYs functionalized at the boron atom. The first application describes the potential of O-BODIPY as a fluorescent probe for saccharide detection, building on a preliminary report which combined the characteristics of both the fluorescent O-BODIPY labels and the sugar-binding of boronic acids and developed a new class of glucose-O-BODIPY conjugates. The second application describes the use of O-BODIPY as the photosensitiser in a cobaloxime-containing system for photocatalytic hydrogen production. The cobaloxime is modified by insertion of BODIPY into the ligand framework where it is covalently attached through two oxygens of the oxime groups. Chapter 1 is an introduction to F-BODIPY and its derivatives, sugars, and the most commonly used sugar sensors in the literature. This chapter also discusses the newly developed transesterification methodology, which is used for the synthesis of sugar-O-BODIPY conjugates in the subsequent chapters. Chapter 2 reports the activation of F-BODIPY by BCl3 to produce Cl-BODIPY, which on treatment with MeOH yields MeO-BODIPY, which has proved to be the best precursor to sugar-O-BODIPY conjugates. The methodology for the preparation of pentose-O-BODIPY conjugates incorporating ribose and xylose is discussed, along with the full characterisation of the products which exhibit 1:1 and 1:2 pentose:BODIPY ratios and contain the pentose in different (furanose/pyranose) forms and measurement of their photophysical properties. Chapter 3 extends the reaction of MeO-BODIPY to different hexoses to prepare hexose-O-BODIPY conjugates containing glucose, fructose, galactose and mannose. The full characterisation and photophysical properties of the conjugates, which show 1:1, 1:2 and 1:3 hexose:BODIPY ratios and involve the hexose in furanose/pyranose forms, are discussed. Chapter 4 discusses the synthesis and characterisation of disaccharide-O-BODIPY conjugates which were investigated for sucrose, maltose, lactose, trehalose and cellobiose. Adaptation of the methodology for the more polar disaccharide conjugates resulted in the choice of DMF as the solvent and reversed-phase HPLC for purification. Chapter 5 begins with a brief introduction to the cobalt catalysts and cobaloxime-O-BODIPY based photocatalytic systems. The synthesis of the cobaloxime-O-BODIPY conjugate via Cl-BODIPY, its full characterisation and preliminary results on photocatalytic hydrogen production are discussed. A second catalyst, cobalt diimine-dioxime is also prepared to form an overall charged complex with BODIPY, designed to be more soluble in water. Chapter 6 presents an overall summary of the thesis.