Synthesis and Characterization of Azo bispyrroles

Abstract

Azo dyes are a class of chromophores that can be tuned to access the entire visible range. This characteristic makes azo dyes highly attractive for uses in colouring, and today they account for the majority of industrial dyes. Azo dyes often have the capability to photo-switch (E- to Z-isomers), making them desirable in bio-medical applications. Although the literature on azo benzenes is extensive, research focusing on heteroaryl azo dyes is under-explored. Among all heteroaryl dyes, azo bispyrroles have not been reported. This thesis discusses the isolation and characterization of eight azo bispyrroles. Chapter 1 discusses the synthesis and isolation of azo bispyrroles using sterically bulky nitrobutanones as starting materials. These steric features promote the formation of azo bispyrroles over aza-dipyrrins and optimized synthetic and purification methodology was developed. Chapter 2 describes the photophysical characterization of azo bispyrroles. With efforts to explore photoisomerization of azo bispyrroles, it was found that the relative stability in non-anhydrous solution was poor as these compounds readily decompose in the presence of light. However, studies with anhydrous solutions of azo bispyrroles showed improved stability under the same conditions, yet no photoisomerization was observed. Studies involving azo bispyrroles in their solid-state resulted in the first evidence of a PSS, and thereby evidence for photoisomerization of an azo bispyrrole.