The design, synthesis and application of 4,7-Diarylbenzo[c][1,2,5]thiadiazole photocatalysts

Abstract

The debate surrounding climate change and global resource consumption has stimulated discussion within the chemical community about sustainable methods for enabling chemical transformations. Among the various avenues of research, photocatalysis has been identified as an attractive sustainable option as it would allow society to make use of light as an abundant resource that is not environmentally damaging. Current state of the art photocatalysts tend to be based on iridium and ruthenium polypyridyl complexes. However, the cost and low natural abundance of the metals they contain is not compatible with the long term environmental sustainability that modern photocatalysis is striving towards. Organophotocatalysts have been identified as a promising solution to this problem as they are derived from more abundant chemical feedstocks, making them far cheaper to synthesise and allowing for better long-term sustainability. In addition to natural pigments and organic dyes, various organic π-conjugated electron donor-acceptor (D-A) systems, comprising of electron-rich donor and electron-deficient acceptor groups connected through delocalised π-conjugated structures, have been investigated as organophotocatalysts. The benzo[c][1,2,5]thiadiazole (BTZ) group is an example of a strongly electron withdrawing group that has mainly been researched for photovoltaic systems although some promising photocatalysis has already been investigated with this moeity. Four different methods for utilising BTZ photocatalysts are presented in this thesis. The first of these was a conventional homogeneous approach to photocatalysis, whereby a series of structurally similar molecular BTZ photocatalysts were synthesised to optimise their photophysical and optoelectronic properties towards a test photoredox reaction. Secondly, photocatalysts were appended to the upper-rim of calix[4]arenes to investigate using their ability to form host-guest complexes to facilitate photocatalysis. The third and fourth regimes involve the use of two different polymer systems by either chemically incorporating the BTZ group into conjugated porous polymers or by trapping molecular photocatalysts within solution cast thin films of intrinsically microporous polymers.