Synthesis of functional organic dyes and their characterization using NMR, MS, UV-vis and fluorimetry

Abstract

Organic dyes have been one of the most important areas of research in the last decade. Although they are mainly used in electronics, such as in OLED displays, they have opened up new opportunities for research in photocatalysis and molecular sensing. Despite the fact that photoredox catalysis is a relatively new method in organic synthesis, many studies have demonstrated its usefulness, especially when combined with other types of catalysis. Dual catalytic reactions that combine photocatalysis and transition-metal catalysis are of great interest in synthetic organic chemistry. However, these reactions often suffer from low quantum yields (QYs), especially for reductive reactions using Hantzsch esters (HEH) as reducing agents. This latter mentioned type of reactions undergoes a key intermediate complex ([PC-HEH]) that experiences a charge recombination process when it reacts with the transition metal. For this reason, currently, the use of reductive reactions using HEH is limited to academic interests. Thus, the aim of this project is to synthesise and characterise a photocatalyst containing an N3 group that will allow us to pre-organise ground state [PC-HEH] complexes via 'click' chemistry. This will increase the quantum yield of these reactions, making them scalable. Therefore, two synthetic routes were followed to synthesise the two targeted photocatalysts. On the one hand, in the first synthetic route, 3CzFINP (2) and 3-azido-9H-carbazole (4) have been successfully synthesised. On the other hand, three out of seven steps of the synthesis were completed, resulting in the successful synthesis of tert-butyl-3-bromo-9H-carbazole-9-carboxylate (7), 3-formyl-9-tert-butoxycarbonyl-9H-carbazole (8) and tert-butyl-3-(hydroxymethyl)-9H-carbazole-9-carboxylate (10). Alongside these latter, tert-butyl 3-(((tert-butyldimethylsilyl)oxy)methyl)-9H-carbazole-9-carboxylate (11) has also been synthesised after protection of 10. All compounds synthesised by both synthetic routes were characterised by standard techniques such as 1H NMR, 13C NMR, IR and MS spectroscopy.