Mauricio Posada Urrutia: Studies in the Field of Benzo-2,1,3-thiadiazoles: Auration, Borylation, and Regioselective Substitution

Abstract

Photoluminescent materials have captivated the interest of scientists for hundreds of years. Nowadays photoluminescent materials find applications in a variety of fields as light harvesting materials, chemosensors, biological imaging agents, and more. This thesis explores the synthesis and photophysical properties of luminescent molecules derived from a central core structure of 2,1,3-benzothiadiazole. The use of a particular luminescent agent for a purpose is predicated on its specific properties. For example, bioimaging agents should not have their emission quenched in an aqueous environment. Chemosensors should have distinct spectral responses with and without analyte, and light harvesting materials should be photostable.

To this end it is imperative to understand these properties, how they can be modified, and how to chemically synthesize these luminophores in efficient and simple ways. This thesis briefly describes some common steady-state and time-resolved luminescence measurements. Some historical context as to the discovery, known chemistry, and electronic transitions of 2,1,3-benzothiadiazole is then explored. The focus is then placed on the newly synthesized and characterized compounds.

Aurated benzothiadiazole derivatives were prepared. Their steady-state and time-resolved luminescent properties were studied in solution and frozen matrices at 77 K. These compounds proved to be bright phosphors at room temperature in solution. This occurred as a function of the direct ligation of the AuI centre to the benzothiadiazole backbone. The role of the various ligands studied seemed minimal, and the luminescence was contingent on the direct connection of the heteroarene moiety to the AuI atom.

New compounds based on 2,1,3-benzothiadiazole were synthesised thanks to a methodology based on Ir-catalysed C–H activation. This methodology has made it possible to introduce boronate functionalities at classically non-reactive positions on the benzothiadiazole backbone. These new substrates paved the way for the synthesis of a scope of compounds that were mono and di-substituted (with a phenyl and methoxy substituent) in every possible arrangement. This enabled a comprehensive study of the role of substituents on the photophysical properties of the ensuing fluorophores. The placement of a particular substituent was shown to affect the radiative and non-radiative decay rates which significantly changes the luminescent efficiency of the different fluorophores—the lifetimes of the measured fluorophores varied according to the type and placement of the substituent.