Donor-acceptor thermally activated delayed fluorescence (TADF) chromophores: photocatalysis and photochemical mechanism

This thesis explores donor-acceptor-based TADF (Thermally Activated Delayed Fluorescence) compounds for their potential as photocatalysts (PCs), with a focus on chromophore design, photophysical and electrochemical properties, and photoreaction mechanisms. Chapter 1 outlines the fundamental characteristics of TADF, the key concepts essential for understanding TADF photocatalysis, and its fields of application. Chapter 2 investigates the photophysical properties of a TADF emitter, pDTCz-DPmS, developed by the Zysman-Colman group at the University of St. Andrews, UK. The study examines its photocatalytic role in a C-C bond-forming reaction, specifically the decarboxylative addition of protected proline to diethyl maleate. This research underscores the importance of comprehending reaction mechanisms to enhance and optimize efficiencies in diverse photocatalytic systems. Chapter 3 focuses on a carbazole-1,3-dicarbonitrile derivative obtained from the photoconversion of 3DPAFIPN. This compound, proven to be a TADF emitter, exhibits distinct photophysical properties and catalytic potential. It was applied in photoredox-mediated catalysis with a Co(II) species by the Cozzi group at the University of Bologna, Italy. The reaction mechanism is thoroughly analyzed in this thesis. Chapter 4 examines the formation and consumption of radical anions of 4CzIPN under photoredox conditions. Misconceptions regarding the absorption and emission profiles of 4CzIPN˙⁻ are addressed, along with its assumed role in strong photoreduction reactions. Chapter 5 explores the applicability of donor-acceptor TADF emitters, initially developed for OLEDs, as photocatalysts in various reactions. Their unique redox and photophysical properties are discussed, with solvent choice playing a significant role in optimizing reaction yields. Chapter 6 introduces a new series of dicyanoarene-cored persulfurated chromophores. Their synthesis, photophysical and electrochemical characterization, and application in photocatalysis are examined. Structural modifications enhanced charge transfer properties, red-shifted emissions, and visible light absorption, showcasing the versatility of these chromophores. This comprehensive study provides valuable insights into the design and optimization of TADF emitters for advanced photocatalytic applications.