Photophysical Studies of the Doublet Excited States of Donor-Acceptor Chromophore Radical Anions in the Application of Photocatalysis
Photocatalysis has been a continuously growing field that has a constant demand for stronger redox agents, especially those that can absorb in low-energy visible and/or near-infrared (NIR) regions since it allows for even more significant applications across scientific fields. Current research has focused on the approach of mimicking the photosystems of green plants and cyanobacteria, which use low-energy solar photons, by developing electron donor-acceptor systems. Radical ion excited doublet states of such system provide another promising approach in the search for chromophores capable of acting as photo-driven redox agents with low-energy photons. Herein, I describe the photophysical properties of a series of donor-acceptor (DA) and donor-acceptor-donor (DAD) systems in their 1-electron reduced state with the aim of searching for super-reductants for viable photocatalysis applications. In this report, the target molecules and complexes were thermally reduced by naphthalene radical anion (Naph•-) reducing agent. The newly formed radical anions were then analyzed by a series of spectroscopy techniques to study their doublet excited-state photophysical properties. First, several imide-functionalized rylene dye derivatives were investigated, including a benzodmaphthalene diimide (BDI) and a naphthalimide (NI) chromophore. Secondly, I expanded the study to a series of electron donor – electron acceptor (DA) systems, in which the acceptor NI was coupled with different donors, such as oligo(phenylene ethynylene)s (OPEs) and thiophene/thienylene (Ts) with varying chain lengths. Furthermore, I carried out the studies on two different series of DAD chromophores: (1) benzothiadiazole was employed as the acceptor moiety, and the donors were varied; (2) thiophene moiety was kept as the electron donor, and the acceptors were different arylene moieties. Finally, the research was further expanded to Platinum-incorporated complexes and polymer in an attempt to observe the effect of spin-orbit coupling on the doublet excited-state photophysical properties of these chromophores.