Thermally Activated Delayed Fluorescence Sensitizers As Organic and Green Alternatives in Energy-Transfer Photocatalysis

Abstract

Photocatalysis has captured the imagination of synthetic chemists and is poised to become a staple of the fine chemical industry. Over the past decade, the subfield of energytransfer (EnT) catalysis has expanded dramatically, harnessing the excited states of a photosensitizer to unlock a variety of redox-neutral, radical-based reactivities in a mild and selective fashion. However, many of the developments in this discipline rely on precious rare earth metals such as iridium. This perspective will highlight the rise of thermally activated delayed fluorescence (TADF) materials as metalfree alternatives in EnT photocatalysis for organic transformations. Emphasis will be placed on the recent progress of cycloadditions, E/Z isomerization of olefins, and other radical-initiated processes; all mediated by the mechanism of Dexter energy transfer. The tunable excited-state energetics and dynamics of TADF materials allow them to effectively compete with iridium-based sensitizers, indicating their promise as green alternatives in organocatalysis.

Imidazophenothiazine-Based Thermally Activated Delayed Fluorescence Materials with Ultra-Long-Lived Excited States for Energy Transfer Photocatalysis

“…31 These properties make organic TADF materials an attractive option for EnT photocatalysis: rapid ISC with small energy losses from S 1 to T 1 , excited state lifetimes that are tunable based on the rate of RISC, and high E T values achievable through donor−acceptor design. 21,22,29 TADF materials with deep-blue fluorescence have E T > 62.3 kcal mol −1 , making them effective sensitizers for high E T substrates. As such, TADF sensitizers such as 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) and 4,5-di(9H-carbazol-9-yl) phthalonitrile (2CzPN) have recently gained popularity at the frontiers of method development for photocatalysis (Figure 1).…”

Stacking Interactions and Photovoltaic Performance of Cs2AgBiBr6 Perovskite

“…The photocatalytic process follows a charge transfer mechanism involving the photoinduction of active species such as holes and radicals that attack nucleophilic and radical reaction sites on the substrate. Pb‐based perovskites, [ 197 ] metal complexes, [ 198 ] organic sensitizers, [ 199 ] and perovskite oxides [ 200 ] have been extensively studied for various photocatalytic applications due to their suitable photophysical properties. However, drawbacks such as instability, toxicity, and cost have plagued their application.…”

Hybrid Catalysts for Enantioselective Photo-Phosphoric Acid Catalysis

“…Furthermore, carbazolebased photocatalysts have found utility as both effective photoredox catalysts as well as highly efficient energy transfer catalysts. 16,17 On the basis of these promising features, we hypothesized that novel chiral catalysts derived from the union of chiral phosphoric acids and donor-acceptor cyanoarene-based photocatalysts would open new chemical space in both enantioselective visible light-mediated photoredox and energy transfer catalysis.…”