Fundamentals of Photochemistry: Excited State Formation/Deactivation and Energy Transfer Processes

Intramolecular locking and coumarin insertion: a stepwise approach for TADF design

“…26 Starting from 4-chloro-3nitro-2H-chromen-2-one the chlorine group was first substituted for an amine and then the nitro substituent was reduced (Scheme 1). Thereafter, a condensation reaction between the diamines and the 'locked' or 'unlocked' diketone yielded the desired brominated coumarin-quinoxaline products (3)(4)(5)(6). The brominated acceptor units were then coupled to 9,10-dihydro-9,9-dimethylacridine (DMAC) using a Buchwald-Hartwig crosscoupling reaction, affording Qx-Ph-DMAC, BQx-Ph-DMAC, ChromPy-Ph-DMAC, and DBChromQx-DMAC.…”

“…Thermally activated delayed fluorescence (TADF) emitters have gained significant attention as active materials for organic light-emitting diodes (OLEDs) as they can harvest both singlet and triplet excitons, realizing theoretical internal quantum efficiencies (IQE) up to 100%. [1][2][3][4] In contrast to the strong spin-orbit coupling (SOC) that enables phosphorescence in organometallic emitters, 5,6 high IQEs for all-organic TADF materials are achieved by reverse intersystem crossing (rISC), up-converting the 75% of triplet excitons arising from electrical excitation to the emissive singlet excited state. [7][8][9][10] Typically such TADF materials consist of covalently linked electrondonating (D) and electron-accepting (A) units that have nearperpendicular electronic subsystems, spatially limiting the overlap of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) and generating a small energy difference (DE ST ) between the first excited singlet (S 1 ) and triplet (T 1 ) state, which allows the desired rISC up-conversion to occur.…”