Molecular engineering of locked alkyl aryl carbonyl-based thermally activated delayed fluorescence emitters via a cascade C-H activation process.

While diaryl ketones have drawn tremendous attention for the assembly of carbonyl-based thermally activated delayed fluorescence (TADF) emitters, alkyl aryl ketones are almost ignored. In this work, an efficient rhodium-catalyzed cascade C-H activation process of alkyl aryl ketones with phenylboronic acids has been developed for the concise construction of the α,α-dialkyl/aryl phenanthrone skeleton, which unlocks an opportunity to rapidly assemble a library of structurally nontraditional locked alkyl aryl carbonyl-based TADF emitters. Molecular engineering indicates that the introduction of a donor on the A ring enables the emitters to exhibit better TADF properties than those with a donor on the B ring. 2,6-Bis(9,9-dimethylacridin-10(9H)-yl)-10,10-diphenylphenanthren-9(10H)-one (2,6-DMAC-DPPO) with two donors on the A and B rings gives rise to superior organic light-emitting diode (OLED) performance with maximum external quantum efficiency and power efficiency as high as 32.6% and 123.5 lm W-1, respectively.