Facile Functionalization of Ambipolar, Nitrogen-Doped PAHs toward Highly Efficient TADF OLED Emitters

Despite promisingoptoelectronic features of N-doped polycyclicaromatic hydrocarbons (PAHs), their use as functional materials remainsunderdeveloped due to their limited post-functionalization. Facingthis challenge, a novel design of N-doped PAHs with D-A-Delectronic structure for thermally activated delayed fluorescence(TADF) emitters was performed. Implementing a set of auxiliary donorsat the meta position of the protruding phenyl ring of quinoxalinetriggers an increase in the charge-transfer property simultaneouslydecreasing the delayed fluorescence lifetime. This, in turn, contributesto a narrow (0.04-0.28 eV) singlet-triplet exchangeenergy split (& UDelta;E (ST)) and promotesa reverse intersystem crossing transition that is pivotal for an efficientTADF process. Boosting the electron-donating ability of our N-PAHscaffold leads to excellent photoluminescence quantum yield that wasfound in a solid-state matrix up to 96% (for phenoxazine-substitutedderivatives, under air) with yellow or orange-red emission, dependingon the specific compound. Organic light-emitting diodes (OLEDs) utilizingsix, (D-A)-D, N-PAH emitters demonstrate a significantthroughput with a maximum external quantum efficiency of 21.9% whichis accompanied by remarkable luminance values which were found forall investigated devices in the range of 20,000-30,100 cd/m(2) which is the highest reported to date for N-doped PAHs investigatedin the OLED domain.