Two novel thermally activated delayed fluorescence (TADF) emitters, 3-phenylquinolino­[3,2,1-de]­acridine-5,9-dione (3-PhQAD) and 7-phenylquinolino­[3,2,1-de]­acridine-5,9-dione (7-PhQAD), were designed and synthesized based on a rigid quinolino­[3,2,1-de]­acridine-5,9-dione (QAD) framework. With the effective superimposed resonance effect from electron-deficient carbonyls and electron-rich nitrogen atom, both emitters realize significant TADF characteristics with small ΔE STs of 0.18 and 0.19 eV, respectively. And, molecular relaxations were dramatically suppressed for both emitters because of their conjugated structure. In the devices, 3-PhQAD realizes superior performance with a maximum external quantum efficiency (EQE) of 19.1% and a narrow full width at half-maximum (FWHM) of 44 nm, whereas a maximum EQE of 18.7% and an extremely narrow FWHM of 34 nm are realized for 7-PhQAD. These superior results reveal that apart from nitrogen and boron-aromatic systems, QAD framework can also act as a TADF matrix with effective resonance effect, and QAD derivatives are ideal candidates to develop TADF emitters with narrow FWHMs for practical applications.

The conformational distribution and mutual interconversion of thermally activated delayed fluorescence (TADF) emitters significantly affect the exciton utilization. However,t heir influence on the photophysics in amorphous film states is still not knownd ue to the lacko fasuitable quantitative analysis method. Herein, we used temperaturedependent time-resolved photoluminescence spectroscopyt o quantitatively measure the relative populations of the conformations of aT ADF emitter for the first time.W ef urther propose an ew concept of "self-doping" for realizing highefficiency nondoped OLEDs.Interestingly,this "compositionally" pure film actually behaves as afilm with adopant (quasiequatorial form) in am atrix (quasi-axial form). The concentration-induced quenching that may occur at high concentrations is thus expected to be effectively relieved. The "selfdoping" OLED prepared with the newly developed TADF emitter TP2P-PXZ as an eat emitting layer realizes ah igh maximum external quantum efficiency of 25.4 %a nd neglectable efficiency roll-off.