Indexed on: 01 May '19Published on: 21 Mar '19Published in: ACS Applied Materials & Interfaces
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 ΔESTs 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 EQE of 19.1% and a narrow full-width at half-maximum (FWHM) of 44 nm, while 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 candidate to develop TADF emitters with narrow FWHMs for practical applications.