Axially chiral thermally activated delayed fluorescence emitters enabled by molecular engineering towards high-performance circularly polarized OLEDs

Abstract

Circularly polarized organic light-emitting diodes (CP-OLEDs), as an emerging display technology, can meet people’s demand for higher quality of visual enjoyment. Wherein, circularly polarized thermally activated delayed fluorescence (CP-TADF) emitters has grown into a promising direction for developing efficient CP-OLEDs, however, how to synergistically advance the chirality and luminescence efficiency is still a tricky dilemma. Herein, a pair of axially chiral CP-TADF enantiomers (−)-(S)/(+)-(R)-ax-DMAC are ingeniously designed by molecular engineering to fine tune electronic and photophysical properties, achieving a major improvement in device performance while inheriting the robust chiroptical feature. Two enantiomers possess excellent TADF feature with a tiny ΔEST of 0.03 eV and high photoluminescence quantum yields (PLQYs) of 90% in doped film, which, moreover, exhibit obvious circularly polarized luminescence (CPL) signals with luminescence dissymmetry factor (|glum|) of about 2.2 × 10−3 in solution. Notably, highly efficient CP-OLEDs employing (−)-(S)/(+)-(R)-ax-DMAC as emitter radiate intense cyan CP light with the prominent maximum external quantum efficiency (EQEmax) of 30.1% and |gEL| of 2.0 × 10−3, which is the highest EQE reported among all CP-TADF emitters with axially chiral emitting skeleton. Interestingly, a remarkably and rarely high luminance of nearly 50,000 cd/m2 is reached though delicate device adjustment, and these findings indicates the collaboration of molecular engineering and sophisticated device design aid in fabricating advanced and efficient CP-OLEDs.