cis/trans ‐Through‐Space Charge‐Transfer Isomers Enabled by Acceptor Fusion for High‐Efficiency Thermally‐Activated Delayed Fluorescence and Circularly Polarized Emission

ABSTRACT Multi‐π‐stacked through‑space charge‑transfer (TSCT) emitters have shown great potential for developing efficient thermally‐activated delayed fluorescence (TADF) toward organic light‑emitting diodes (OLEDs) applications. New design paradigms are highly demanded for constructing multi‐π‐stacked TSCT‐TADF emitters, especially the chiral ones with chiroptical activity. Herein, by fusing the acceptors of two single π‐stacked TSCT units, cis / trans isomeric multi‐π‐stacked TSCT emitters ( cis ‐2D/A and trans ‐2D/A ) are developed. The trans isomer exhibits intrinsic chirality and exists as a pair of enantiomers, ( R , R )‐ trans ‐2D/A and ( S , S )‐ trans ‐2D/A . In doped films, cis ‐2D/A and trans ‐2D/A exhibit green TADF with largely accelerated radiative decay, and ( R , R )/( S , S )‐ trans ‐2D/A display circularly polarized emission. OLEDs based on cis ‐2D/A and trans ‐2D/A show maximum external quantum efficiencies (EQE max ) of around 27.0% and largely suppressed efficiency roll‐offs. The devices based on ( R , R )/( S , S )‐ trans ‐2D/A further exhibit circularly polarized electroluminescence with electroluminescence dissymmetry factors at around ±1.2 × 10 −3 . Narrowband OLEDs employing cis ‐2D/A and trans ‐2D/A as sensitizers show high EQE max up to 37.0% and EQEs at 1000 cd m −2 up to 30.2%. The devices employing ( R , R )/( S , S )‐ trans ‐2D /A as chiral sensitizers further exhibit circularly polarized narrowband electroluminescence with electroluminescence dissymmetry factors at around ±2.3 × 10 −3 , which rank among the most efficient circularly polarized narrowband OLEDs reported so far.