Thermally Activated Delayed Fluorescent Donor–Acceptor–Donor–Acceptor π‑Conjugated Macrocycle for Organic Light-Emitting Diodes

A new
class of thermally activated delayed fluorescent donor–acceptor–donor–acceptor
(D–A–D–A) π-conjugated macrocycle comprised
of two U-shaped electron-acceptors (dibenzo­[a,j]­phenazine) and two electron-donors (N,N′-diphenyl-p-phenyelendiamine)
has been rationally designed and successfully synthesized. The macrocyclic
compound displayed polymorphs-dependent conformations and emission
properties. Comparative studies on physicochemical properties of the
macrocycle with a linear surrogate have revealed significant effects
of the structural cyclization of the D–A-repeating unit, including
more efficient thermally activated delayed fluorescence (TADF). Furthermore,
an organic light-emitting diode (OLED) device fabricated with the
macrocycle compound as the emitter has achieved a high external quantum
efficiency (EQE) up to 11.6%, far exceeding the theoretical maximum
(5%) of conventional fluorescent emitters and that with linear analogue
(6.9%).