Versatile Thermally Activated Delayed Fluorescence Emitters via Non‐conjugated Extension Strategy Enabling OLEDs with Efficiency Over 37%

Abstract

AbstractIn recent years, thermally activated delayed fluorescence (TADF) materials with high horizontal dipole ratios (Θ//) have attracted enormous attention in constructing high‐efficiency organic light–emitting diodes (OLEDs). However, the common strategy to improve Θ// based on extending π‐conjugation tends to induce bathochromic emission shift, and emitters with Θ// exceeding 90% are rarely reported. Herein, a non‐conjugated extension strategy is developed to promote molecular horizontal dipole orientation. By simply modifying the spiro‐acridine with extra 9‐phenylcarbazole groups, two high‐efficiency and versatile TADF emitters 36DPCZSFAC‐TRZ and 36DPCZSFAC‐PYPM are constructed without bathochromic emission shift, and state‐of‐the‐art ultra‐high Θ// of 92% and 96% are achieved, respectively. More fascinatingly, due to the special spiro molecular structures, the TADF emitters hold distinguished merits of aggregation‐induced emission property, near unitary photoluminescence quantum yields, fast reverse intersystem crossing rates, and enhanced charge‐carrier transport property, which enable outstanding external quantum efficiency values of up to 22.1/20.9% and 37.4/34.2% in non‐doped/doped OLEDs for 36DPCZSFAC‐TRZ and 36DPCZSFAC‐PYPM, respectively, demonstrating their great potentials in the fabrication of high‐efficiency OLEDs.