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

In recent years, thermally activated delayed fluorescence (TADF) materials with high horizontal dipole ratios (Theta//) have attracted enormous attention in constructing high-efficiency organic light-emitting diodes (OLEDs). However, the common strategy to improve Theta// based on extending pi-conjugation tends to induce bathochromic emission shift, and emitters with Theta// 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 Theta// 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. Two thermally-activated delayed fluorescence materials with ultra-high horizontal dipole orientation ratios of 92% and 96% are constructed without bathochromic emission shift via a non-conjugated extension strategy, and when applied to OLED devices, outstanding electroluminescent performances with maximum external quantum efficiency values of 22.1% and 20.9% in non-doped devices, 37.4% and 34.2% in doped devices are achieved, respectively.image