Boosting Triplet‐Triplet Annihilation Upconversion in OLEDs via Substituent Control in Dicarbazolyl Anthracenes

Abstract The aim of this work is the exploration of the impact of the methoxy‐, methoxyethoxy‐ and tert ‐butyl functional groups on the structure‐property relationships of the derivatives of anthracene and carbazole exhibiting triplet‐triplet annihilation (TTA) upconversion. The synthesis of three new organic semiconductors that possess tert ‐butyl, methoxy, or methoxyethoxy side groups linked via C‐3 and C‐6 positions of carbazole fragments is reported. The compounds exhibit high thermal stability with 5% weight loss temperatures in the range of 377–413 °C. The emitter with tert ‐butylcarbazole moiety exhibits a high photoluminescence quantum yield (PLQY) of 68.2%, ionization energy of 5.65 eV. The occurrence of TTA is discussed in detail, drawing on both experimental data and theoretical analysis. Organic light emitting diode based on the neat layer of the emitter shows maximum external quantum efficiency (EQE) of 3.1%. Optimization of the device structure using a host‐guest system allows to increase the EQE to 10.7%. It is shown that high EQE is a result of improved horizontal molecular alignment, TTA upconversion and high PLQY.