Thienoacene-fused fluorophores for highly efficient deep red/near-infrared OLEDs

Highly efficient deep red/near-infrared (DR/NIR) thermally activated delayed fluorescence (TADF) emitters were rarely reported by now, which was partially due to the lack of appropriate donor (D) and acceptor (A) units. Therefore, the exploration of novel building blocks is highly demanded for the development of efficient TADFs. Thienoacene (TA) with a ladder-type structure containing thiophene units demonstrated intriguing electronic properties. Importantly, the ring-fused system of TA lowered the lowest singlet excited state (S1) significantly and thus pushed the emission into long wavelength region. In this work, the polycyclic π-extended TA was applied to construct TADF materials (TA-TPA, TA-tBu-TPA and TA-CN-TPA), where the robust configuration resulted in high photoluminescent quantum yield (PLQY). Consequently, TADF OLED based on TA-CN-TPA demonstrated a high electroluminescence (EL) efficiency with external quantum efficiency (EQE) of 15.2% at 710 nm and 12.7% at 724 nm. This work indicated that TA-fused TADFs could exhibit attractive OLED properties, complementary to the N/O-heteroacene based emitters, and the result will pave a new path for the development of efficient heteroacene-based NIR TADFs.