Phenothiazine dioxide end-capped spiro[fluorene-9,9′- xanthene] as host for efficient blue TADF OLEDs

A spiroconfigured phenothiazine dioxide compound 10-(2- spiro [fluorenyl-9,9′-xanthen])-phenothiazine 5,5-dioxide (SFX-PzO₂) was successfully synthesized via C–N cross-coupling with Pd(PPh₃)₄ as a catalyst, to set up the state-of-the-art models of spiroconfigured phenothiazine dioxide-based small molecular host, which was systemically researched to understand the structure-property relationships deeply to accumulate the increase of device performance rationally and accelerate the commercialization of OLEDs. The high thermal (T_d, 394 °C) and morphological stabilities of SFX-PzO₂ were obtained due to its rigid spiroconfigured structure and 3D steric hindrance effect. The twisted non-conjugation connection between spiro [fluoren-9,9′-xanthen] and phenothiazine dioxide ensures the compound possesses high triplet energy level (2.87 eV), which is vital to achieve high performance devices. A SFX-PzO₂ hosted blue TADF device was achieved as a host with the maximum external quantum efficiency (EQE) and lowest driving voltage of 13.9% and 6.5 V at a luminance of 1000 cd m⁻², respectively, for phenothiazine dioxide derivative hosted device.