Cz-PS has an electron deficient diphenylsulfonyl core with two electron donating di-tert-butyl substituted carbazolyl peripheral end groups. The bulky tert-butyl substituents can not only stabilize the molecule by blocking the electron rich 3,6-position to prevent the formation of dimers but also, they can effectively prevent the formation of the excimers.
Bis[4-(3,6-di-tert-butylcarbazole)phenyl]sulfone demonstrated deep-blue emission and the OLED with the dopant achieved a high EQE of 9.9% by using DPEPO as the host. Meanwhile, the OLED device suffered from a sharp efficiency roll-off at high current density, primarily caused by the relatively large energy gap between the S1 and T1 states (ΔEST = 0.32 eV).