Another strong electron-withdrawing group, CN, was used in lieu of the trifluoromethyl groups in a series of emitters reported by Hong et al (Figure ). Compared to TRZCz-CF3, CzCNTRZ (λPL: 458 nm; FPL: 46%; τd: 47.9 µs; ΔEST: 0.21 eV; 10 wt% in DPEPO) shows a similar emission maximum and improved FPL but at the cost of a larger ΔEST of 0.21 eV. The similar emission was attributed to the identical electron-withdrawing ability of the two electronwithdrawing groups; however, the larger ΔEST is indicative of a smaller steric bulk from the CN substituent. Thanks to the higher FPL, the EQEmax of the CzCNTRZ-based device reached 13.9%. Similar to the PL spectrum, the CzCNTRZ device showed blue (lEL = 461 nm) emission with CIE coordinates of (0.15, 0.16), which resembles the emission profile of the TRZCz-CF3 device (lEL = 464 nm).