The planar conformer is dominant in the crystalline phase, while in solution the twisted conformer is largely responsible for the observed photophysics, giving rise to TADF. The PXZ-PPO-based device, with EQEmax of 14.1% at λEL of 528 nm, is slightly inferior to the OLED based on PXZ-BOO, which has an EQEmax of 19.4% at λEL of 528 nm.