Rajamalli et al., and Dos Santos et al., showed that the introduction of a heteroaromatic bridge in sulfone-based D-A TADF emitters can prevent structural relaxation, enhance FPL and improve the color purity due to the narrower emission, and demonstrated an improvement in the efficiency of the devices compared to that with the reference emitter pDTCz-DPS. The materials in the study of pDTCz-2DPyS, and pDTCz-3DPyS, both show good FPL of ca. 60%. The blue OLEDs, at lEL of 466 nm and 452 nm for the devices with pDTCz-2DPyS, and pDTCz-3Dpy, respectively, showed EQEmax ~12-13%, which are considerably improved over the parent device with pDTCz-DPS (EQEmax of 4.7%). Dos Santos et al., showed that the addition of second nitrogen atom within the bridging heterocycle in pDTCz-DPzS, and pDTCz-DPmS contributed to a further enhancement of the EQEmax to 18% and 14%, respectively, at lEL of 522 nm and 461 nm for the devices with pDTCz-DPzS, and pDTCz-DPmS, respectively. PXZ-BOO shows TADF, relevant devices having EQEmax of 19.4% at λEL of 528 nm. In THF solution, PXZ-PPO is present as a mixture of two conformers, a more planar structure with N-H interaction and a twisted structure, where hydrogen bonding is not present. The planar conformation emits in the deep blue at 420 nm but shows no TADF, while the twisted conformer shows green TADF (610 nm) but with a very short lifetime of 170 ns.