New strategy for developing deep blue TADF materials with narrow emission and CIE_y < 0.06 employing host materials as donors

Achieving deep blue thermally activated delayed fluorescent (TADF) materials with narrow emission still remains a challenge. Herein, two deep blue TADF emitters DCBTRZ and PPCTRZ were designed and synthesized by directly using host materials, 1,4-di(carbazol-9-yl)benzene (DCB) and 2-[4-(9H-carbazol-9-yl)phenyl]-1-phenyl-1H-phenanthro[9,10-d]imidazole (PPC) as donors, and 2,4,6-triphenyl-1,3,5-triazine (TRZ) as an acceptor. The two emitters have typical TADF properties. Both of them can emit deep blue fluorescence with a very narrow full-width at half-maximum (FWHM) of 42 nm in toluene. The photoluminescence quantum yields (PLQYs) of DCBTRZ and PPCTRZ are 39.6% and 38.2% in doped films, respectively. Devices based on DCBTRZ and PPCTRZ achieve deep blue emission (440 and 442 nm) with maximum external quantum efficiencies (EQE_max) of 6.68% and 6.55%, respectively. Meanwhile, they exhibit very high color purity. The CIE_y and FWHM of devices employing DCBTRZ and PPCTRZ are 0.059/0.063 and 56/54 nm, respectively, meeting the standard of NTSC for deep-blue emitters, which indicates excellent application prospects in displays. The results suggest that this strategy for developing deep blue TADF materials with narrow emission and CIE_y < 0.06 directly employing host materials as donors is feasible and effective.