Solution-processable orange-red thermally activated delayed fluorescence hyper-structured molecular emitters containing diphenylamine substituted carbazole host units

Realizing solution-processable orange-red thermally activated delayed fluorescence (TADF) emitters is still challenging owing to the severe aggregation-caused quenching. In this study, N3,N3,N6,N6-tetraphenyl-9H-carbazole-3,6-diamine (DDPACz) with high triplet energy and good hole transport ability was chosen as host unit. And 1,8-naphthimide-9,9-dimethyl-9,10-dihydroacridine (NDMAC) was used as red TADF unit. Then, these two functional units were linked to the inactive calix[4]resorcinarene (CRA) core to construct a series of hyper-structured molecules (HSMs), CRA-NDMAC(x)-DDPACz(8-x) (x = 0, 1, 2, 4, 6, 7 or 8). 1H NMR, MALDI-TOF MS and FT-IR spectra indicated that HSMs were successfully synthesized. UV–Vis, PL and CV results demonstrated that these HSMs inherited the photophysical and electrochemical properties of functional units. Spin-coating CRA-NDMAC(x)-DDPACz(8-x) (x = 1, 2, 4, 6, 7 or 8) as light-emitting layer, all the non-doped solution processed organic light-emitting diodes (OLEDs) showed orange-red emission. Among them, CRA-NDMAC(1)-DDPACz(7)-based device showed the highest maximum external quantum efficiency (EQEmax) of 0.94% with the emission peak at 613 nm. Furthermore, bright orange emission at a central wavelength of 592 nm with EQEmax of 9.73% and luminance of 5428 cd/m2 was achieved in the doped OLED based on CRA-NDMAC(7)-DDPACz(1) using CBP as host. These results indicate that hyper-structured molecules could be a potential strategy for the construction of orange-red TADF emitters.