Highly efficient blue TADF emitters incorporating bulky acridine moieties and their application in solution-processed OLEDs

Two bulky acridine moieties, 9,9-diphenyl-9,10-dihydroacridine (DPAc) and 10H-spim [acridine-9,9'-fluorene] (SpiroAc), were selected as electron donors. Compared with commonly used 9,9-dimethyl-9,10-dihydroacridine (DMAc), phenyl modified acridines exhibited low-lying highest occupied molecular orbital (HOMO) levels and relatively weak electron-donating abilities, which make them potential units to create blue TADF emitter. DPAc and SpiroAc were connected with a triarylboron group and constructed centrosymmetric 3D-A architectures, namely 3DPAc-TB and 3SpiroAc-TB, respectively. Density functional theory calculations showed that both molecules exhibited large dihedral angles between the triarylboron unit and acridine planes. The well-separated frontier molecular orbitals contributed to small energy gaps between S-1 and T-1 states of the designed molecules (0.12 and 0.07 eV, respectively). Both molecules exhibited distinct thermally activated delayed fluorescence (TADF) character. The bulky acridine donors endowed both molecules with rigid structures and realized high photoluminescent quantum yields (71.6% and 84.3%, respectively). Solution-processed organic light-emitting diodes (OLEDs) utilizing 3DPAc-TB and 3SpiroAc-TB as emitters exhibited blue emissions with emission peaks of 472 nm and 490 nm, respectively. The maximum external quantum efficiencies of 3DPAc-TB and 3SpiroAc-TB based devices were 12.8% and 17.3%, respectively.

Automated summary

Two bulky acridine moieties, DPAc and SpiroAc, were chosen as electron donors to create blue TADF emitters with high photoluminescent quantum yields in OLEDs. The molecules exhibited distinct TADF character and high external quantum efficiencies, demonstrating their potential for optoelectronic applications.