A Terminal Carbazole Fused Ladder-Type B,N-Doped Multiresonant Thermally Activated Delayed Fluorescence Emitter: A Strategy for Deep-Blue Emission

Abstract

Attaining precise control of emission within the blue spectral region remains inherently challenging for ladder-type π-extended multiresonant thermally activated delayed fluorescent (MR-TADF) compounds, despite their many advantageous design features. Here, we aim to address the undesired redshifting of the emission in ladder-type MR-TADF compounds by incorporating terminal fused carbazoles. We report two MR-TADF compounds, B2N3 and B3N3, the latter of which is a p- and n-doped heptacene polycyclic aromatic π-hydrocarbon (PAH), both of which contain fused carbazoles at both ends of the molecule. Relative to the previously reported MR-TADF compound α-3BNMes, the emission of B3N3 is blueshifted and narrower, emitting at λ_PL of 427 nm and having a full width at half maximum (FWHM) of 25 nm in toluene. In contrast, B2N3, which is more conformationally flexible, emits at λ_PL of 441 nm and has a FWHM of 32 nm in toluene. Sensitized organic light-emitting diodes (OLEDs) using B2N3 and B3N3 as terminal emitters showed EQE_max of 12.8% and 10.7% emitting with CIE coordinates of (0.15, 0.10) and (0.16, 0.09), respectively.