TADF/RTP OLED organic emitters based on concaved N-PAHs with tunable intrinsic D-A electronic structure

Abstract

The introduction of pyrrolic nitrogen dopants into the central sites of polycyclic aromatic hydrocarbons (PAHs) often gives rise to characteristic bowl-shaped structures due to the simultaneous introduction of 5- and/or 7-membered cycles. Although the incorporation of these heteroatoms achieves excellent electron-donating ability, the application of this strat-egy for the design of optoelectronics is hampered by typically low photoluminescence quantum yields (PLQYs). In order to address this issue, in the present study we report the synthesis and characterization of the first curved and fully conju-gated nitrogen-doped PAHs in which an electronically diverse phenazine terminus serves as the electron-accepting moie-ty. We show that the curvature of the molecular skeleton increases the spatial separation between the HOMO and the LUMO, leading to low singlet-triplet gaps, which are essential for high reverse intersystem crossing (RISC) rates. Moreo-ver, we evaluate the utility of the concave N-doped systems as TADF/RTP emitters, which has not been explored so far in the context of non-planar N-PAHs. By varying the electron-accepting ability of the phenazine terminus, we are able to tune the PLQY of the given compounds in a range from 9% to 86% (for a dinitrile substituted derivative). As a proof of con-cept, we constructed solid-state OLED devices exhibiting yellow to orange emission. The best-performing compound, built from a 3-(trifluoromethyl)phenyl decorated phenazine acceptor, shows a maximum external EL quantum efficiency (EQE) of 12%, which is the highest EQE in an curved D-A embedded N-PAH to date