Organic Chemistry

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

Authors

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

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Content

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Supplementary material

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TADF/RTP OLED organic emitters based on concaved N-PAHs with tunable intrinsic D-A electronic structure
We report on developing the fully conjugated, curved N-PAHs containing phenazine terminus with the D-A electronic structures, which are herein studied as functional optoelectronic material. We evidence the influence of curvature on minimizing HOMO-LUMO overlap, which was severely reflected in small ΔEST values, indispensable to enhance the RISC rate constant. Within this approach, we evaluate the utility of the concaved system as TADF/RTP emitters which has not been explored so far in the context of non-planar N-PAHs. By variable accepting strength of phenazines employed, the photolumines-cence quantum yields (ΦPL) were tuned, ranging from the lowest 9% up to the highest 86% with dinitrile terminus. As a proof of concept, solid-state OLED devices were constructed, exhibiting yellow to orange emission with the best maximum external EL quantum efficiency (EQE) of 12% for acceptor built up on 3-(trifluoromethyl)phenyl decorated phenazine that is demonstrated for the first time for curved D-A embedded N-PAHs