Although bowl‐shaped N‐pyrrolic polycyclic aromatic hydrocarbons (PAHs) can achieve excellent electron‐donating ability, their application for optoelectronics is hampered by typically low photoluminescence quantum yields (PLQYs). To address this issue, we report the synthesis and characterization of a series of curved and fully conjugated nitrogen‐doped PAHs. Through structural modifications to the electron‐accepting moiety, we are able to switch the mechanism of luminescence between thermally activated delayed fluorescence (TADF) and room‐temperature phosphorescence (RTP), and to tune the overall PLQY in the range from 9 % to 86 %. As a proof of concept, we constructed solid‐state organic light‐emitting diode (OLED) devices, which has not been explored to date in the context of concave N‐doped systems being TADF/RTP emitters. The best‐performing dye, possessing a peripheral trifluoromethyl group adjacent to the phenazine acceptor, exhibits yellow to orange emission with a maximum external quantum efficiency (EQE) of 12 %, which is the highest EQE in a curved D‐A embedded N‐PAH to date.

No abstract

Owing to their strong carbazole chromophore and fluorophore, as well as to their powerful and convergent hydrogen bond donors, 1,8-diaminocarbazoles are amongst the most attractive and synthetically versatile building blocks for the construction of anion receptors, sensors, and transporters. Aiming to develop carbazole-based colorimetric anion sensors, herein we describe the synthesis of 1,8-diaminocarbazoles substituted with strongly electron-withdrawing substituents, i.e., 3,6-dicyano and 3,6-dinitro. Both of these precursors were subsequently converted into model diamide receptors. Anion binding studies revealed that the new receptors exhibited significantly enhanced anion affinities, but also significantly increased acidities. We also found that rear substitution of 1,8-diamidocarbazole with two nitro groups shifted its absorption spectrum into the visible region and converted the receptor into a colorimetric anion sensor. The new sensor displayed vivid color and fluorescence changes upon addition of basic anions in wet dimethyl sulfoxide, but it was poorly selective; because of its enhanced acidity, the dominant receptor-anion interaction for most anions was proton transfer and, accordingly, similar changes in color were observed for all basic anions. The highly acidic and strongly binding receptors developed in this study may be applicable in organocatalysis or in pH-switchable anion transport through lipophilic membranes.

Despite promising optoelectronic features of Ndoped polycyclic aromatic hydrocarbons (PAHs), their use as functional materials remains underdeveloped due to their limited post-functionalization. Facing this challenge, a novel design of Ndoped PAHs with D−A−D electronic structure for thermally activated delayed fluorescence (TADF) emitters was performed. Implementing a set of auxiliary donors at the meta position of the protruding phenyl ring of quinoxaline triggers an increase in the charge-transfer property simultaneously decreasing the delayed fluorescence lifetime. This, in turn, contributes to a narrow (0.04− 0.28 eV) singlet−triplet exchange energy split (ΔE ST ) and promotes a reverse intersystem crossing transition that is pivotal for an efficient TADF process. Boosting the electron-donating ability of our N-PAH scaffold leads to excellent photoluminescence quantum yield that was found in a solid-state matrix up to 96% (for phenoxazine-substituted derivatives, under air) with yellow or orange-red emission, depending on the specific compound. Organic light-emitting diodes (OLEDs) utilizing six, (D−A)−D, N-PAH emitters demonstrate a significant throughput with a maximum external quantum efficiency of 21.9% which is accompanied by remarkable luminance values which were found for all investigated devices in the range of 20,000−30,100 cd/m 2 which is the highest reported to date for N-doped PAHs investigated in the OLED domain.

We report the synthesis and characterization of a series of donor-acceptor TADF emitters with a new architecture, where the donor moiety and the dibenzazepine-based acceptor moiety are separated by a...

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

Although bowl‐shaped N‐pyrrolic polycyclic aromatic hydrocarbons (PAHs) can achieve excellent electron‐donating ability, their application for optoelectronics is hampered by typically low photoluminescence quantum yields (PLQYs). To address this issue, we report the synthesis and characterization of a series of curved and fully conjugated nitrogen‐doped PAHs. Through structural modifications to the electron‐accepting moiety, we are able to switch the mechanism of luminescence between thermally activated delayed fluorescence (TADF) and room‐temperature phosphorescence (RTP), and to tune the overall PLQY in the range from 9 % to 86 %. As a proof of concept, we constructed solid‐state organic light‐emitting diode (OLED) devices, which has not been explored to date in the context of concave N‐doped systems being TADF/RTP emitters. The best‐performing dye, possessing a peripheral trifluoromethyl group adjacent to the phenazine acceptor, exhibits yellow to orange emission with a maximum external quantum efficiency (EQE) of 12 %, which is the highest EQE in a curved D‐A embedded N‐PAH to date.

Polycyclic aromatic hydrocarbons (PAHs) with centrally positioned nitrogen dopants possess a unique curved structure and strong electron-donating features. However, the lack of tools to synthetically affect their bandgap engineering and charge-transfer (CT) characteristic is detrimental to their future optoelectronics use because of usually low PLQY effi-ciency. Facing this challenge, we report on developing the first 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, in-dispensable 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 photoluminescence 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, exhibit-ing 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.