Triplet–Triplet Annihilation Enhanced Deep‐Blue Organic Light‐Emitting Diodes by Naphtho[1,2‐d]imidazole‐Isomer Derivatives with Spin–Orbit Coupling

Abstract

The utilization of triplet excitons is of great importance for organic light‐emitting diodes (OLEDs). Triplet–triplet annihilation (TTA) is one of the effective tactics to achieve high efficiency deep‐blue organic electroluminescence emitters by converting two triplet excitons into one singlet exciton. Whereas, in addition to the 25% electrogenerated singlet excitons, the proportion of radiative singlet excitons (RSE) produced by the TTA process is usually only 15%; thus the total radiative excitons are 40%. In this study, ≈35% of RSE is achieved by the TTA process (total 60%) with two deep‐blue emitters based on the isomeric naphthoimidazole (NI) unit and anthracene bridge. As a result, non‐doped OLEDs based on the two NI derivatives as emitting layers achieve maximum external quantum efficiencies of 10.9% and 11.2% with an identical deep‐blue emission peak of 452 nm, which are the best TTA OLEDs with a Commission Internationale de l'Eclairage chromaticity Y coordinate below 0.15. Theoretical and experimental results demonstrate that the TTA process can be improved owing to the efficient spin–orbit interactions, even though the energy levels of the triplet pairs are higher than the calculated second triplet excited states.

Realizing Stable Narrowband Emission Blue Fluorescent Organic Light-Emitting Diodes with Dual-Channel Triplet Exciton Harvesting Host

“…Because of the higher emission energy, the operational lifetime of blue OLEDs is much shorter than that of green and red ones. Various emitters and device structures have been developed to improve the efficiency and lifetime of blue OLEDs. − However, because of the low reverse intersystem crossing (RISC) rate of a multiresonance thermally activated delayed fluorescence (MR-TADF) emitter, the device operational lifetime of the narrow FWHM blue emitters is still unsatisfactory. Thus, realizing stable and narrow FWHM blue OLEDs is still a challenge and has important meaning.…”

Evaluating the Effect of Extended Conjugation and Regioisomerism on the Optoelectronic Properties and Device Efficiencies of Blue Light-Emitting Benzobisoxazoles

“…Thereafter, electrons can be transferred from the excited T 1 to the S 1 (when the E S1‑T1 < 0.2 eV), thereby increasing the S1 population from 25 to 100% and consequently overcoming the 5% external quantum efficiency (EQE) barrier of prompt fluorescence. TADF, however, is slower than direct fluorescence and depends on a material with efficient charge transfer (CT) abilities and a high potential for triplet exciton quenching due to the long lifetimes. , Deep-blue and blue-fluorescent organic emitters, such as those based on anthracene and pyrene derivatives, have also shown improved internal efficiencies beyond 25% by harnessing triplet–triplet annihilation (TTA) and their efficient spin–orbit coupling. − …”

Cyclocondensation of 2-(α-Diazoacyl)-2H-azirines with Amidines in Diazo Synthesis of Functionalized Naphtho[1,2-d]imidazoles

“…The selective cytotoxicity toward cancer cells and the fluorescence of naphtho­[1,2- d ]­imidazoles make possible the application of these compounds in antitumor theranostic systems . It was also found that naphtho­[1,2- d ]­imidazole derivatives are promising light-emitting materials for OLEDs. − Naphtho­[1,2- d ]­imidazoles are usually synthesized by condensation of carbonyl compounds with 1,2-diaminonaphthalene derivatives, ,,− often formed in situ. , Intramolecular condensation of 1-amido-2-amino/1-amino-2-amido-naphthalenes is also frequently used. ,,,, Another approach involves the cyclization of 1-aminonaphthalene derivatives containing an N-CRN moiety. − In all of the mentioned methods, the assembly of the tricyclic naphtho­[1,2- d ]­imidazole skeleton is completed by the formation of the imidazole ring (imidazole ring-forming strategy) (Scheme , (1a)). Only one compound of this series, 3-methyl-3 H -naphtho­[1,2- d ]­imidazole, was synthesized according to another scheme, involving the formation of the internal benzene ring at the last step (benzene ring-forming strategy) (Scheme , (1b)).…”