Color‐Tunable Boron‐Based Emitters Exhibiting Aggregation‐Induced Emission and Thermally Activated Delayed Fluorescence for Efficient Solution‐Processable Nondoped Deep‐Blue to Sky‐Blue OLEDs

Abstract

Three new color‐tunable (deep‐blue to sky‐blue) and solution‐processable emitters—9′‐(2,12‐di‐tert‐butyl‐5,9‐dioxa‐13b‐boranaphtho[3,2,1‐de]anthracen‐7‐yl)‐9′H‐9,3′:6′,9″‐tercarbazole (TB‐3Cz), 9′‐(2,12‐di‐tert‐butyl‐5,9‐dioxa‐13b‐boranaphtho[3,2,1‐de]anthracen‐7‐yl)‐9,9″‐diphenyl‐9H,9′H,9″H‐3,3′:6′,3″‐tercarbazole (TB‐P3Cz), and 9‐(2,12‐di‐tert‐butyl‐5,9‐dioxa‐13b‐boranaphtho[3,2,1‐de]anthracen‐7‐yl)‐N3,N3,N6,N6‐tetraphenyl‐9H‐carbazole‐3,6‐diamine (TB‐DACz)—are demonstrated, which are cleverly designed and synthesized by appending a boron‐fused entity as an electron acceptor to different electron‐rich entities containing carbazole derivatives as donors. The thermal, photophysical, electrochemical, and electroluminescent characteristics of all the new materials are extensively investigated. Comprehensive photophysical investigations reveal that these emitters exhibit not only thermally activated delayed fluorescence (TADF) but also aggregation‐induced emission (AIE) properties. Consequently, solution‐processable organic light‐emitting diodes (OLEDs) fabricated using these new materials as nondoped emitters in the emissive layer exhibit a maximum external quantum efficiency (EQE) and Commission Internationale de l'Éclairage (CIE) color coordinates of 9.90% and (0.17, 0.07), respectively, for TB‐3Cz; 6.13% and (0.15, 0.08), respectively, for TB‐P3Cz; and 6.04% and (0.18, 0.40), respectively, for TB‐DACz. As far as it is known, the performance and ultrahigh color purity satisfying the deep‐blue CIE coordinates of the National Television System Committee (NTSC) for TB‐3Cz and TB‐P3Cz are the highest reported thus far for nondoped solution‐processable TADF emitters, indicating the great potential of these materials as deep‐blue luminogens in OLED applications.

A TADF Emitter Featuring Linearly Arranged Spiro‐Donor and Spiro‐Acceptor Groups: Efficient Nondoped and Doped Deep‐Blue OLEDs with CIEy<0.1

“…[5] Due to the lack of proper deep-blue emitters,t he nondoped deep-blue OLEDs with CIE y < 0.1 still suffer from low efficiencies.T othe best of our knowledge,t he most efficient one was reported to have the EQE lower than 10 %. [4,6] In recent years,thermally-activated delayed fluorescence (TADF) emitters that can harvest triplet excitons for emission has greatly promoted the development of deep-blue OLEDs. [7] Them ost commonly used TADF-type deep-blue emitters are those constructed by electron donor (D) and acceptor (A) groups.A mong various donors adopted, spiro[acridine-9,9'-fluorene] (sAC) and its derivatives with alkyl substituents,e xtended spiro-structure,o rm ore hetero atoms (e.g.,Siand O) are of special interest.…”

“…As for deep-blue OLEDs,t he "nondoped" feature also avoids the tough matching of host materials. [4] Despite these virtues,t he realization of highly efficient nondoped deep-blue OLEDs with CIE y < 0.1 is even more challenging because it sets an additional request to deep-blue emitters,w hich is the ability to overcome the tiresome concentration quenching. [5] Due to the lack of proper deep-blue emitters,t he nondoped deep-blue OLEDs with CIE y < 0.1 still suffer from low efficiencies.T othe best of our knowledge,t he most efficient one was reported to have the EQE lower than 10 %.…”

A multifunctional luminescent material based on quinoxaline and triphenylamine groups: polymorphism, mechanochromic luminescence, and applications in high-efficiency fluorescent OLEDs

“…Organic emitting materials have exhibited huge potential due to their advantages, such as low cost, long lifetimes, and flexibility. 1–5 Generally, a single luminescent molecule only possesses one emission color based on Kasha's rule. 6 To achieve various emission colors and photophysical properties, sophisticated synthesis and purification processes have to be used.…”

Solution-processable orange-red thermally activated delayed fluorescence emitters with 3,6-disubstituted carbazole for highly efficient OLEDs with low efficiency roll-off

“…The relatively high decay rate constants for the intersystem crossing (ISC) and RISC processes of the two emitters could accelerate these processes and facilitate radiative transitions. 48,49 These results suggest that the two novel compounds are efficient TADF emitters and encouraged us to investigate their device performance.…”