New bipolar derivatives with diphenylsulfone or dibenzophenone as TADF based emitters for OLEDs

With an aim to provide a balanced charge flux for enhanced PhOLED device efficiency, two novel bipolar host materials, 3-CBZ-QZ and 9-CBZ-QZ, incorporating carbazole and quinazolinone as the electron donor and acceptor, respectively, have been synthesized, characterized, and used as efficient host materials for phosphorescent devices. Furthermore, their photophysical, thermal, and electrochemical properties have been investigated to shed the importance on the structure−performance relationship. 3-CBZ-QZ and 9-CBZ-QZ have high triplet energies of 3.09 and 2.54 eV, respectively, which make them suitable host materials for green emitters in the emissive layer (EML). DFT studies reveal high charge mobilities for both synthesized molecules based on electron and hole reorganization energy calculations. This balanced charge-carrying capacity prompted us to fabricate simple three-layer devices with a single hole and electron transport layer across the EML. The 3-CBZ-QZ-based device resulted in a superior electroluminescent (EL) performance with a turn-on voltage of 2.6 V, a maximum luminance of 77973 cd/m 2 , a maximum power efficiency of 71.0 Im/W, and an EQE of 18.1%. Although devices with the 9-CBZ-QZ host demonstrated a lower EQE of 16.0%, it showed a higher luminance value of 91111 cd/m 2 than 3-CBZ-QZ with a significantly lower efficiency roll-off at a higher practical luminance of 100 cd/m 2 . The EL characteristics significantly varied with the positional changes in the donor−acceptor linkage. Moreover, these recorded performances demonstrate the promising advantage of the carbazole−quinoxaline-based compounds in developing host materials for realizing efficient PhOLEDs.

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“Molecular Designs Featuring Cyanobenzene-Decorated Phenazine Acceptor Units for the Highly Efficient Deep-Red Thermally Activated Delayed Fluorescent Emitters”

Madagyal,

Paul,

Yang

et al. 2024

ACS Appl. Opt. Mater.

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The design and development of long-wavelength deep-red emitters have gained significant attention due to their potential prospective applications in optical communication, nightvision devices, and sensors. However, due to the intrinsic limitations of the energy gap law, creating high-performing deepred emitters is still found to be difficult. Herein, based on the auxiliary cyanobenzene core attached to the phenazine acceptor unit, we have reported two types of orange-red to deep-red emitting thermally activated delayed fluorescence (TADF) emitters, 4,4′-(3,6-bis(9,9-dimethylacridin-10(9H)-yl)dibenzo[a,c]phenazine-11,12-diyl)dibenzonitrile (Ac-PhCNDBPZ) and 4,4′-(3,6-di(10H-phenoxazin-10-yl)dibenzo[a,c]phenazine-11,12-diyl)dibenzonitrile (PXZ-PhCNDBPZ). A direct attachment of donor units to the phenazine acceptor unit was preferred for steric repulsion between the donor and acceptor units. Hence, more twisted molecular structures are necessary for a small singlet−triplet energy gap (ΔE ST ). Terminal cyanobenzene units helped to further shift the emission wavelength toward the long wavelength region and to minimize the intermolecular interaction to suppress the aggregation-caused emission quenching. Both these emitters exhibited a very small singlet−triplet energy gap (0.13 and 0.06 eV) and short DF lifetime (τ d ) values (2.62 and 1.63 μs). Vacuum-deposited organic light-emitting diodes using Ac-PhCNDBPZ and PXZ-PhCNDBPZ as emitters displayed orange-red and deep-red electroluminescence having maximum external quantum efficiencies of 10.5% and 9.9%, respectively. This work shows that high-efficiency deep-red TADF materials are efficiently produced by combining a cyano substituent with a strong and rigid acceptor.

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New bipolar derivatives with diphenylsulfone or dibenzophenone as TADF based emitters for OLEDs

Cited by 4 publications

References 39 publications

Quinoxaline-based host materials for organic light-emitting diodes

Quinoxaline-based host materials for organic light-emitting diodes

Enhanced Efficiency in Green PhOLEDs Using a Simplified Three-Layer Architecture with Bipolar Carbazole–Quinazolinone Hosts

“Molecular Designs Featuring Cyanobenzene-Decorated Phenazine Acceptor Units for the Highly Efficient Deep-Red Thermally Activated Delayed Fluorescent Emitters”

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