Triazine-Acceptor-Based Green Thermally Activated Delayed Fluorescence Materials for Organic Light-Emitting Diodes

Abstract

High-efficiency thermally activated delayed fluorescence (TADF) is leading the third-generation technology of organic light-emitting diodes (OLEDs). TADF emitters are designed and synthesized using inexpensive organic donor and acceptor derivatives. TADF emitters are a potential candidate for next-generation display technology when compared with metal-complex-based phosphorescent dopants. Many studies are being conducted to enhance the external quantum efficiencies (EQEs) and photoluminescent quantum yield of green TADF devices. Blue TADF reached an EQE of over 35% with the support of suitable donor and acceptor moieties based on a suitable molecular design. The efficiencies of green TADF emitters can be improved when an appropriate molecular design is applied with an efficient device structure. The triazine acceptor has been identified as a worthy building block for green TADF emitters. Hence, we present here a review of triazine with various donor molecules and their device performances. This will help to design more suitable and efficient green TADF emitters for OLEDs.

Triangular boron carbon nitrides: an unexplored family of chromophores with unique properties for photocatalysis and optoelectronics

“…By the robust inversion of the energies of the S1 and T1 states, all BCNs are predestinated as chromophores for improved OLEDs. The so-called third generation OLEDs 27,29,69 rely on the mechanism of TADF 70 , exploiting thermally activated inverse intersystem crossing from long-lived triplet excitons to nearly degenerate singlet excitons. The essential requirement for TADF is a small (≈ kBT) positive ΔST, such that population of the long-lived triplet state can be thermally activated to the singlet state, from which fluorescence occurs.…”

“…Numerous molecules tailored for TADF were synthesized and tested as OLED emitters. [25][26][27][28][29]69 The existence of a large family of organic emitters with inverted S1/T1 states provides the basis for the development of a novel fourth generation of OLEDs. In materials with S1/T1 inversion, triplet excitons formed by recombination of electrons and holes readily convert to singlet excitons by ISC.…”

“…This implies the possible existence of a new (fourth) generation of emitters with higher luminescence efficiencies and spectral qualities than delivered by previous generations. [25][26][27][28][29] It is a disadvantage, however, that the transition dipole moment between the S1 state and the S0 state is very low in aza-phenalenes due to the non-overlapping character of HOMO and LUMO. In Cz and Hz, which exhibit D3h symmetry, this transition is additionally forbidden by symmetry.…”

Exciplex-Forming Systems of Physically Mixed and Covalently Bonded Benzoyl-1H-1,2,3-Triazole and Carbazole Moieties for Solution-Processed White OLEDs

“… 29 The effect of intramolecular charge transfer in excited states which is the result of D–A architecture has been widely used in the design of the compounds with numerous practically valuable photophysical properties including thermally activated delayed fluorescence (TADF), 30 , 31 room-temperature phosphorescence, 32 hybridized local and charge-transfer (HLCT), 33 and twisted intramolecular charge transfer. 34 In the design of TADF compounds, triazines, 35 cyanobenzenes, 36 benzophenones, 37 diphenylsulphones, 38 and other moieties 39 were used as acceptor units.…”

Fluorene–Triphenylamine-Based Bipolar Materials: Fluorescent Emitter and Host for Yellow Phosphorescent OLEDs

“…First-generation OLEDs are known as fluorescence OLEDs, and these were able to contribute only 25% of internal quantum efficiency while losing 75% in a non-radiative manner [7][8][9]. Later, phosphorescent OLEDs with metal and ligand complexes were identified as second-generation emitters in OLEDs.…”