Quinolinylmethanone-Based Thermally Activated Delayed Fluorescence Emitters and the Application in OLEDs: Effect of Intramolecular H-Bonding

Abstract

Three new quinoline TADF emitters, 2QPM-mDC, 2QPM-mDTC, and 4QPM-mDTC, were designed and synthesized and the emitters show ΔE ST as low as 0.07 eV and high PL quantum yield (PLQY) up to 98%. An electroluminescence device based on 2QPM-mDTC can reach high EQE over 24%. Compared with the reported TADF devices, the device shows narrow emission bandwidth and high color purity. The excellent device performance is likely ascribed to the molecular design of 2QPM-mDTC containing an intramolecular H-bonding in the molecule.

Revealing resonance effects and intramolecular dipole interactions in the positional isomers of benzonitrile-core thermally activated delayed fluorescence materials

“…In contrast, restrictions of quenching vibrational modes have been used to explain the superior performance of TADF materials exhibiting intramolecular hydrogen bonding. 55,56 In the delayed emission the electronic decoupling of donor and (weakest) acceptor in meta-2 results in a material with a low DE ST and fast rISC, but one without the ability to effectively undergo radiative decay from the singlet state and thus inferior PLQYs. These changes in CT and LE character during the meta-2 emission decay (and associated ISC and rISC rates) also then explain the difficulty in fitting the decay to a single exponential, while similar fitting is straightforward for the other two isomers.…”

Efficient Orange–Red Delayed Fluorescence Organic Light‐Emitting Diodes with External Quantum Efficiency over 26%

“…For the design of efficient TADF emitters, one key factor is to minimize the energy difference (ΔE ST ) between the lowest singlet (S 1 ) and triplet (T 1 ) states, and thus improve the up-conversion rate (k RISC ) from T 1 to S 1 and potentially increase the IQE of a device. [4,15,16] So far, the molecular design principles of TADF emitters generally have three species: twisted intramolecular charge transfer (TICT), through-space charge transfer (TSCT), and multi-resonance induced TADF (MR-TADF). [17] The most common molecular design strategy of TADF emitters is using a pre-twisted donor-acceptor (D-A) type structure with twisted intramolecular charge transfer (TICT) transition from the highest occupied molecule orbital (HOMO) to the lowest unoccupied molecule orbital (LUMO), which can significantly reduce the ΔE ST values.…”

“…Organic light-emitting diodes (OLEDs) have become a leading display technology due to their steadily improved efficiency and unique features such as fascinating flexibility, lightweight, no turn-on delay, superior color gamut, and wide viewing angle. [1][2][3][4][5][6] The key electroluminescent (EL) materials in OELDs are traditional fluorescent and phosphorescent materials. Fluorescent materials are inefficient with the maximum internal quantum efficiency (IQE) of only 25%, while phos-for orange-red/red TADF materials, since this PLQYs value can decrease with respect to the increase in emission wavelength in view of energy-gap law.…”

“…Organic light‐emitting diodes (OLEDs) have become a leading display technology due to their steadily improved efficiency and unique features such as fascinating flexibility, light‐weight, no turn‐on delay, superior color gamut, and wide viewing angle . The key electroluminescent (EL) materials in OELDs are traditional fluorescent and phosphorescent materials.…”

“…For the design of efficient TADF emitters, one key factor is to minimize the energy difference (Δ E ST ) between the lowest singlet (S 1 ) and triplet (T 1 ) states, and thus improve the up‐conversion rate ( k RISC ) from T 1 to S 1 and potentially increase the IQE of a device . So far, the molecular design principles of TADF emitters generally have three species: twisted intramolecular charge transfer (TICT), through‐space charge transfer (TSCT), and multi‐resonance induced TADF (MR‐TADF) .…”