High‐Efficiency Solution‐Processable OLEDs by Employing Thermally Activated Delayed Fluorescence Emitters with Multiple Conversion Channels of Triplet Excitons

Abstract

The state-of-the-art luminescent materials are gained widely by utilizing thermally activated delayed fluorescence (TADF) mechanism. However, the feasible molecular designing strategy of fully exploiting triplet excitons to enhance TADF properties is still in demand. Herein, TADF emitters with multiple conversion channels of triplet excitons are designed by concisely halogenating the electron acceptors containing carbonyl moiety. Compared with the chlorinated and brominated analogues, the fluorinated emitter exhibits distinguishing molecular stacking structures, participating in the formation of trimers through integrating C-H•••F and C═O•••H hydrogen bonds together. It is also demonstrated that the multiple channels can be involved synergistically to accelerate the spin-flip of triplet excitons, and to take charge of the relatively superior reverse intersystem crossing constant rate of 6.20 × 10 5 s -1 , and thus excellent photoluminescence quantum yields over 90% can easily be achieved. Then the solution-processable organic light emitting diode based on fluorinated emitter can achieve a record-high external quantum efficiency value of 27.13% and relatively low efficiency roll-off with remaining 24.74% at 1000 cd m −2 . This result manifests the significance of enhancing photophysical properties through constructing multiple conversion channels of triplets excitons for high-efficiency TADF emitters and provides a guideline for the future study.

Constructing high-efficiency orange-red thermally activated delayed fluorescence emitters by three-dimension molecular engineering

“…With the rapid progress of materials chemistry, many kinds of solution-processable TADF emitters are successfully prepared already, especially for blue-green emitters 11 – 15 . For instance, the maximum external quantum efficiency (EQE max ) of up to 27.13% for blue-green solution-processed OLEDs has been obtained 16 . However, the performance of solution-processable orange-red TADF emitters with a wavelength ranging from 560 to 630 nm are significantly unsatisfactory comparing with the blue-green ones.…”

Tuning excited state energy levels by achieving coordination-induced thermally activated delayed fluorescence

“…Coupled with T 1 and T 2 , we can infer that multiple conversion channels are favorable for the RISC process. 26 Hence, a high RISC rate is achieved as aforementioned.…”

Thermally activated delayed fluorescence with dual-emission and pressure-induced bidirectional shifting: cooperative effects of intramolecular and intermolecular energy transfer

“…26 The introduction of fluorine atom is used to enhance intramolecular and intermolecular electron communications. [27][28][29] 9,9-dimethyl-9,10-dihydroacridine (DMAC) and 10H-phenoxazin (PXZ) are commonly employed as donor units in TADF systems due to their rigid structure, controllable electrondonating ability and easy implementation, [30][31][32][33][34] but they are used in UV TADF materials for the first time.…”