Efficient Aggregation-Induced Delayed Fluorescence Luminogens for Solution-Processed OLEDs With Small Efficiency Roll-Off

Abstract

Purely organic small molecules with thermally-activated delayed fluorescence have a high potential for application in organic light-emitting diodes (OLEDs), but overcoming severe efficiency roll-off at high voltages still remains challenging. In this work, we design and synthesize two new emitters consisting of electron-withdrawing benzoyl and electron-donating phenoxazine and 9,9-dihexylfluorene. Their electronic structures, thermal stability, electrochemical behaviors, photoluminescence property, and electroluminescence performance are thoroughly investigated. These new emitters show weak fluorescence in dilute solution, but they can emit strongly with prominent delayed fluorescence in the aggregated state, indicating the aggregation-induced delayed fluorescence (AIDF) character. The solution-processed OLEDs based on the two emitters show high external quantum efficiency of 14.69%, and the vacuum-deposited OLEDs can also provide comparable external quantum efficiency of 14.86%. Significantly, roll-offs of the external quantum efficiencies are very small (down to 0.2% at 1,000 cd m −2) for these devices, demonstrating the evidently advanced efficiency stability. These results prove that the purely organic emitters with AIDF properties can be promising to fabricate high-performance solution-processed OLEDs.

Aggregation induced delayed green fluorescence from assembly of gold nanoclusters: an advanced probe for “background free” pyrophosphate recognition

“…However, upon formation of rigid assemblies such relaxation processes are highly restricted thereby prolonging the life time of the excited states of the clusters and making them available for ISC and reverse ISC. 36…”

Thermally Activated Delayed Fluorescence: Beyond the Single Molecule

“…While there has been vast development of new TADF emitters and our understanding of the fundamental processes of rISC and the spin states has developed, it is now time to look towards understanding these processes in non-ideal situations using the techniques and framework discussed above. This framework will facilitate the development and understanding of functional materials that are sensitive to mechanical and thermal energy while opening up pathways to AIE-based, non-doped OLEDs (Furue et al, 2016;Liu et al, 2018a;Cai et al, 2020;Yang et al, 2020). It will also help unify the study of intramolecular TADF emitters with the studies of polymorphism (Chung and Diao, 2016;Bernstein, 2020;Levesque et al, 2020) exciplexes (Kim et al, 2016;Sarma and Wong, 2018;Tang et al, 2020) and hostguest interactions (Matsunaga and Yang, 2015;Feng et al, 2017;Ono et al, 2018).…”

Supramolecular self-assembly mediated aggregation-induced emission of fluorene-derived cyanostilbenes: multifunctional probes for live cell-imaging

“…8 c To better understand this phenomenon, several synthetic modifications and theoretical calculations were undertaken; the results revealed that the restriction of intramolecular motions, which led to rotation, vibration, and stretching, played a key role in the AIE phenomenon. Several synthetic modifications on organic fluorophores have been developed for AIE materials including siloles, 9 triphenylamine (TPA), 10 cyanostilbenes, 11 tetraphenylethenes, 12 a – d naphthalenediimide 12 e , f and anthracene 13 derivatives, diphenyldibenzofulvenes, 14 BODIPYs, 15 diketopyrrolopyrrole, 16 and fluorene derivatives, 17,18 The enhanced emission of all the AIEgens in their aggregate and solid forms is due to the nonplanar aromatic backbone that restricts the formation of π–π stacking. 5 On the other hand, supramolecular self-assembly of π-conjugated organic fluorescent molecules exhibits the AIE property in the aggregate state.…”