Blue Aggregation‐Induced Emission Luminogens: High External Quantum Efficiencies Up to 3.99% in LED Device, and Restriction of the Conjugation Length through Rational Molecular Design

Abstract

7645wileyonlinelibrary.com with external quantum effi ciencies up to 9.9%, nearly doubling the theoretical upper limit (5%) for fl uorescent devices. [ 5 ] This exciting result re-attracted many interests on the pure organic fl uorophors. [ 6,7 ] On the other hand, from 2001, pioneered by Tang et al., the research of organic fl uorophors with the characteristic of aggregation-induced emission (AIE) has become a hot topic. [8][9][10][11] And according to Tang's concept for lightemitting materials, the designed AIEgens demonstrated totally different emissive behavior from conventional fl uorophores with the notorious aggregation-caused quenching (ACQ) effect in the solid state: a series of propeller-like molecules were turned from faint fl uorophores in solution to strong emitters in the aggregation state, derived from the restricted rotation of some aromatic rings. Especially, one typical AIE molecule, 1-methyl-1,2,3,4,5-pentaphenylsilole, demonstrated very high effi ciency of 8% in its OLED device. [ 8,9 ] The emission color was not blue, but green, possibly due to the relatively long conjugation length of this molecule. [ 10 ] Actually, there were few reports concerning the blue AIE fl uorophors, once again showing the diffi culty to achieve good blue organic light-emitting materials.Fortunately, in the past several years, by utilizing different linkage modes and increasing the twisting degree of the molecules in the presence of additional groups, we have successfully developed facile approaches to tune the balance of the molecular rotation and conjugation, and construct blue AIE luminogens. [ 11 ] The OLED devices clearly demonstrated that their intrinsic band gaps have been effi ciently restricted for blue or deep-blue emissions, and the maximum current efficiency is up to 3.74 cd A −1 . Is there any more room to further improve the effi ciency? Considering the different function of the two design strategies, we are wondering how about the combination of these two methods, perhaps, the effect of "one plus one larger than two" could be realized. Thus, we designed and synthesized a series of AIE molecules, TPA-3 m TPE, TPA-3MethylTPE, MethylTPA-3 p TPE, MethylTPA-3 m TPE and MethylTPA-3MethylTPE ( Chart 1 ), by utilizing triphenylamine (TPA) or methyl-substituted TPA as core and tetraphenylethene (TPE) derivatives in peripheries. Indeed, the combination made the conjugation of the fi ve molecules fi nely tuned Great efforts have been devoted to seek novel approaches for constructing blue fl uorescent materials, which is one of the most important prerequisites for the commercialization of OLEDs. In recent years, various outstanding luminogens with aggregation-induced emission characteristic exhibit promising applications as emitters, but blue AIE fl uorophores with excellent EL performance are still very scarce. Here, fi ve hole-dominated blue AIE molecules are demonstrated by adopting construction approaches of changing linkage modes and increasing intramolecular torsion together, with the aim to restrict c...

Cost-Effective Force Field Tailored for Solid-Phase Simulations of OLED Materials

“…The investigation is particularly timely because of the rise, besides transition metal-based phosphorescent emitters, of new all-organic ones with thermally activated 12,13,[31][32][33][34][35] and aggregation induced fluorescence [14][15][16]36 playing a major role, that are going to consent the realization of fully organic OLEDs, and represents the ideal prosecution of our previous study on the accurate theoretical calculation of singlet-triplet energy gaps for this class of materials. 34 …”

“…1 as donors and acceptors for organic solar cells, 2,3 metal-free dyes 4,5 or hole transporters 6 in Graetzel solar cells, host semiconducting [7][8][9][10][11][12] and emitting materials in organic light-emitting diodes (OLEDs), 9,[13][14][15][16][17] to name the most important ones. In particular all the emissive, hole and electron conducting (blocking) layers in small molecule and polymer OLEDs are often composed by nitrogen-rich units featuring a sp 2 or sp 3 -hybridized nitrogen (e.g.…”

Carbon Dots with Dual‐Emissive, Robust, and Aggregation‐Induced Room‐Temperature Phosphorescence Characteristics

“…Contrary to the traditional fluorophores, materials with AIE properties are known to exhibit intense fluorescence (FL) only at solid or aggregated state but are not emissive in a dilute solution . Such a unique feature makes the AIE‐active materials to be particularly useful in the fields of biomedicine (for example, achieving high‐contrast bioimaging and targeted therapy) and optoelectronics (for example, avoiding aggregation‐caused quenching (ACQ) effect of the emitting layer in light‐emitting diodes (LEDs)) . Except for the AIE of fluorescence, materials with AIE of phosphorescence properties had also been designed and prepared recently, which presented even more advantages due to their long emission lifetimes and possibly to fully utilize their excited state energy .…”

Manipulating the Molecular Backbone to Achieve Highly Emissive Sky‐Blue AIEgens and Their Applications in Nondoped Organic Light‐Emitting Diodes

“…Moreover, the unstable phase separations for these reported guest-host systems upon heating could also result the performance degradation. [19] Inspired by this work, 2-CzTPE and 2,7-CzTPE with promising AIE features were synthesized here to balance the trade-off between twisted molecular conformation and enlarged molecular conjugation, and their relationships between molecular structures and luminescent performance were also investigated in details. Encouragingly, using highly emissive AIEgens as emitters in OLEDs provided the pragmatic platform to solve these problems and then afforded the efficient nondoped OLEDs.…”