Ju Mei,†,‡,∥ Nelson L. C. Leung,†,‡,∥ Ryan T. K. Kwok,†,‡ Jacky W. Y. Lam,†,‡ and Ben Zhong Tang*,†,‡,§ †HKUST-Shenzhen Research Institute, Hi-Tech Park, Nanshan, Shenzhen 518057, China ‡Department of Chemistry, HKUST Jockey Club Institute for Advanced Study, Institute of Molecular Functional Materials, Division of Biomedical Engineering, State Key Laboratory of Molecular Neuroscience, Division of Life Science, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China Guangdong Innovative Research Team, SCUT-HKUST Joint Research Laboratory, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China

Aggregation-Induced Emission: Together We Shine, United We Soar!

"United we stand, divided we fall."--Aesop. Aggregation-induced emission (AIE) refers to a photophysical phenomenon shown by a group of luminogenic materials that are non-emissive when they are dissolved in good solvents as molecules but become highly luminescent when they are clustered in poor solvents or solid state as aggregates. In this Review we summarize the recent progresses made in the area of AIE research. We conduct mechanistic analyses of the AIE processes, unify the restriction of intramolecular motions (RIM) as the main cause for the AIE effects, and derive RIM-based molecular engineering strategies for the design of new AIE luminogens (AIEgens). Typical examples of the newly developed AIEgens and their high-tech applications as optoelectronic materials, chemical sensors and biomedical probes are presented and discussed.

Aggregation-Induced Emission: The Whole Is More Brilliant than the Parts

Although graphene films have a strong potential to replace indium tin oxide anodes in organic light-emitting diodes (OLEDs), to date, the luminous efficiency of OLEDs with graphene anodes has been limited by a lack of efficient methods to improve the low work function and reduce the sheet resistance of graphene films to the levels required for electrodes1,2,3,4. Here, we fabricate flexible OLEDs by modifying the graphene anode to have a high work function and low sheet resistance, and thus achieve extremely high luminous efficiencies (37.2 lm W–1 in fluorescent OLEDs, 102.7 lm W–1 in phosphorescent OLEDs), which are significantly higher than those of optimized devices with an indium tin oxide anode (24.1 lm W–1 in fluorescent OLEDs, 85.6 lm W–1 in phosphorescent OLEDs). We also fabricate flexible white OLED lighting devices using the graphene anode. These results demonstrate the great potential of graphene anodes for use in a wide variety of high-performance flexible organic optoelectronics. By replacing conventional indium tin oxide (ITO) anodes with high-work-function, low-sheet-resistance graphene anodes, researchers demonstrate flexible fluorescent organic LEDs with extremely high luminous efficiencies of 37.2 lm W–1 for fluorescent devices and 102.7 lm W–1 for phosphorescent devices. These values are significantly higher than those of optimized organic LEDs based on ITO anodes.

http://phome.postech.ac.kr/user/pnel/publication/95.%20T.-H.%20Han,%20Y.%20Lee,%20M.-R.%20Choi,%20S.-H.%20Woo,%20S.-H.%20Bae,%20B.%20H.%20Hong,%20J.-H.%20Ahn,%20T.-W.%20Lee,%20Nature.%20Photon.,%206,%20105-110%20(2012).pdf

Extremely efficient flexible organic light-emitting diodes with modified graphene anode

The past couple of years have witnessed a remarkable burst in the development of organic field-effect transistors (OFETs), with a number of organic semiconductors surpassing the benchmark mobility of 10 cm2/(V s). In this perspective, we highlight some of the major milestones along the way to provide a historical view of OFET development, introduce the integrated molecular design concepts and process engineering approaches that lead to the current success, and identify the challenges ahead to make OFETs applicable in real applications.

Integrated materials design of organic semiconductors for field-effect transistors

Fluorescence-baseddetection is gaining increasing attention owing to its highsensitivity, simplicity, short response time, and its ability to beemployed both in solution and solid phase. Numerousp-electron-rich fluorescent conjugated polymers have beensynthesized, and are used in the detection of trace amounts ofnitro aromatics.

Highly selective detection of nitro explosives by a luminescent metal-organic framework.

Multibit Storage of Organic Thin‐Film Field‐Effect Transistors

With the aim to develop new tetraphenylethylene (TPE)-based conjugated hyperbranched polymer, TPE units, one famous aggregation-induced emission (AIE) active group, are utilized to construct hyperbranched polymers with three other aromatic blocks, through an "A2+B4" approach by using one-pot Suzuki polycondensation reaction. These three hyperbranched polymers exhibit interesting AIEE behavior and act as explosive chemsensors with high sensitivity both in the nanoparticles and solid states. This is the first report of the AIE activity of the TPE-based conjugated hyperbranched polymers. Their corresponding PLED devices also demonstrate good performance.

Novel functional conjugative hyperbranched polymers with aggregation-induced emission: synthesis through one-pot "A2+B4" polymerization and application as explosive chemsensors and PLEDs.

In this paper, tetraphenylethylene (TPE) units, a well-known aggregation-induced emission (AIE) active group, are utilized to construct the hyperbranched polymer HP-TPE-Cz with carbazole moieties, a good hole-transporting and electroluminescent group, through an “A2 + B4” approach by using a one-pot Suzuki polycondensation reaction. For comparison, its analog linear polymer LP-TPE-Cz, also constructed from these two moieties, was prepared. These two polymers exhibit interesting aggregation-induced emission enhanced (AIEE) behavior and act as explosive chemosensors with high sensitivity both as nanoparticles and in solid state, due to the presence of TPE units. Also, the HP-TPE-Cz PLED device exhibited a remarkably enhanced current efficiency (2.13 cd A−1) and luminescence efficiency (5914 cd m−2), compared with its analog linear polymer LP-TPE-Cz (1.04 cd A−1, 1654 cd m−2).

A conjugated hyperbranched polymer constructed from carbazole and tetraphenylethylene moieties: convenient synthesis through one-pot “A2 + B4” Suzuki polymerization, aggregation-induced enhanced emission, and application as explosive chemosensors and PLEDs

Six blue AIE luminogens, Py-2pTPE, Py-2mTPE, Py-2TP, Py-2TF, Py-2NTF and Py-2F, have been successfully synthesized, which exhibit sky blue (484 nm) to deep blue (444 nm) emissions in accordance with the different introduced aromatic substituents on the pyrene core and the different linkage modes. Furthermore, Py-2pTPE and Py-2mTPE show interesting mechanochromism effects, inherited from TPE-pBr and TPE-mBr, respectively. When fabricated as emitters in OLEDs, all of the six AIEgens demonstrate blue emissions and good EL performances, among which, Py-2TP shows the best device performance with an ηEQE,max up to 3.46% at a CIE coordinate of (0.15, 0.09).

Blue pyrene-based AIEgens: inhibited intermolecular π–π stacking through the introduction of substituents with controllable intramolecular conjugation, and high external quantum efficiencies up to 3.46% in non-doped OLEDs

Shanghui Ye

Papers

Multibit Storage of Organic Thin‐Film Field‐Effect Transistors

Novel functional conjugative hyperbranched polymers with aggregation-induced emission: synthesis through one-pot "A2+B4" polymerization and application as explosive chemsensors and PLEDs.

A conjugated hyperbranched polymer constructed from carbazole and tetraphenylethylene moieties: convenient synthesis through one-pot “A2 + B4” Suzuki polymerization, aggregation-induced enhanced emission, and application as explosive chemosensors and PLEDs

Blue pyrene-based AIEgens: inhibited intermolecular π–π stacking through the introduction of substituents with controllable intramolecular conjugation, and high external quantum efficiencies up to 3.46% in non-doped OLEDs

Optimizing Single‐Walled Carbon Nanotube Films for Applications in Electroluminescent Devices