Han Nie

Rational Design of Aggregation-Induced Emission Luminogen with Weak Electron Donor–Acceptor Interaction to Achieve Highly Efficient Undoped Bilayer OLEDs

In this work, two tailored luminogens (TPE-NB and TPE-PNPB) consisting of tetraphenylethene (TPE), diphenylamino, and dimesitylboryl as a π-conjugated linkage, electron donor, and electron acceptor, respectively, are synthesized and characterized. Their thermal stabilities, photophysical properties, solvachromism, fluorescence decays, electronic structures, electrochemical behaviors, and electroluminescence (EL) properties are investigated systematically, and the impacts of electron donor-acceptor (D-A) interaction on optoelectronic properties are discussed. Due to the presence of a TPE unit, both luminogens show aggregation-induced emission, but strong D-A interaction causes a decrease in emission efficiency and red-shifts in photoluminescence and EL emissions. The luminogen, TPE-PNPB, with a weak D-A interaction fluoresces strongly in solid film with a high fluorescence quantum yield of 94%. The trilayer OLED [ITO/NPB (60 nm)/TPE-PNPB (20 nm)/TPBi (40 nm)/LiF (1 nm)/Al (100 nm)] utilizing TPE-PNPB as a light emitter shows a peak luminance of 49 993 cd m(-2) and high EL efficiencies up to 15.7 cd A(-1), 12.9 lm W(-1), and 5.12%. The bilayer OLED [ITO/TPE-PNPB (80 nm)/TPBi (40 nm)/LiF (1 nm)/Al (100 nm)] adopting TPE-PNPB as a light emitter and hole transporter simultaneously affords even better EL efficiencies of 16.2 cd A(-1), 14.4 lm W(-1), and 5.35% in ambient air, revealing that TPE-PNPB is an eximious p-type light emitter.

Highly Efficient Nondoped OLEDs with Negligible Efficiency Roll-Off Fabricated from Aggregation-Induced Delayed Fluorescence Luminogens

Purely organic emitters that can efficiently utilize triplet excitons are highly desired to cut the cost of organic light-emitting diodes (OLEDs), but most of them require complicated doping techniques for their fabrication and suffer from severe efficiency roll-off. Herein, we developed novel luminogens with weak emission and negligible delayed fluorescence in solution but strong emission with prominent delayed components upon aggregate formation, giving rise to aggregation-induced delayed fluorescence (AIDF). The concentration-caused emission quenching and exciton annihilation are well-suppressed, which leads to high emission efficiencies and efficient exciton utilization in neat films. Their nondoped OLEDs provide excellent electroluminescence efficiencies of 59.1 cd A-1 , 65.7 lm W-1 , and 18.4 %, and a negligible current efficiency roll-off of 1.2 % at 1000 cd m-2 . Exploring AIDF luminogens for the construction of nondoped OLEDs could be a promising strategy to advance device efficiency and stability.

Conjugation versus rotation: good conjugation weakens the aggregation-induced emission effect of siloles

Incorporation of polycyclic aromatic hydrocarbons into siloles enhances their light emission in solutions but lowers emission efficiency in the aggregated state. The competitive interaction between conjugation and rotation is thus studied.

Multichannel Conductance of Folded Single‐Molecule Wires Aided by Through‐Space Conjugation

Deciphering charge transport through multichannel pathways in single-molecule junctions is of high importance to construct nanoscale electronic devices and deepen insight into biological redox processes. Herein, we report two tailor-made folded single-molecule wires featuring intramolecular π-π stacking interactions. The scanning tunneling microscope (STM) based break-junction technique and theoretical calculations show that through-bond and through-space conjugations are integrated into one single-molecule wire, allowing for two simultaneous conducting channels in a single-molecule junction. These folded molecules with stable π-π stacking interaction offer conceptual advances in single-molecule multichannel conductance, and are perfect models for conductance studies in biological systems, organic thin films, and π-stacked columnar aggregates.

Triphenylamine-functionalized tetraphenylpyrazine: facile preparation and multifaceted functionalities

Aggregation-induced emission (AIE) is a unique photo-physical phenomenon and has become an emerging and hot research area. With the enthusiastic efforts paid by researchers, hundreds of AIE-active luminogens (AIEgens) have been generated but heterocyclic AIEgens are rarely reported. Recently, we enriched the family of AIEgens and reported a pyrazine-based AIEgen of tetraphenylpyrazine (TPP), which could be facilely functionalized by a post-synthetic strategy. In this work, we further expanded the TPP-based AIE system by covalently attaching one, two or four electron-donating triphenylamine moieties to the TPP core via Suzuki coupling, and TPP–TPA, TPP–2TPA and TPP–4TPA were produced, respectively. Thanks to their donor-π-acceptor structures, these luminogens exhibit multi-functional properties, such as excellent thermal stability (up to 504 °C), large molar absorptivity, bright emission in the solid state (quantum yields up to 35.2%), solvatochromism, and high two-photon absorption cross-sections (up to 480 GM). Furthermore, using TPP–TPA as the emitting layer, a triple-layer device was fabricated and a turn-on voltage, maximum luminance, current efficiency, power efficiency, and external quantum efficiency of 3.7 V, 17 459 cd m−2, 5.49 cd A−1, 3.18 lm W−1 and 2.88% were realized, respectively. These results indicate a huge potential to develop high-tech applications based on these TPP-based AIEgens.

Integration of aggregation-induced emission and delayed fluorescence into electronic donor–acceptor conjugates

A series of luminogens comprised electron donors and acceptors are found to possess two types of interesting photophysical processes of aggregation-induced emission (AIE) and delayed fluorescence. According to theory calculation, restriction of intramolecular motions accounts for their AIE characteristics. Moreover, a separated distribution of the HOMOs and the LUMOs of these luminogens leads to small ΔEST values and therefore delayed fluorescence.

Tetraphenylfuran: aggregation-induced emission or aggregation-caused quenching?

Tetraphenylfuran (TPF) and its control molecule tetraphenylthiophene (TPT), which are structurally similar to the aggregation-induced emission (AIE) active 2,3,4,5-tetraphenylsilole, were synthesized. Surprisingly, investigation of its photo-physical properties showed that TPF exhibits the aggregation-caused quenching effect instead of AIE characteristics, whereas TPT exhibits a quite weak AIE effect. Combining experimental results and theoretical calculations, this phenomenon was concluded to be co-caused by the restriction of intramolecular rotation (RIR), the mechanism of AIE, and the conjugation effect. Thus, this work provides an insight into RIR, which will greatly promote the development of AIE.

Improving Electron Mobility of Tetraphenylethene-Based AIEgens to Fabricate Nondoped Organic Light-Emitting Diodes with Remarkably High Luminance and Efficiency

Robust light-emitting materials with strong solid-state fluorescence as well as fast and balanced carrier transporting ability are crucial to achieve high-performance organic light-emitting diodes (OLEDs). In this contribution, two linear tetraphenylethene (TPE) derivatives (TPE-TPAPBI and TPE-DPBI) that are functionalized with hole-transporting triphenylamine and/or electron-transporting 1,2-diphenyl-1H-benzimidazole groups are synthesized and fully characterized. Both TPE-TPAPBI and TPE-DPBI have aggregation-induced emission attributes and excellent photoluminescence quantum yields approaching 100% in vacuum deposited films. They also possess good thermal property, giving high decomposition temperatures (480 and 483 °C) and glass-transition temperatures (141 and 157 °C). TPE-TPAPBI and TPE-DPBI present high electron mobilities of 1.80 × 10(-5) and 1.30 × 10(-4) cm(2) V (-1) s(-1), respectively, at an electric field of 3.6 × 10(5) V cm(-1), which are comparable or even superior to that of 1,3,5-tri(1-phenylbenzimidazol-2-yl)benzene. The nondoped OLED device employing TPE-TPAPBI as active layer performs outstandingly, affording ultrahigh luminance of 125 300 cd m(-2), and excellent maximum external quantum, power and current efficiencies of 5.8%, 14.6 lm W(-1), and 16.8 cd A(-1), respectively, with very small roll-offs, demonstrating that TPE-TPAPBI is a highly promising luminescent material for nondoped OLEDs.

A Red to Near‐IR Fluorogen: Aggregation‐Induced Emission, Large Stokes Shift, High Solid Efficiency and Application in Cell‐Imaging

A tetraphenylethene (TPE) derivative modified with the strong electron acceptor 2-dicyano-methylene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran (TCF) was obtained in high yield by a simple two-step reaction. The resultant TPE-TCF showed evident aggregation-induced emission (AIE) features and pronounced solvatochromic behavior. Changing the solvent from apolar cyclohexane to highly polar acetonitrile, the emission peak shifted from 560 to 680 nm (120 nm redshift). In an acetonitrile solution and in the solid powder, the Stokes shifts are as large as 230 and 190 nm, respectively. The solid film emits red to near-IR (red-NIR) fluorescence with an emission peak at 670 nm and a quantum efficiency of 24.8 %. Taking the advantages of red-NIR emission and high efficiency, nanoparticles (NPs) of TPE-TCF were fabricated by using tat-modified 1,2-distearoylsn-glycero-3-phosphor-ethanol-amine-N-[methoxy-(polyethyl-eneglycol)-2000] as the encapsulation matrix. The obtained NPs showed perfect membrane penetrability and high fluorescent imaging quality of cell cytoplasm. Upon co-incubation with 4,6-diamidino-2-phenylindole (DAPI) in the presence of tritons, the capsulated TPE-TCF nanoparticles could enter into the nucleus and displayed similar staining properties to those of DAPI.

High Fluorescence Efficiencies and Large Stokes Shifts of Folded Fluorophores Consisting of a Pair of Alkenyl-Tethered, π-Stacked Oligo-p-phenylenes

A series of pure hydrocarbon fluorophores containing a pair of π-stacked oligo-p-phenylenes have been synthesized and analyzed by NMR and X-ray crystallography. They show good fluorescence in solutions and enhanced fluorescence in the aggregated state. Large Stokes shifts (up to 214 nm) have been achieved in these folded fluorophores in virtue of intramolecular energy transfer, and balanced structural rigidity and flexibility. These folded fluorophores provide perfect models for understanding the energy and charge transfer process in π-stacked systems.