Structural Engineering of Red Luminogens to Realize High Emission Efficiency through ACQ-to-AIE Transformation.

Deep red/near-infrared (NIR, >650 nm) emissive organic luminophores with aggregation-induced emission (AIE) behaviours have emerged as promising candidates for applications in optoelectronic devices and biological fields. However, the molecular design philosophy for AIE luminogens (AIEgens) with narrow band gaps are rarely explored. Herein, we rationally designed two red organic luminophores, FITPA and FIMPA, by considering the enlargement of transition dipole moment in the charge-transfer state and the transformation from aggregation-caused quenching (ACQ) to AIE. The transition dipole moments were effectively enhanced with a "V-shaped" molecular configuration. Meanwhile, the ACQ-to-AIE transformation from FITPA to FIMPA was induced by a methoxy-substitution strategy. The experimental and theoretical results demonstrated that the ACQ-to-AIE transformation originated from a crystallization-induced emission (CIE) effect because of additional weak interactions in the aggregate state introduced by methoxy groups. Owing to the enhanced transition dipole moment and AIE behaviour, FIMPA presented intense luminescence covering the red-to-NIR region, with a photoluminescence quantum yield (PLQY) of up to 38 % in solid state. The promising cell-imaging performance further verified the great potential of FIMPA in biological applications. These results provide a guideline for the development of red and NIR AIEgens through comprehensive consideration of both the effect of molecular structure and molecular interactions in aggregate states.

Visualizing Assembly Dynamics of All-Liquid 3D Architectures.

To better exploit all-liquid 3D architectures, it is essential to understand dynamic processes that occur during printing one liquid in a second immiscible liquid. Here, the interfacial assembly and transition of 5,10,15,20-tetrakis(4-sulfonatophenyl) porphyrin (H6 TPPS) over time provides an opportunity to monitor the interfacial behavior of nanoparticle surfactants (NPSs) during all-liquid printing. The formation of J-aggregates of H4 TPPS2- at the interface and the interfacial conversion of the J-aggregates of H4 TPPS2- to H-aggregates of H2 TPPS4- is demonstrated by interfacial rheology and in situ atomic force microscopy. Equally important are the chromogenic changes that are characteristic of the state of aggregation, where J-aggregates are green in color and H-aggregates are red in color. In all-liquid 3D printed structures, the conversion in the aggregate state with time is reflected in a spatially varying change in the color, providing a simple, direct means of assessing the aggregation state of the molecules and the mechanical properties of the assemblies, linking a macroscopic observable (color) to mechanical properties.

Visualizing Interfacial Jamming Using an Aggregation-Induced-Emission Molecular Reporter.

With the interfacial jamming of nanoparticles (NPs), a load-bearing network of NPs forms as the areal density of NPs increases, converting the assembly from a liquid-like into a solid-like assembly. Unlike vitrification, the lineal packing of the NPs in the network is denser, while the remaining NPs can remain in a liquid-like state. It is a challenge to determine the point at which the assemblies jam, since both jamming and vitrification lead to a solid-like behavior of the assemblies. Herein, we show a real-time fluorescence imaging method to probe the evolution of the interfacial dynamics of NP surfactants at the water/oil interface using aggregation-induced emission (AIE) as a reporter for the transition of the assemblies into the jammed state. The AIEgens show typical fluorescence behavior at densities at which they can move and rotate. However, when aggregation of these fluorophores occurs, the smaller intermolecular separation distance arrests rotation, and a significant enhancement in the fluorescence intensity occurs.

Surfactant-Induced Interfacial Aggregation of Porphyrins for Structuring Color-Tunable Liquids.

Locking nonequilibrium shapes of liquids into targeted architectures by interfacial jamming of nanoparticles is an emerging area in material science. 5,10,15,20-tetrakis(4-sulfonatophenyl) porphyrin (H6 TPPS) shows three different aggregation states that present an absorption imaging platform to monitor the assembly and jamming of supramolecular polymer surfactants (SPSs) at the liquid/liquid interface. The interfacial interconversion of H6 TPPS, specifically H4 TPPS2- dissolved in water, from J- to an H-aggregation was induced by strong electrostatic interactions with amine-terminated polystyrene dissolved in toluene at the water/toluene interface. This resulted in color-tunable liquids due to interfacial jamming of the SPSs formed between H4 TPPS2- and amine-terminated polystyrene. However, the formed SPSs cannot lock in nonequilibrium shapes of liquids. In addition, a self-wrinkling behavior was observed when amphiphilic triblock copolymers of PS-block-poly(2-vinylpyridine)-block-poly(ethylene oxide) were used to interact with H4 TPPS2- . Subsequently, the SPSs formed can lock in nonequilibrium shapes of liquids.

Stabilizing Liquids Using Interfacial Supramolecular Polymerization.

The strong electrostatic interactions at the oil-water interface between a small molecule, 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin, H6 TPPS, dissolved in water, and an amine terminated hydrophobic polymer dissolved in oil are shown to produce a supramolecular polymer surfactant (SPS) of H6 TPPS at the interface with a binding energy that is sufficiently strong to allow an intermolecular aggregation of the supramolecular polymers. SPSs at the oil-water interface are confirmed by in situ real-space atomic force microcopy imaging. The assemblies of these aggregates can jam at the interface, opening a novel route to kinetically trap the liquids in non-equilibrium shapes. The elastic film, comprised of SPSs, wrinkles upon compression, providing a strategy to stabilize liquids in non-equilibrium shapes.

Synthesis, physical properties, and light-emitting diode performance of phenazine-based derivatives with three, five, and nine fused six-membered rings.

Realizing the control of emission colors of single molecules is very important in the development of full-color emitting materials. Herein, three novel phenazine derivatives (2,3,7,8-tetrakis(decyloxy)phenazine (2a), 2,3-didecyloxy-5,14-diaza-7,12-dioxo-9,10- dicyanopentacene (2b), and 2,3,13,14-tetradecyloxy-5,11,16,22-tetraaza-7,9,18,20-tetraoxo-8,19-dicyanoenneacene (2c)) have been successfully synthesized and fully characterized. Compound 2c can emit blue light in toluene solution (450 nm), green light in the powder/film state (502/562 nm), and red light in the 2c/TFA state (610 nm). The OLED with 2c emits a strong green light at a peak of 536 nm with a maximum luminance of the OLED of about 8600 cd m(-2), which indicates that 2c could be a promising fluorescent dye for OLED applications.

Synthesis, characterization, and nonvolatile ternary memory behavior of a larger heteroacene with nine linearly fused rings and two different heteroatoms.

To achieve ultrahigh density memory devices with the capacity of 3(n) or larger, organic materials with multilevel stable states are highly desirable. Here, we reported a novel larger stable heteroacene, 2,3,13,14-tetradecyloxy-5,11,16,22-tetraaza-6,10,17,21-tetrachloro-7,9,18,20-tetraoxa-8,19-dicyanoenneacene (CDPzN), which has two different types of heteroatoms (O and N) and nine linearly fused rings. The sandwich-structure memory devices based on CDPzN exhibited excellent ternary memory behaviors with high ON2/ON1/OFF current ratios of 10(6.3)/10(4.3)/1 and good stability for these three states.

Continuous, autonomous subsurface cargo shuttling by nature-inspired meniscus-climbing systems.

Water-walking insects can harness capillary forces by changing their body posture to climb or descend the meniscus between the surface of water and a solid object. Controlling surface tension in this manner is necessary for predation, escape and survival. Inspired by this behaviour, we demonstrate autonomous, aqueous-based synthetic systems that overcome the meniscus barrier and shuttle cargo subsurface to and from a landing site and a targeted drop-off site. We change the sign of the contact angle of a coacervate sac containing an aqueous phase or of a hydrogel droplet hanging from the surface by controlling the normal force acting on the sac or droplet. The cyclic buoyancy-induced cargo shuttling occurs continuously, as long as the supply of reactants diffusing to the sac or droplet from the surrounding aqueous phase is not exhausted. These findings may lead to potential applications in autonomously driven reaction or delivery systems and micro-/milli-robotics.

Naphthalimide-Based Hydrazone Derivatives: Synthesis, Mechanochromism in the Solid State and Response to Ions in Dilute Solutions.

Molecules showing mechanochromic luminescence (MCL) are promising for use in the in the fields of sensing and probes. We report the design and synthesis of new naphthalimide-based hydrazone derivatives, NI-TPE and NI-3BA. Both the luminogens are weakly emissive with s Φf =0.3 % and 0.5 % respectively when aggregated in amorphous states as strong π-π stacking and intermolecular interaction prevent luminescence. On the contrary, in the crystalline state, single crystal analysis of two derivatives shows that nonradiative decay is reduced or inhibited by molecular stacking modes and intermolecular interactions. Increases of fluorescence emission intensity to s Φf =5.5 % and 6.0 % upon solvent evaporation are attributed to weak π-π overlapping and hydrogen bonding (N-H ⋅⋅⋅ O, distance 2.99 Å), which are beneficial to the formation of molecules with a loose packing. At the same time, the packing modes that the two derivatives adopt in the crystal lattice are destroyed to result in a low solid-state fluorescence quantum yield and a bathochromic shift of 23-25 nm upon grinding. All these factors cause the two derivatives show an unusual "turn off" MCL phenomenon. The fluorescence emission, its pH reversibility, and selective response to fluoride and acetate ions of up to 91-93 % in dilute solutions were also demonstrated.

Conductive Thin Films over Large Areas by Supramolecular Self-Assembly.

We report a "one-step" method for preparing conductive thin films with cylindrical microdomains oriented normal to the surface over large areas using the supramolecular assembly of poly(styrene-block-4-vinylpyridine) (PS19-b-P4VP5) and 5,10,15,20-tetrakis(4-hydroxyphenyl)-21H,23H-porphine (HOTPP). HOTPP interacts with the P4VP block by hydrogen bonding between the hydroxyl group of HOTPP and pyridine ring of PS19-b-P4VP5, forming cylindrical P4VP(HOTPP) domains having an average diameter of ∼17 nm in a PS matrix. Dynamic light scattering, contact angle, and in situ grazing incidence small-angle X-ray scattering measurements show a morphological transition from spherical micelles in solution to cylindrical microdomains oriented normal to the substrate surface during the drying process. From the dependence of current on voltage, an average current of ∼4.0 nA is found to pass through a single microdomain, pointing to a promising route for organic semiconductor device applications.

Synthesis, Physical Properties and Memory Device Application of a Twelve-Ring Fused Twistheteroacene.

Developing new organic conjugated materials for high density memory devices is highly desirable. In this research, a novel donor-acceptor-type twelve-ring fused twistheteroacene, 2,7,19,24-tetra-tert-butyl-13,30-didodecyl-9,17,26,34-tetraphenyl benzo[8',9']triphenyleno[2',3':7,8]dibenzo[b,e][1,4]dioxino[1,2,3,4-lmn]dibenzo[6',7':10',11']tetraceno[2',3':5,6][1,4]dioxino[2,3-f][3,8]phenanthroline-12,14,29,31(13H,30H)-tetraone (DPyN) has been synthesized and characterized. It displays high thermal stability, possesses a broad absorption band centered at 510 and 538 nm, and emits red fluorescence in organic solvents. A solution-processed memory device with DPyN as an active element shows an excellent memory performance with an ON/OFF current ratio of 103.46 :1 and a threshold voltage of -2.44 V.

Azaacenes as active elements for sensing and bio applications.

Since azaacenes have electron-deficient backbones and lone-pair electrons on nitrogen centers, they can efficiently detect the target molecules or ions through supramolecular interactions such as anion-π attractions and coordinate bonding. These special features make azaacenes very designable for various sensors, which can be further used in the bio field. In this review, we will summarize the recent progress in the applications of azaacenes in sensing and bio fields. We believe that a rapid development in the research of sensors and bio applications based on azaacenes will be witnessed in the coming years due to their tuneable structures, optical properties and binding abilities.

Nanostructured Conjugated Polymers for Energy-Related Applications beyond Solar Cells.

To meet the ever-increasing requirements for the next generation of sustainable and versatile energy-related devices, conjugated polymers, which have potential advantages over small molecules and inorganic materials, are among the most promising types of green candidates. The properties of conjugated polymers can be tuned through modification of the structure and incorporation of different functional moieties. In addition, superior performances can be achieved as a result of the advantages of nanostructures, such as their large surface areas and the shortened pathways for charge transfer. Therefore, nanostructured conjugated polymers with different properties can be obtained to be applied in different energy-related organic devices. This review focuses on the application and performance of the recently reported nanostructured conjugated polymers for high-performance devices, including rechargeable lithium batteries, microbial fuel cells (MFCs), thermoelectric generators, and photocatalytic systems. The design strategies, reaction mechanisms, advantages, and limitations of nanostructured conjugated polymers are further discussed in each section. Finally, possible routes to improve the performances of the current systems are also included in the conclusion.

Improving the Performance of Lithium-Sulfur Batteries by Employing Polyimide Particles as Hosting Matrixes.

Sulfur cathodes with four polyimide (PI) compounds as hosting matrixes have been prepared through a simple one-step approach. These four PIs-S composites exhibited higher sulfur utilization and better cycling stability than pure sulfur. At a current rate of 300 mA g(-1), the initial discharge capacities of PI-1S, PI-2S, PI-3S, and BBLS reached 1120, 1100, 1150, and 1040 mAh g(-1), respectively. After the 30th cycle, PI-1S, PI-2S, PI-3S, BBLS and pristine sulfur powder still remained discharge capacities of 715, 673, 729, 643, and 550 mAh g(-1). Especially, PI-1S and PI-3S cathodes exhibit excellent cycling stability with the discharge capacities of 522 and 574 mAh g(-1) at the 450th cycle, respectively.

An Azaacene Derivative as Promising Electron-Transport Layer for Inverted Perovskite Solar Cells.

It is highly desirable to develop novel n-type organic small molecules as an efficient electron-transport layer (ETL) for the replacement of PCBM to obtain high-performance metal-oxide-free, solution-processed inverted perovskite solar cells (PSCs) because this type of solar cells with a low-temperature and solution-based process would make their fabrication more feasible and practical. In this research, the new azaacene QCAPZ has been synthesized and employed as non-fullerene ETL material for inverted PSCs through a solution-based process without the need for additional dopants or additives. The as-fabricated inverted PSCs show a power conversion efficiency up to 10.26 %. Our results clearly suggest that larger azaacenes could be promising electron-transport materials to achieve high-performance solution-processed inverted PSCs.

1,5,9-Triaza-2,6,10-triphenylboracoronene: BN-embedded analogue of coronene.

A novel BN-fused coronene derivative 1,5,9-triaza-2,6,10-triphenylboracoronene (1) has been successfully synthesized in one step from 2,3,6,7,9,10-hexamethoxy-1,5,9-triamino-triphenylene. Compound 1 has been investigated using photophysical, electrochemical, and molecular simulation methods. Interestingly, three phenyl groups at B centers in compound 1 can be replaced by hydroxyl units stepwise through hydroxylation in wet organic solvents, leading to changes in the packing and physical properties.

A new V-shaped organic fluorescent compound integrated with crystallization-induced emission enhancement and intramolecular charge transfer.

The emission behavior of a new V-shaped organic fluorescent compound (p,p'-bis(2-aryl-1,3,4-oxadiazol-5-yl)diphenyl sulfone (OZA-SO)), consisting of diethylamino (donor) and sulfone (acceptor) units, has been studied in various polar solvents and with different morphologies. As expected, there is the gradual transition from the locally excited state to the intramolecular charge-transfer (ICT) state with the increasing solvent polarity. The photoluminescence intensity of OZA-SO initially decreases with a low water fraction (f(w)), owing to ICT effect, and then increases with a high f(w), owing to crystallization-induced emission enhancement. At the same time, the fluorescence lifetime of OZA-SO increases from 0.062 ns in dimethylformamide (DMF) to 5.80 ns in a solution containing 90 % water, and then to 7.49 ns in a solution containing 60 % water. Furthermore, the solid-state emission of OZA-SO can be tuned reversibly from green to yellow by fuming/grinding or fuming/heating owing to morphological changes. This color-switchable feature of OZA-SO may have potential applications in optical-recording and temperature-sensing materials.

Initiator-lightened polymers: preparation of end-functionalized polymers by ATRP and their intramolecular charge transfer and aggregation-induced emission.

A simple strategy to prepare AIE polymers is invented using an AIE initiator for atom transfer radical polymerization. The dual photoresponse by intramolecular charge-transfer and luminogen aggregation of the initiator is well-realized and even enlarged after polymerization, due to the linkage of polymer chains.