Remarkable Off-On Tunable Solid-State Luminescence by the Regulation of Pyrene Dimer.

It is always a challenge to achieve "off-on" luminescent switch by regulating non-covalent interactions. Herein, we report a unique strategy for constructing high performance "off-on" tunable luminescent materials utilizing a novel molecule (TFPA) consist of pyrene and cyanostilbene. The pristine crystal of TFPA is almost non-emissive. Upon grinding/UV irradiation, an obvious luminescence enhancement is observed. Theoretical and experimental results revealed the underlying mechanism of this intriguing "off-on" switching behavior. The non-emissive crystal consists of ordered H-aggregates, with adjacent two molecules stacked in an anti-parallel manner and no overlapped area in pyrene moieties. When external force is applied by grinding or internal force is introduced through the photoisomerization, the dimer structures are facilitated with shorter intermolecular distances and better overlapping of pyrene moieties. In addition, the "on" state can recover to "off" state under thermal annealing, showing good reversibility and applicability in intelligence material. The present results promote an in-depth insight between packing structure and photophysical property, and offer an effective strategy for the construction of luminescence "off-on" switching materials, toward the development of stimuli-responsive luminescent materials for anti-counterfeiting.

Frontier Molecular Orbital Engineering: Constructing Highly Efficient Narrowband Organic Electroluminescent Materials.

It is of great strategic significance to develop highly efficient narrowband organic electroluminescent materials that can be utilized to manufacture ultra-high-definition (UHD) displays and meet or approach the requirements of Broadcast Television 2020 (B.T.2020) color gamut standards. This motif poses challenges for molecular design and synthesis, especially for developing generality, diversity, scalability, and robustness of molecular structures. The emergence of multiple resonance thermally activated delayed fluorescence (MR-TADF) emitters has ingeniously solved the problems and demonstrated bright application prospects in the field of UHD displays, sparking a research boom. This Minireview summarizes the research endeavors of narrowband organic electroluminescent materials, with emphasis on the tremendous contribution of frontier molecular orbital engineering (FMOE) strategy. It combines the outstanding advantages of MR framework and donor-acceptor (D-A) structure, and can achieve red-shift and narrowband emission simultaneously, which is of great significance in the development of long-wavelength narrowband emitters with emission maxima especially exceeding 500 nm. We hope that this Minireview would provide some inspiration for what could transpire in the future.

Morphology-dependent photoresponsive behaviors of a self-assembled system based on a single cyanostilbene derivative.

In recent years, photoresponsive supramolecular self-assemblies have shown great potential in various fields. However, it is still a great challenge to integrate and control multiple photoresponsive behaviors in a self-assembled system. Herein, we design a novel cyanostilbene-based molecule VOE. In the aggregated state, it has different photoresponsive behaviors under different morphologies. When VOE molecules are dispersed in a 70% H2O/THF mixture, two different assembly morphologies are obtained as the aging time changes. One is weakly emissive nanoparticles with amorphous packing arrangements, and the other is highly emissive microbelts with well-ordered stacking modes. When they are irradiated with blue light (420 nm), the disordered assembly structure of nanoparticles leads to a [2+2] cycloaddition reaction, while a Z/E isomerization reaction occurs in ordered packed microbelts. Therefore, we can use a self-assembled system to generate two different morphologies, enabling completely different emissions and photoresponsive behaviors.

Tuning Organic Microcrystal Morphologies through Crystal Engineering Strategies toward Anisotropic Optical Waveguide.

The construction of organic optoelectronic materials with desirable size and morphology remains a challenge now. Crystal engineering strategies (polymorphs and cocrystals) provide convenience for tailoring molecular packing and further controlling the growth morphology and photofunctionality of materials. Herein, we prepare polymorphic 2D plate crystals and 3D microhelixes by assembly of a cyanostilbene derivative (2-(3',5'-bis(trifluoromethyl)-biphenyl-4-yl)-3-(4-(pyridin-4-yl)phenyl)acrylonitrile, CF3-CN-Py). The former emits blue emission, while the latter emits green emission. Different crystallization environments contribute to the adjustable morphologies. Then, novel cocrystals are fabricated with the introduction of 1,4-diiodotetrafluorobenzene (FDIB) to CF3-CN-Py. Both molecular conformation and packing are totally changed in the cocrystal system. Such cocrystal displays a 1D sky-blue emissive rod shape on account of a long-range ordered π-stacking of molecules. In addition, the 2D plate crystal and 1D rod cocrystal are further applied to optical waveguides. In the plate crystal, a packing of transition dipole moment (µ) inclined to the upper surface leads to an anisotropic optical waveguide. In the cocrystal, owing to the nearly horizontal µ orientation, the cocrystal exhibits light propagation along the primary growth direction and a low optical loss coefficient. The present study supplies an effective way to construct materials with controlled morphology and optical waveguide.

Programmable photoresponsive materials based on a single molecule via distinct topochemical reactions.

Engineering the preorganization of photoactive units remains a big challenge in solid-state photochemistry research. It is of not only theoretical importance in the construction of topochemical reactions but also technological significance in the fabrication of advanced materials. Here, a cyanostilbene derivative, (Z)-2-(3,5-bis(trifluoromethyl)phenyl)-3-(naphthalen-2-yl) acrylonitrile (BNA), was crystallized into two polymorphs under different conditions. The two crystals, BNA-α and BNA-ß, have totally different intra-π-dimer and inter-π-dimer hierarchical architectures on the basis of a very simple monomer, which provides them with distinct reactivities, functions and photoresponsive properties. Firstly, two different types of solid-state [2 + 2] photocycloaddition reaction: (i) a typical olefin-olefin cycloaddition reaction within the symmetric π-dimers of BNA-α and (ii) an unusual olefin-aromatic ring cycloaddition reaction within the offset π-dimers of BNA-ß have been observed, respectively. Secondly, the crystal of BNA-α can be bent to 90° without any fracture, exhibiting outstanding flexibility upon UV irradiation, while the reversible photocycloaddition/thermal cleavage process (below 100 °C) accompanied by unique fluorescence changes can be achieved in the crystal of BNA-ß. Finally, micro-scale photoactuators and light-writable anti-counterfeiting materials have been successfully fabricated. This work paves a simple way to construct smart materials through a bottom-up way that is realized by manipulating hierarchical architectures in the solid state.

White-light-emitting hydrogels with self-healing properties and adjustable emission colors.

White-light-emitting soft materials with self-healing properties show extensive applications in many fields. Herein, a novel self-healing hydrogel is successfully fabricated using oxidized dextran (Odex) and dithiodipropionate dihydrazide (TPH). Carbon dots (CDs), Riboflavin (Ri) and Rhodamine B (RhB) are incorporated into the gel matrix to produce white light emission through fluorescence resonance energy transfer (FRET) process, thus achieving excellent Commission Internationale de L'eclairage (CIE) coordinate value of (0.30, 0.33). The emission colors can be easily tuned via changing proportions of three emitters or the excitation wavelength. When the hydrogels are coated on an ultraviolet light-emitting diodes (UV LED), the hydrogel coating converts UV light to white light and repairs itself in 20 h while a hole is dug from it. Thanks to reversible exchanging reactions of acylhydrazone and disulfide bonds in hydrogel networks, the hydrogel coating exhibits perfect self-healing property in a wide range of pH (from 5 to 9 except for 7). The excellent emission and self-healing properties of hydrogels have great value in practical applications.

Tunable morphologies and emission of photosensitive supramolecular self-assemblies through positional and trans-cis isomerization.

Cyanostilbene units are widely attractive as photoresponsive supramolecular building blocks whose structures and emission can be modulated by trans-cis isomerization. Generally, the change of properties is related to the molecular structure of cyanostilbene, which is still unpredictable and needs to be explored. Herein, two benzene-1,3,5-tricarboxamide (BTA) based cyanostilbene derivatives with different cyano positions have been designed to investigate the emission as well as structural changes during the trans-cis photoisomerization process in monomer and aggregation states, respectively. In the monomer state, the derivative with cyano groups at the outer position, ß-BTTPA, exhibits obvious emission enhancement upon UV irradiation, while the other derivative (α-BTTPA) shows emission quenching. In addition, upon the formation of aggregates, ß-BTTPA forms nano-level fibers with blue-green emission, but α-BTTPA forms micron-level flat ribbons with blue emission. More importantly, also driven by the trans-cis photoisomerization, the self-assemblies show morphological transitions (ribbons/fibers to spheres) due to the fact that the equilibrium of the system is broken by the photoreactions. Such changes further contribute to emission switching as well as enhanced hydrophobic properties.

Multi-color tunable circularly polarized luminescence in one single AIE system.

Circularly polarized luminescence (CPL) materials with a large luminescence dissymmetry factor (g lum) and multi-color properties are very attractive. While multi-color tunable CPL can be realized by different organic dyes, the challenge of realizing both a higher g lum and multiple colors using a single component remains. Here, we design an aggregation-induced emission (AIE) fluorophore, which is a pyridine functionalized cyanostilbene attached to a chiral unit, and realize multi-color tunable CPL with a high g lum. The compound can self-assemble into a nanohelix and form both gel and xerogel films, exhibiting blue CPL with large g lum values of -3.0 × 10-2 and -1.7 × 10-2, respectively. With the assistance of pyridine protonation, the xerogel films exhibit red-shifted CPL signals from 480 nm to 530 nm, covering from blue via green and yellow to orange. Additionally, the g lum remains constant during the process. This work paves a simple and convenient way to construct multi-color tunable CPL materials using a single molecule.

2-Phenyl-3-(p-aminophenyl) Acrylonitrile: A Reactive Matrix for Sensitive and Selective Analysis of Glycans by MALDI-MS.

Analysis of glycans by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is usually limited by the intrinsically low abundance and low ionization efficiency of glycans. Aiming to enhance the ionization efficiency of glycans and simplify the sample preparation procedure during MALDI-MS analysis, we reported herein a novel reactive matrix, 2-phenyl-3-(p-aminophenyl) acrylonitrile (PAPAN), for sensitive and selective detection of glycans. PAPAN is a derivative of α-cyanocinnamic acid, which possesses high ionization efficiency in MALDI-MS. The PAPAN can react with the terminal aldehyde of glycans and thereby enable the significant enhancement of ionization efficiency of glycans. As a result, using PAPAN as a reactive matrix, the detection sensitivity for glycans was improved 100-fold compared with that using 2,5-dihydroxybenzoic acid (DHB) as the matrix. Meanwhile, the ionization of peptides can be significantly suppressed using PAPAN as the matrix, which allowed the selective detection of N-glycans from a deglycosylated tryptic digest of glycoprotein without any prepurification. Moreover, the PAPAN matrix also endowed the analysis of glycans with enhanced fragmentation during MS/MS analysis, which could facilitate glycan structure interpretation. Finally, PAPAN was successfully used for the analysis of N-glycome in human serum. Thus, a simple, sensitive, and selective method for the analysis of glycans has been achieved by using a novel reactive matrix, PAPAN.

Selective Cu(ii) sensing by a versatile AIE cyanostilbene-based gel system.

Cyanostilbene-based derivatives 1-3 were designed, synthesized and fully characterized. By screening their gelating abilities, we observed that the subtle difference in the position of the pyridine nitrogen greatly affected the resulting fluorescence and gelation properties. Notably, 1 was found to be a versatile ambidextrous gelator capable of forming organo-, hydro-, and Cu(ii) specific metallogels. Furthermore, a rare organogel-to-metallogel transformation at room temperature was also observed upon exposure of the 1-DMSO/H2O gel to aqueous Cu(ii). This process, accompanied by colour and fluorescence changes, provides an effective strategy for the preparation of novel sensing soft materials.

Effects of FGF2/FGFR1 Pathway on Expression of A1 Astrocytes After Infrasound Exposure.

Two types of reactive astrocytes, A1 and A2 astrocytes, are induced following neuroinflammation and ischemia. In this study, we evaluated the effects of the fibroblast growth factor (FGF)2/FGF receptor (FGFR)1 pathway on A1 and A2 astrocytes in the rat hippocampus using double-labeling immunofluorescence following infrasound exposure. A1 astrocytes were induced in the CA1 region of the hippocampus after exposure to infrasound for 3 days. The number of microglial cells was also increased, and we investigated if these might be responsible for the reactivity of A1 astrocytes. Accordingly, expression levels of C3 and Iba-1, as markers of A1 astrocytes and microglial cells, respectively, were both up-regulated in rat hippocampus following infrasound exposure, as demonstrated by western blot. We also explored the effect of the FGF2/FGFR1 pathway on A1 astrocyte reactivity by pretreating rats with FGF2 or the specific FGFR1 antagonist, PD173074. A1 astrocytes were gradually down-regulated by activation of the FGF2/FGFR1 pathway and were up-regulated by inhibition of the FGF2/FGFR1 pathway after infrasound damage. These results further our understanding of the role of reactive astrocytes in infrasound-induced central nervous system injury and will thus facilitate the development of new treatments for these injuries.

Highly Ordered Semiconducting Polymer Arrays for Sensitive Photodetectors.

Semiconducting conjugated polymers possess attractive optoelectronic properties and low-cost solution processability and are inherently mechanically flexible. However, the device performance is susceptible to the fabrication methods because of the relatively weak intermolecular interaction of the polymers and their inherent conformational and energetic disorder. An efficient fabrication technique for large-scale integration of high-quality polymer architectures is essential for realizing high-performance optoelectronic devices. Here, we report an efficient method for fabrication of polymer nanowire arrays with a precise position, a smooth surface, a homogeneous size, high crystallinity, and ordered molecular packing. The controllable dewetting dynamics on a template with asymmetric wettability permits the formation of discrete capillary bridges, resulting in the ordered molecular packing arising from unidirectional recession of the three-phase contact line. The high quality of nanowire architectures is evidenced by the morphological characteristics and hybrid edge-on and face-on molecular packing with high crystallinity. On the basis of these high-quality nanowire arrays, photodetectors with a responsivity of 84.7 A W-1 and detectivity of >1012 Jones are realized. Our results provide a platform for integration of high-quality polymer architectures for use in high-performance optoelectronic devices.

A cyanide-sensing detector in aqueous solution based on anion-π interaction-driven electron transfer.

A "turn on" fluorescent and colorimetric sensor, HAT(CN)6, was developed for the light-up detection of cyanide. It was implemented through its strong anion-π interaction, inducing thermal CN- → HAT(CN)6 electron transfer, to give the dianion product [HAT(CN)6]2-, which exhibits unexpected fluorescence. The sensor shows high selectivity, rapid response and a low detection limit towards CN- in aqueous solution, hence indicating its enormous potential in practical applications.

Multi-stimuli responsive supramolecular gels based on a D-π-A structural cyanostilbene derivative with aggregation induced emission properties.

Developing multi-stimuli responsive fluorescent gel materials in a single system remains challenging. Gelator molecules with classical fluorophores suffer from the aggregation-caused quenching (ACQ) effect, limiting their applications further. Herein, a novel V-shaped cyanostilbene-based molecule (BAPBIA) with aggregation induced emission (AIE) characteristics and great gelation ability was synthesized and was found to exhibit multi-stimuli responsive behaviors. Reversible gel-sol phase transitions together with emission quenching are realized in response to external stimuli including heat, light and fluoride ions. Especially, the introduction of a dimethylaniline group (donor) and a cyano group (acceptor) generates a D-π-A structure, further leading to an intramolecular charge transfer (ICT) effect, which enlarges the emission contrast with the variation of the distribution of charge. Thus, upon trifluoroacetic acid (TFA) triggered protonation of the dimethylaniline group, not only a gel-sol transition but also emission color switching (yellow-to-blue) is achieved due to the loss of the ICT effect. This work paves an easy way to construct fully reversible multi-stimuli responsive fluorescence modulation smart materials.

Fluorescence Regulation and Photoresponsivity in AIEE Supramolecular Gels Based on a Cyanostilbene Modified Benzene-1,3,5-Tricarboxamide Derivative.

Supramolecular interactions play an important role in regulating the optical properties of molecular materials. Different arrangements of identical molecules can afford a more straightforward insight into the contributions of supramolecular interactions. Herein, a novel gelator, BTTPA, composed of a benzene-1,3,5-tricarboxamide (BTA) central unit functionalized with three cyanostilbenes is designed, which forms two kinds of gels in DMSO/water mixtures. Depending on the water volume content, the gels exhibit quite different aggregation-induced emission enhancement (AIEE) properties, with one emitting a green emission (G-gel), and the second emitting a blue emission (B-gel). The main reason for this difference is that water affects H-bonding and π-π interactions, further resulting in disparate packing modes of gelators. In addition, only the G-gel displays gel-to-sol transition accompanied with fluorescence switching according to the trans-cis photoisomerization of cyanostilbene under UV light irradiation. The B-gel does not exhibit any change because of its tight hexagonal packing arrangement. Such packing modes restricted the space in which molecules were located and inhibited the transformation of configuration of cyanostilbene. These phenomena underline the incomparable status of packing modes and molecular configuration in regulating fluorescence properties and photoresponse behavior in organic solid-state luminescent materials.

Fluorescence light-up detection of cyanide in water based on cyclization reaction followed by ESIPT and AIEE.

Schiff base 1 (2,4-di-tert-butyl-6-((2-hydroxyphenyl-imino)-methyl)phenol) containing two hydroxyl groups could undergo an oxidative cyclization reaction and then generate hydroxyphenylbenzoxazole (HBO) 2 when CN- was present as a catalyst. The multistep cyclization reaction was proved by spectroscopy, 1H NMR, 13C NMR and mass spectra. C[double bond, length as m-dash]N isomerization is the predominant decay process of the excited states, so sensor 1 is weakly emissive in solution at ambient temperature. When 1 reacts with CN-, the emission is remarkably enhanced, where 1 is converted to 2. The cyclization product HBO 2 displays bright green luminescence in micellar due to the ESIPT (excited-state intramolecular proton transfer) as well as AIEE (aggregation-induced emission enhancement) effect. The detection limit is 5.92 × 10-7 M, lower than the WHO guideline of CN- in drinking water (1.9 µM). The selective and competitive experiments reveal that sensor 1 shows high sensing selectivity and sensitivity for CN- over other anions. Test papers containing absorbed 1 were prepared and applied for practical application of cyanide detection.

Gelation-driven selection in dynamic covalent C[double bond, length as m-dash]C/C[double bond, length as m-dash]N exchange.

Knoevenagel barbiturate derivatives bearing long alkyl chains were proven to form organogels in suitable solvents based on supramolecular interactions. Their reaction with imines allows for component exchange through C[double bond, length as m-dash]C/C[double bond, length as m-dash]N recombination. The effect of various parameters (solvents, chain length, and temperature) on the C[double bond, length as m-dash]C/C[double bond, length as m-dash]N exchange reaction has been studied. Mixing Knoevenagel compound K and imine I-16 in a 1 : 1 ratio generated a constitutional dynamic library containing the four constituents K, I-16, K'-16, and I'. The reversible exchange reaction was monitored by 1H-NMR, showing marked changes in the fractions of the four constituents on sol-gel interconversion as a function of temperature. The library composition changed from statistical distribution of the four constituents in the sol state to selective amplification of the gel forming K'-16 constituent together with that of its agonist I'. The process amounts to self-organization driven component selection in a constitutional dynamic organogel system undergoing gelation. This process displays up-regulation of the gel-forming constituent by component redistribution through reversible covalent connections.

Single sensor for multiple analytes in different optical channel: Applying for multi-ion response modulation.

A Schiff-base, (2,4-di-tert-butyl-6-((2-hydroxyphenyl-imino)-methyl)phenol) (L), has been improved to function as a simultaneous multi-ion probe in different optical channel. The probe changes from colorless to orangish upon being deprotonated by F-, while the presence of Al3+ significantly enhances the fluorescence of the probe due to the inhibition of CN isomerization, cation-induced inhibition of excited-state intramolecular proton transfer (ESIPT), and chelation enhanced fluorescence (CHEF). Dual-channel "off-on" switching behavior resulted from the sequential input of F- and Al3+, reflecting the balance of independent reactions of Al3+ and F- with L and with one another. This sensing phenomenon realizes transformation between multiple states and beautifully mimics a "Write-Read-Erase-Read" logic circuit with two feedback loops.