Polyhalogenated aminobenzonitriles vs. their co-crystals with 18-crown-6: amino group position as a tool to control crystal packing and solid-state fluorescence

Strengthening (para-isomers) or weakening (ortho-isomers) of π-electron aggregation due to the crystal structure rearrangement results in the bathochromic or hypsochromic shift of the fluorescence maximum.

Aggregation-Induced Emission Fluorescent Gels: Current Trends and Future Perspectives

The development of fluorescent gels, if not the current focus, is at the center of recent efforts devoted to the invention of a new generation of gels. Fluorescent gels have numerous properties that are intrinsic to the gel structure, with additional light-emitting properties making them attractive for different applications. This review focuses on current studies associated with the development of fluorescent gels using aggregation-induced emission fluorophores (AIEgens) to ultimately suggest new directions for future research. Here, we discuss major drawbacks of the methodologies used frequently for the fabrication of fluorescent gels using traditional fluorophores compared to those using AIEgens. The fabrication strategies to develop AIE-based fluorescent gels, including physical mixing, soaking, self-assembly, noncovalent interactions, and permanent chemical reactions, are discussed thoroughly. New and recent findings on developing AIE-active gels are explained. Specifically, physically prepared AIE-based gels including supramolecular, ionic, and chemically prepared AIE-based gels are discussed. In addition, the intrinsic fluorescent properties of natural gels, known as clustering-triggered fluorescent gel, and new and recent relevant findings published in peer-reviewed journals are explained. This review also revealed the biomedical applications of AIE-based fluorescent hydrogels including drug delivery, biosensors, bioimaging, and tissue engineering. In conclusion, the current research situation and future directions are identified.

Co-crystals of polyhalogenated diaminobenzonitriles with 18-crown-6: effect of fluorine on the stoichiometry and supramolecular structure

Fluorine in the ortho-position of diaminobenzonitrile promotes the formation of the N–H⋯NC bond which results in a 3D supramolecular structure of the co-crystal.

Ultralow-Molecular-Weight Stimuli-Responsive and Multifunctional Supramolecular Gels Based on Monomers and Trimers of Hydrazides

The simpler, the better. A series of simple, neutral and ultralow-molecular-weight (MW: 140-200) hydrazide-derived supramolecular gelators have been designed and synthesized in two straightforward steps. For non-conjugated cyclohexane-derived hydrazides, their monomers can self-assemble to form gels through intermolecular hydrogen bonds and dipole-dipole interactions. Significantly, conjugated phthalhydrazide can self-aggregate into planar and circular trimers through intermolecular hydrogen bonds and then self-assemble to form gels through intermolecular π-π stacking interactions. It is interesting that these simple gelators exhibit unusual properties, such as self-healing, multi-response fluorescence, and visual and selective recognition of chiral (R)/(S)-1,1'-binaphthalene-2,2'-diamine and S^2- through much different times of gel re-formation and blue-green color change, respectively. These results underline the importance of supramolecular gels and extend the scope of supramolecular gelators.

Insights into the aggregation-induced emission of 1,8-naphthalimide-based supramolecular hydrogels

The study of aggregation-induced emission (AIE) of a series of 1,8-naphthalimide derivatives in aqueous media is reported herein. Some of these molecules constitute the first examples of 1,8-naphthalimide-containing amino acid derivatives that form hydrogels with excellent photophysical and mechanical properties. The present study provides further insights for the rational design of water-compatible stimuli-responsive photonic materials presenting AIE. AIE was quantitatively evaluated by measuring the fluorescence quantum yields of the molecules. Gelators 1 and 2 exhibit self-assembled fibrillar morphologies and present the best performance regarding the AIE effect, showing a remarkable enhancement in fluorescence intensity of 4700% and reaching a notable fluorescence quantum yield (Φf) of 30%. Non-gelator molecules 6 and 7 form nanoparticles, which also present AIE, but with emissions corresponding to their excimers. Therefore, the AIE intensity and wavelength are regulated by the type of aggregate morphology: fibers, nanoparticles or soluble species.

Self-Assembled α-Cyanostilbenes for Advanced Functional Materials

In the specific context of condensed media, the significant and increasing recent interest in the α-cyanostilbene (CS) motif [ArCHC(CN)Ar] is relevant. These compounds have shown remarkable optical features in addition to interesting electrical properties, and hence they are recognized as very suitable and versatile options for the development of functional materials. This progress report is focused on current and future use of CS structures and molecular assemblies with the aim of exploring and developing for the next generations of functional materials. A critical selection of illustrative materials that contain the CS motif, including relevant subfamilies such as the dicyanodistyrylbenzene and 2,3,3-triphenylacrylonitrile shows how, driven by the self-assembly of CS blocks, a variety of properties, effects, and possibilities for practical applications can be offered to the scientific community, through different rational routes for the elaboration of advanced materials. A survey is provided on the research efforts directed toward promoting the self-assembly of the solid state (polycrystalline solids, thin films, and single crystals), liquid crystals, nanostructures, and gels with multistimuli responsiveness, and applications for sensors, organic light-emitting diodes, organic field effect transistors, organic lasers, solar cells, or bioimaging purposes.

Bright conjugated polymer nanoparticles containing a biodegradable shell produced at high yields and with tuneable optical properties by a scalable microfluidic device

This study compares the performance of a microfluidic technique and a conventional bulk method to manufacture conjugated polymer nanoparticles (CPNs) embedded within a biodegradable poly(ethylene glycol) methyl ether-block-poly(lactide-co-glycolide) (PEG_5K-PLGA_55K) matrix. The influence of PEG_5K-PLGA_55K and conjugated polymers cyano-substituted poly(p-phenylene vinylene) (CN-PPV) and poly(9,9-dioctylfluorene-2,1,3-benzothiadiazole) (F8BT) on the physicochemical properties of the CPNs was also evaluated. Both techniques enabled CPN production with high end product yields (∼70-95%). However, while the bulk technique (solvent displacement) under optimal conditions generated small nanoparticles (∼70-100 nm) with similar optical properties (quantum yields ∼35%), the microfluidic approach produced larger CPNs (140-260 nm) with significantly superior quantum yields (49-55%) and tailored emission spectra. CPNs containing CN-PPV showed smaller size distributions and tuneable emission spectra compared to F8BT systems prepared under the same conditions. The presence of PEG_5K-PLGA_55K did not affect the size or optical properties of the CPNs and provided a neutral net electric charge as is often required for biomedical applications. The microfluidics flow-based device was successfully used for the continuous preparation of CPNs over a 24 hour period. On the basis of the results presented here, it can be concluded that the microfluidic device used in this study can be used to optimize the production of bright CPNs with tailored properties with good reproducibility.

Carbazole modified salicylaldimines and their difluoroboron complexes: effect of the tert-butyl and trifluoromethyl terminal groups on organogelation and piezofluorochromism

Luminescent nanofibers were generated from nontraditional π-gelators based on salicylaldimines and their difluoroboron complex bearing tert-butyl carbazole and trifluoromethylbenzene.

Color-Tunable Cyano-Substituted Divinylene Arene Luminogens as Fluorescent π-Gelators

The synthesis of three cyano-substituted divinylene π-gelators is reported. The modulation of the color is achieved by placing the cyano groups in appropriate position of the conjugated backbone, thus modulating the donor-acceptor interaction. Variable-temperature UV-vis data have been utilized to investigate the self-assembly of the gelators 1-3 that is governed by a cooperative mechanism. A complete set of photophysical parameters (ΦF,τ, kr and knr) demonstrate the role of the molecular aggregation in enhanced emission upon self-assembly.

Enhanced room-temperature phosphorescence of triphenylphosphine derivatives without metal and heavy atoms in their crystal phase

Two simple triphenylphosphine derivatives have weak phosphorescence in solution, but the emissions were enhanced by 6.5 and 27 times, respectively, in crystals.

Recent emergence of photon upconversion based on triplet energy migration in molecular assemblies

This Feature Article reviews an emerging field of triplet energy migration-based photon upconversion (TEM-UC) that allows highly efficient photon upconversion at low excitation power.

An efficient phase-selective gelator for aromatic solvents recovery based on a cyanostilbene amide derivative

Two novel low molecular weight organogelators (LMOGs) 1 and 2 composed of a cholesteryl group, an amide group and various terminal cyanostilbene moieties were synthesized. They could form stable gels in p-xylene. In particular, 2 with more extended π-conjugation length showed remarkable gelation ability in many aromatic solvents, chloroform and chloroform-containing mixed solvents at a relatively low concentration. FT-IR and XRD spectra indicated that the difference between 1 and 2 in the gelation properties may result from the deviation of the intermolecular hydrogen bonding and π–π stacking as driving forces for the formation of the gels. Significantly, 2 can function as an efficient room-temperature phase-selective gelator (PSG) for potential application in the separation and recovery of various aromatic solvents from its mixture with water. Meanwhile, the gelator can be easily recovered and reused several times. Furthermore, the phase-selective gelation properties of 2 can provide a simple and feasible approach for the removal of the rhodamine B (RhB) dye from water.

Bent-core liquid crystalline cyanostilbenes: fluorescence switching and thermochromism

Incorporation of the cyanostilbene unit in a bent-core liquid crystal-type structure gives rise to fluorescent systems whose emission is very sensitive to different environments.

Organogels formed by substituent-free pyrene-appended oligo(m-phenylene ethynylene)s

Substituent-free pyrene-appended m-phenylene ethynylene oligomers have been revealed to gelate organic solvents of low and modest polarity.

Emission enhanced two-component gels for the detection of organic amine vapors

A two-component gelator with enhanced emission could be used to quantitatively detect and discriminate between aliphatic and aromatic organic amine vapors.

Reversible thermochromic polymer film embedded with fluorescent organogel nanofibers

We report a reversible thermochromic nanocomposite polymer film composed of fluorescent organogel fibers and a highly cross-linked polymer matrix. A series of cyano-substituted oligo(p-phenylenevinylene) (CN-OPV) derivatives were synthesized by the reaction of dialdehydes with phenyl or naphthyl acetonitrile under basic conditions. Among the CN-OPV derivatives, NA-DBA having naphtyl moieties and dodecyloxy chains formed a stable organogel in a cross-linkable monomeric solvent (ethylene glycol dimethacrylate). The organogel showed a thermoreversible sol-gel transition, accompanying the emission color change. A nanocomposite polymer film obtained by photopolymerization of the organogel between two quartz plates also exhibited reversible thermochromism. Under 365 nm irradiation, the orange color of the film at 25 °C became yellowish green at 120 °C. The fluorescence spectroscopy, DSC, and microscopy results determined that the thermally reversible self-assembly of NA-DBA occurred in the polymer matrix, resulting in reversible thermochromism. The melted gelator molecules at 120 °C did not diffuse into the polymer matrix probably because of poor interactions of the gelator molecules with the polymer matrix. The NA-DBA molecules dispersed in poly(methyl methacrylate), without forming a supramolecular structure, did not show thermochromism.

Self-assembly of azobenzene-based two-component gels

Two-component gels were formed and their photophysical properties were dependent on the ratio of the two compounds.