AIE Fluorescent Gelators with Thermo-, Mechano-, and Vapochromic Properties

Aggregation-Induced Emission-Active Nanostructures: Beyond Biomedical Applications

The discovery of aggregation-induced emission (AIE) phenomenon in 2001 has had a significant impact on materials development across different research disciplines. AIE-active materials have been widely exploited for various applications in optoelectronics, sensing, biomedical, and stimuli-responsive systems, etc. This is made possible by integrating AIE features with other fields of science and engineering, such as nanoscience and nanotechnology. AIE has been extensively employed, particularly for biomedical applications, such as biosensing, bioimaging, and theranostics. However, development of AIE-based nanotechnology for other applications is comparatively less, although there have been increasing research activities in recent years. Given the significance and potential of the marriage between AIE hallmark and nanotechnology in AIE-active materials development, this review article summarizes and showcases the latest research efforts in AIE-based nanomaterials, including nanomaterials synthesis and their nonbiomedical applications, such as sensing, optoelectronics, functional coatings, and stimuli-responsive systems. A perspective on the outlook of AIE-based nanostructured materials and relevant nanotechnology for nonbiomedical applications will be provided, giving an insight into how to design AIE-active nanostructures as well as their applications beyond the biomedical domain.

Anti-counterfeiting Behaviour of Organic-Inorganic Hybrid Silica Film with a Chiral Smectic C Structure

Artificial photonic materials based on chiral liquid-crystalline nanostructures have attracted increasing interests for their wide applications as sensors, anti-counterfeit measures, displays and colour filters. Although the structurally coloured films with chiral nematic structures or blue phases have been prepared, the ones fabricated by fixing chiral smectic C (SmC*) phases have been rarely reported. In this work, organic-inorganic hybrid silica (OIHS) films with a SmC* structure were reported for the first time. An organosilane (CSC) with an enantiotropic SmC* phase was synthesized. The OIHS films with a SmC* structure were fabricated by the polycondensation of CSC under an acidic condition. The colour patterns can be observed in the oblique view, but not be observed in the vertical view, which is mainly due to the light scattering of the nanoparticles on film surface and the selective Bragg reflection of film inside. Therefore, such properties make the OIHS films promising candidates for anti-counterfeiting applications.

Configuration-Dependent Liquid Crystal and Gel Behaviors of Tetraphenylethene-Containing Main-Chain Copolyesters

The construction of aggregation-induced emission-active (AIE-active) gelators with liquid crystal properties remains a challenge. Moreover, it is still unclear for the effect of AIE configuration on liquid crystal, gel and AIE behaviors in one system. Herein, two main-chain liquid crystalline copolyester gelators with a single configuration of AIEgen TPE, mesogen biphenyl and pendent amide groups have been synthesized through melt polycondensation. Both copolyesters display smectic phase, while E-P20 possesses a wider temperature range of liquid crystal and a narrower layer distance owing to the more serious nonlinear "defect" of Z-TPE than E-TPE units. In addition, E-P20 and Z-P20 can form AIE-active gels with the minimum gelation concentration (MGC) values of 10 wt% and 4 wt% in ethyl acetate mainly via hydrogen bond between the pendent amide groups, respectively. These AIE-active gels show potential applications in temperature sensor, information storage, and so on. This article is protected by copyright. All rights reserved.

A new aggregation induced emission enhancement (AIEE) dye which self-assembles to panchromatic fluorescent flowers and has application in sensing dichromate ions

We report for the very first time the crystal structure and self-assembly of a new aggregation-induced emission enhancement (AIEE) dye 4-(5-methoxythiazolo[4,5-b]pyridin-2-yl)-N,N-dimethylaniline (TPA) and its application in sensing dichromate ions. TPA reveals cyan blue emission under UV and visible light. The self-assembly properties of TPA were studied extensively by scanning electron microscopy (SEM) which revealed the formation of beautiful flower-like morphologies. These structures revealed both green and red fluorescence under FITC and rhodamine filters respectively when observed through fluorescence microscopy connoting the panchromatic emission properties of TPA from blue to red. The interactions which cause self-assembled structure formation in TPA were also validated theoretically using density functional theory (DFT) calculations. Crystal and molecular structure analysis of TPA was carried out via single-crystal X-ray diffraction to visualize the intermolecular interactions occurring in the solid-state and to study the structure-photophysical property relationship in the aggregated state. The photophysical properties of TPA were also studied extensively by UV-visible and fluorescence spectroscopy and its quantum yield and fluorescence lifetime were calculated by time-correlated single-photon counting (TCSPC). Interestingly, TPA could efficiently sense dichromate (Cr₂O₇^2-) ions in an acidic medium and an interesting morphological transition from a fluorescent flower to non-fluorescent disassembled structures could also be observed. The limit of detection of TPA for Cr₂O₇^2- ions was found to be as low as 5.5 nM, suggesting its exceptional sensitivity. More importantly, TPA could selectively sense Cr₂O₇^2- ions in real water samples even in the presence of other metal ions routinely present in polluted water, hence making it practically useful for water quality monitoring.

Trans/cis-stereoisomers of triterpenoid-substituted tetraphenylethene: aggregation-induced emission, aggregate morphology, and mechano-chromism

Trans/cis stereoisomers with multiple functionalities play an important role in chemistry and materials science. In this work, two pure stereoisomers (trans- and cis-TPE-2GA) of the tetraphenylethene (TPE) derivatives bi-substituted by a bio-resourced rigid triterpenoid and glycyrrhetinic acid (GA) were synthesized and characterized by 1D and 2D NMR, single crystal analysis, and HR-MS. Both trans- and cis-TPE-2GA are thermally stable even on heating at 160 °C for 30 min, whereas they can undergo trans-to-cis and cis-to-trans photoisomerization under similar UV illumination. The introduction of triterpenoid units endowed isomers with different aggregation-induced emission (AIE) and self-assembly properties and distinct crystallinity. Trans- and cis-TPE-2GA exhibit different evolution of the fluorescent intensity in water/acetone mixture with the increase in the water fraction, which are closely related to the different evolution of the aggregate morphology, from nanorods to nanospheres for trans-TPE-2GA, while from twisted ribbons, to nanotubes and nanospheres for cis-TPE-2GA. In the solid state, the mechano-chromic properties are shown by cis-TPE-2GA, while no mechano-chromic effect is observed for trans-TPE-2GA under the same grinding conditions because of their distinct crystallinity. Finally, theoretical calculation and photophysical study demonstrate that despite both isomers being assigned to the charge transfer state emission, cis-TPE-2GA has a slightly lower energy gap, a higher quantum yield, and a longer lifetime in comparison with trans-TPE-2GA, which explained their difference in the fluorescence and mechano-chromic properties. This work may improve the understanding of the TPE-based trans and cis stereoisomers, which will be beneficial in the design of novel TPE-based functional materials.

Luminescent Behavior of Gels and Sols Comprised of Molecular Gelators

We present a brief review of some important conceptual and practical aspects for the design and properties of molecular luminescent gelators and their gels. Topics considered include structural and dynamic aspects of the gels, including factors important to their ability to emit radiation from electronically excited states.

Synthesis of the cationic fluorescent probes for the detection of anionic surfactants by electrostatic self-assembly

Anionic surfactants were widespread used in car cleaning agents, household detergents, agricultural and industrial processes, and considered as a major source of environmental pollutant. Therefore, it is necessary to develop a fast, simple, highly selective and sensitive probe for the detection of anionic surfactants. Here, we synthesized two aggregation induced emission (AIE)-active molecules 4,4',4″,4‴-(ethene-1,1,2,2-tetrayltetrakis(benzene-4,1-diyl))tetrakis (1-(4-bromobenzyl)pyridin-1-ium) bromide (TPE-Br) and 4,4',4″,4‴-(ethene-1,1,2,2-trayltetrakis(benzene-4,1-diyl))tetrakis(1-methylpyridin-1-ium)iodide (TPE-I), which were then applied as fluorescence probes for detecting sodium dodecyl sulfate (SDS) with high selectivity and sensitivity. In the presence of SDS, a multi-fold fluorescence emission intensity enhancement was observed in both two probes (TPE-Br and TPE-I) due to the electrostatic self-assembly of AIE molecular. The limits of detection are 71.5 and 120 nM for TPE-Br and TPE-I, respectively. This study may provide a new strategy for environmental monitoring by AIE-based fluorescent probe.

CO2 -Activated Reversible Transition between Polymersomes and Micelles with AIE Fluorescence

Fluorescent polymersomes with both aggregation-induced emission (AIE) and CO₂ -responsive properties were developed from amphiphilic block copolymer PEG-b-P(DEAEMA-co-TPEMA) in which the hydrophobic block was a copolymer made of tetraphenylethene functionalized methacrylate (TPEMA) and 2-(diethylamino)ethyl methacrylate (DEAEMA) with unspecified sequence arrangement. Four block copolymers with different DEAEMA/TPEMA and hydrophilic/hydrophobic ratios were synthesized, and bright AIE polymersomes were prepared by nanoprecipitation in THF/water and dioxane/water systems. Polymersomes of PEG₄₅ -b-P(DEAEMA₃₆ -co-TPEMA₆ ) were chosen to study the CO₂ -responsive property. Upon CO₂ bubbling vesicles transformed to small spherical micelles, and upon Ar bubbling micelles returned to vesicles with the presence of a few intermediate morphologies. These polymersomes might have promising applications as sensors, nanoreactors, or controlled release systems.