Restriction of molecular motion to a higher level: Towards bright AIE dots for biomedical applications

In the late 19th century, scientists began to study the photophysical differences between chromophores in the solution and aggregate states, which breed the recognition of the prototypical processes of aggregation-caused quenching and aggregation-induced emission (AIE). In particular, the conceptual discovery of the AIE phenomenon has spawned the innovation of luminogenic materials with high emission in the aggregate state based on their unique working principle termed the restriction of intramolecular motion. As AIE luminogens have been practically fabricated into AIE dots for bioimaging, further improvement of their brightness is needed although this is technically challenging. In this review, we surveyed the recent advances in strategic molecular engineering of highly emissive AIE dots, including nanoscale crystallization and matrix-assisted rigidification. We hope that this timely summary can deepen the understanding about the root cause of the high emission of AIE dots and provide inspiration to the rational design of functional aggregates.

Reusable Sugar-Based Gelator for Marine Oil-Spill Recovery and Waste Water Treatment

In this work, the gelation ability of a series of novel pyridine-based glucose tailored gelators (DPHAEN, DPHABN, and DPHAHN) with a flexible alkyl chain has been examined in binary solvent mixtures using a number of techniques, for example, UV spectroscopy, FT-IR spectroscopy, NMR spectroscopy, rheology measurement, SEM, XRD, and computational study. Proposed herein is an environment-friendly method to realize toxic dye separation and oil/water separation. It has been found that gels in a selective binary solvent mixture are efficient reusable absorbers of toxic dye molecules. A new gravitational force-driven, simple one-step, toxic dye removal and oil-water separation method is presented for sustainable filtration of waste water and simultaneous collection of oil. The gel column also showed high stability and reusability over repeated use and can be easily scaled for efficient clean-up of a large number of toxic dyes and oil spills present in water. Studies also exposed that the gel column can simultaneously separate dye molecules and mineral oils from water. This simple, green, and efficient method overcomes a nontrivial hurdle for environmentally safe separation of toxic dyes as well as oil/water mixtures and offers insights into the design of advanced materials for practical oil/water separation.

Ultrasound triggered organic mechanoluminescence materials

Ultrasound induced organic mechanoluminescence materials have become one of the focal topics in wireless light sources since they exhibit high spatiotemporal resolution, biocompatibility and excellent tissue penetration depth. These properties promote great potential in ultrahigh sensitive bioimaging with no background noise and noninvasive nanodevices. Recent advances in chemistry, nanotechnology and biomedical research are revolutionizing ultrasound induced organic mechanoluminescence. Herein, we try to summarize some recent researches in ultrasound induced mechanoluminescence that use various materials design strategies based on the molecular conformational changes and cycloreversion reaction. Practical applications, like noninvasive bioimaging and noninvasive optogenetics, are also presented and prospected.

Probing Liquid-Ordered and Disordered Phases in Lipid Model Membranes: A Combined Theoretical and Spectroscopic Study of a Fluorescent Molecular Rotor

An integrated theoretical/experimental strategy has been applied to the study of environmental effects on the spectroscopic parameters of 4-(diphenylamino)phtalonitrile (DPAP), a fluorescent molecular rotor. The computational part starts from the development of an effective force field for the first excited electronic state of DPAP and proceeds through molecular dynamics simulations in solvents of different polarities toward the evaluation of Stokes shifts by quantum mechanics/molecular mechanics (QM/MM) approaches. The trends of the computed results closely parallel the available experimental results thus giving confidence to the interpretation of new experimental studies of the photophysics of DPAP in lipid bilayers. In this context, results show unambiguously that both flexible dihedral angles and global rotations are significantly retarded in a cholesterol/DPPC lipid matrix with respect to the DOPC matrix, thus confirming the sensitivity of DPAP to probe different environments and, therefore, its applicability as a probe for detecting different structures and levels of plasma membrane organization.

Effect of solvation on aggregation-induced luminescence of tetraphenylethene derivatives

The compound TPE-(α-NH2)2 was synthesized. In the water-THF mixture (fw = 90 %), a relatively stable non-emission aggregate with ultrasound-responsive emission property could be obtained.It was found that the preferential...

Aggregation-induced emission (AIE)-guided dynamic assembly for disease imaging and therapy

The phenomenon of aggregation-induced emission (AIE) is inseparable from molecular aggregation and self-assembly. Therefore, the combination of AIE and supramolecular self-assembly is well-matched. AIE-guided dynamic assembly (AGDA) could effectively respond to the endogenous stimuli (such as pH, enzymes, redox molecules) and exogenous stimuli (temperature, light, ultrasound) in the disease microenvironment, so as to achieve specific imaging and diagnosis of the disease lesions. Moreover, AGDA also dynamically adjust the intramolecular motions of AIE molecules, thereby adjusting the energy dissipation pathways and realizing the switch between photodynamic therapy and photothermal therapy for superior therapeutic effects. In this review, we aim to give an overview of the constructing strategies, stimuli-responsive imaging, regulation of intramolecular motion of AGDA in recent years, which is expected to grasp the research status and striving directions of AGDA for imaging and therapy.

Singlet fission in self-assembled PDI nanocrystals

Upon photoexcitation, self-assembled PDI nanocrystals (S1S0) in the form of rods of 70 nm width and 1 μm length are subject to a symmetry breaking charge separation (SBCS) as the first step in the singlet fission (SF) sequence. Hereby, the correlated pair of triplet excited states 1(T1T1) is formed with a quantum yield of 122%. Decoherence and triplet diffusion within the nanocrystals affords a long-lived, uncorrelated pair of triplet excited states (T1 + T1) with a quantum yield of 24%.

General and Scalable Approach to Bright, Stable, and Functional AIE Fluorogen Colloidal Nanocrystals for in Vivo Imaging

Fluorescent nanoparticles built from aggregation-induced emission-active organic molecules (AIE-FONs) have emerged as powerful tools in life science research for in vivo bioimaging of organs, biosensing, and therapy. However, the practical use of such biotracers has been hindered owing to the difficulty of designing bright nanoparticles with controlled dimensions (typically below 200 nm), narrow size dispersity and long shelf stability. In this article, we present a very simple yet effective approach to produce monodisperse sub-200 nm AIE fluorescent organic solid dispersions with excellent redispersibility and colloidal stability in aqueous medium by combination of nanoprecipitation and freeze-drying procedures. By selecting polymer additives that simultaneously act as stabilizers, promoters of amorphous-crystalline transition, and functionalization/cross-linking platforms, we demonstrate a straightforward access to stable nanocrystalline FONs that exhibit significantly higher brightness than their amorphous precursors and constitute efficient probes for in vivo imaging of the normal and tumor vasculature. FONs design principles reported here are universal, applicable to a range of fluorophores with different chemical structures and crystallization abilities, and are suitable for high-throughput production and manufacturing of functional imaging probes.

Computational study of the DPAP molecular rotor in various environments: from force field development to molecular dynamics simulations and spectroscopic calculations

Fluorescent molecular rotors (FMRs) belong to an important class of environment-sensitive dyes capable of acting as nanoprobes in the measurement of viscosity and polarity of their micro-environment. FMRs have found widespread applications in various research fields, ranging from analytical to biochemical sciences, for example in intracellular imaging studies or in volatile organic compound detection. Here, a computational investigation of a recently proposed FMR, namely 4-(diphenylamino)phthalonitrile (DPAP), in various chemical environments is presented. A purposely developed molecular mechanics force field is proposed and then applied to simulate the rotor in a high- and low-polar solvent (i.e., acetonitrile, tetrahydrofuran, o-xylene and cyclohexane), a polymer matrix and a lipid membrane. Subtle effects of the molecular interactions with the embedding medium, the structural fluctuations of the rotor and its rotational dynamics are analyzed in some detail. The results correlate with a previous work, thus supporting the reliability of the model, and provide further insights into the environment-specific properties of the dye. In particular, it is shown how molecular diffusion and rotational correlation times of the FMR are affected by the surrounding medium and how the molecular orientation of the dye becomes anisotropic once immersed in the lipid bilayer. Moreover, a qualitative correlation between the FMR rotational dynamics and the fluorescence lifetime is detected, a result in line with the observed viscosity dependence of its emission. Finally, optical absorption spectra are computed and successfully compared with their experimental counterparts.

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.

The role of Tat peptide self-aggregation in membrane pore stabilization: insights from a computational study

Role of Tat peptide self-aggregation to direct transduction in cells is highlighted in a computational study of dimer versus monomer.

Vapochromic Behaviour of Polycarbonate Films Doped with a Luminescent Molecular Rotor

We report on vapochromic films suitable for detecting volatile organic compounds (VOCs), based on polycarbonate (PC) doped with 4-(triphenylamino)phthalonitrile (TPAP), a fluorescent molecular rotor sensitive to solvent polarity and viscosity. PC films of variable thickness (from 20 up to 80 µm) and containing small amounts of TPAP (0.05 wt.%) were prepared and exposed to a saturated atmosphere of different VOCs. TPAP/PC films showed a gradual decrease and red-shift of the emission during the exposure to solvents with high polarity index and favourable interaction with the polymer matrix such as THF, CHCl3, and acetonitrile. In the case of the most interacting solvents (THF and CHCl3), TPAP/PC films also showed a fluorescence increase at longer exposure times, as a consequence of an irreversible, solvent-induced crystallization process of the polymeric matrix. The vapochromism of TPAP/PC films is rationalized on the basis of alterations of the rotor intramolecular motion upon solvent uptake by PC and polarity effects of the microenvironment. Interestingly, the fluorescence response of the TPAP/PC films shows a non-trivial, tuneable dependence on film thickness during the second solvent-exposure stage. The latter effect is attributed to a variable extent of the crystallization process occurring in the PC films. This observation promptly suggests, in turn, an effective procedure to modulate the spectroscopic response in such functionalized polymeric materials through the precise control of the film thickness.

A near-infrared AIEgen for specific imaging of lipid droplets

A new near-infrared AIE luminogen is developed for specific lipid droplet imaging with high brightness, good biocompatibility and superior photostability.

A novel multi-stimuli responsive gelator based on d-gluconic acetal and its potential applications

The goal of integrating multi-stimuli responsiveness and versatile applications into a single organogelator is achieved.

Interplay Between Mechanochemistry and Sonochemistry

Ultrasonic irradiation-based mechanochemical strategies have recently been the subject of intensive investigation because of the advantages they offer. These include simplicity, energy savings and wide applicability. Traditional areas of sonoprocessing such as cleaning, efficient mixing and solid activation have been extended to both macromolecular and micro/nanostructures, some of which are biologically significant, ultrasound-responsive actuators and crystal design, among others. Unlike conventional mechanochemical protocols, which require little solvent usage if any at all, mechanical (and chemical) effects promoted by ultrasound are observed in a liquid medium. Tensile forces, which share similarities with solid mechanochemistry, are generated by virtue of nonlinear effects, notably cavitation, when high-amplitude waves propagate in a fluid. This work aims to provide insight into some recent developments in the multifaceted field of sono-mechanochemistry using various examples that illustrate the role of ultrasonic activation, which is capable of boosting hitherto sterile transformations and inventing new crafts in applied chemistry. After a preliminary discussion of acoustics, which is intended to provide a mechanistic background, we mainly focus on experimental developments, while we often mention emerging science and occasionally delve into theoretical models and force simulations.