Aggregation-induced Emission Enhancement Characteristics Research Articles

Tetraphenylethylene fused pyrrolo[3,2-b]pyrrole derivatives with reversible mechanofluorochromic and aggregation-induced emission enhancement characteristics

Modification on typical of molecular unit with aggregation-induced emission (AIE)/aggregation-induced emission enhancement (AIEE) can play a important role in obtaining solid-state fluorescence materials and mechanofluorochromic (MFC) materials. We utilize the multicomponent reaction of TPE-containing aldehyde, arylamine and butane-2,3-dione in the presence of iron(III) perchlorate to design and synthesize two novel MFC materials by combination of the tetraphenylethylene (TPE) and pyrrolo [3,2-b]pyrrole core units. Investigation of CHW-1 and CHW-2 aggregation-induced emission behaviors indicated that these materials all exhibited AIEE properties. Subsequent mechanochromic luminescence tests exhibited reversible mechanochromism natures that involve fluorescent color change from green to yellow (Grinding-induced spectral shift (△λ): 35 nm and 38 nm, respectively). Then the datas (including SEM, PXRD and DSC) revealed that this mechanofluorochromism was ascribed to the transformation of crystal state to the amorphous form. Moreover, CHW-1 and CHW-2 could be applied for optical recording devices and security printing.

Nobiletin with AIEE Characteristics for Targeting Mitochondria and Real-Time Dynamic Tracking in Zebrafish.

Nobiletin is a natural product with multiple physiological activities and is the main ingredient of Pericarpium Citri Reticulatae. We successfully discovered that nobiletin exhibits aggregation induced emission enhancement (AIEE) properties and it has significant advantages such as a large Stokes shift, good stability and excellent biocompatibility. The increase in methoxy groups endows nobiletin a greater fat-solubility, bioavailability and transport rate than the corresponding unmethoxylated flavones. Ulteriorly, cells and zebrafish were used to explore the application of nobiletin in biological imaging. It emits fluorescence in cells and is specifically targeted at mitochondria. Moreover, it has a noteworthy affinity for the digestive system and liver of zebrafish. Due to the unique AIEE phenomenon and stable optical properties of nobiletin, it paves the way for discovering, modifying and synthesizing more molecules with AIEE characteristics. Furthermore, it has a great prospect with regard to imaging cells and cellular substructures, such as mitochondria, which play crucial roles in cell metabolism and death. Indeed, three-dimensional real-time imaging in zebrafish provides a dynamic and visual tool for studying the absorption, distribution, metabolism and excretion of drugs. In this article, more directions and inspiration can be presented for the exploration of non-invasive pharmacokinetic research and intuitive drug pathways or mechanisms.

Naturally Occurring Chalcones with Aggregation-Induced Emission Enhancement Characteristics.

In this paper, the natural chalcones: 2'-hydroxy-4,4',6'-trimethoxychalcone (HCH), cardamonin (CA), xanthohumol (XN), isobavachalcone (IBC) and licochalcone A (LIC) are studied using spectroscopic techniques such as UV-vis, fluorescence spectroscopy, scanning electron microscopy (SEM) and single-crystal X-ray diffraction (XRD). For the first time, the spectroscopic and structural features of naturally occurring chalcones with varying numbers and positions of hydroxyl groups in rings A and B were investigated to prove the presence of the aggregation-induced emission enhancement (AIEE) effect. The fluorescence studies were carried out in the aggregate form in a solution and in a solid state. As to the results of spectroscopic analyses conducted in the solvent media, the selected mixtures (CH3OH:H2O and CH3OH:ethylene glycol), as well as the fluorescence quantum yield (ϕF) and SEM, confirmed that two of the tested chalcones (CA and HCH) exhibited effective AIEE behaviour. On the other hand, LIC showed a large fluorescence quantum yield and Stokes shift in the polar solvents and in the solid state. Moreover, all studied compounds were tested for their promising antioxidant activities via the utilisation of 1,1- diphenyl-2-picrylhydrazyl as a free-radical scavenging reagent as well as potential anti-neurodegenerative agents via their ability to act as acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) inhibitors. Finally, the results demonstrated that licochalcone A, with the most desirable emission properties, showed the most effective antioxidant (DPPH IC50 29%) and neuroprotective properties (AChE IC50 23.41 ± 0.02 μM, BuChE IC50 42.28 ± 0.06 μM). The substitution pattern and the biological assay findings establish some relation between photophysical properties and biological activity that might apply in designing AIEE molecules with the specified characteristics for biological application.

A water-stable Schiff base fluorophore: AIEE behavior, reversible mechanofluorochromism, detection of water content and viscosity of automobile brake fluid, and cell imaging

Imine compounds (Schiff base) have been reported with aggregation-induced emission (AIE)/aggregation-induced emission enhancement (AIEE) characteristics: they were weakly or non-emissive when dissolved well in organic solvents while the fluorescence emission turned on drastically in the presence of water. However, for some of the Schiff bases, the enhanced emission upon aggregation is derived from their parent aldehydes rather than the Schiff base molecule themselves due to the hydrolysis. The susceptibility to hydrolysis has thus limited the wide application of Schiff bases in aqueous media. In this work, a water-stable Schiff base fluorophore DBSFCN was synthesized in which the triphenylamine (TPA) electron donor and benzonitrile electron acceptor were joined together by the imine structure. The hydrolytic stability of DBSFCN was confirmed by structural and spectral analysis. Meanwhile, DBSFCN displayed significant fluorescence emission enhancement in a water/tetrahydrofuran (THF) mixture with high water content and relatively good fluorescence quantum yield at the solid state (0.48), which exhibited a typical AIEE feature. Based on the water stability and AIEE characteristic of DBSFCN, a quantitative method for the determination of water content and kinematic viscosity of the automobile brake fluid was established. In addition, DBSFCN was available in living cell imaging and reversible mechanofluorochromism.

Flexible HSA-interactive phenolphthalein based probe proficient at selective turn-on sensing for Zn2+ & Al3+

A phenolphthalein based fluorescent probe, 3, 3-Bis-[4-hydroxy-3-(pyridine-2-yliminomethyl)-phenyl]-3H-isobenzofu ran-1-one (PHPA), has been synthesized. It exhibits high sensitivity and selectivity towards Zn2+ and Al3+over other relevant water soluble metal ions and also display novel aggregation-induced emission enhancement (AIEE) characteristics. Both complexes followed 2:1 metal to ligand stoichiometry calculated from Job's plot. A significant fluorescence enhancement with a turn-on ratio of ∼94-fold was triggered via chelation-enhanced fluorescence through sensor complex (Zn2+-PHPA) and∼245-fold increase for sensor complex Al3+-PHPA. In addition, the binding sites of both sensor complexes (PHPA-Zn2+ & PHPA-Al3+) have been confirmed through 1H NMR, 13C NMR, FT-IR and ESI-MS spectroscopy. The detection limits is found to be 8.5 × 10−8 M for complex PHPA-Zn2+ and 1.88 × 10−7 M for complex PHPA-Al3+, respectively. The reversible detection of Zn2+ and Al3+ complexes in methanol are also ascertained in the presence of Na2EDTA, enabling the construction of a molecular Logic gate. An advanced-level NOT-AND-OR logic gate has been constructed from a different chemical combinational input and emission output. Human serum albumin (HSA) binding studies were performed by various spectroscopic methods to expound possible bioactivity of PHPA. Interestingly; the AIEE properties of PHPA may advance its impact as studied in methanol-water mixtures with high water contents. To gain the knowledge into the AIEE mechanism of the PHPA, the size and growth process of particles in different volume percentage of water and methanol mixture were studied using time-resolved photoluminescence, dynamic light scattering, and optical microscopic image. The probe PHPA has also been used to detect intracellular Zn2+ ion in A549 cells.

Janus-Type AIE Fluorophores: Synthesis and Properties of π-Extended Coumarin-Bearing Triskelions.

Janus-type triskelion-shaped fluorophores comprising coumarins bearing various electron-donating substituents (1aad, 1add, 1ccd, and 1cdd) were successfully synthesized via an intramolecular Ullmann coupling. Density functional theory (DFT) calculations indicated that all the compounds presented two different molecular surfaces, similar to Janus-type molecules. The absorption and fluorescence spectra of asymmetrical derivatives 1aad, 1add, 1ccd, and 1cdd exhibited a bathochromic shift due to their narrow highest occupied molecular orbital (HOMO) -lowest unoccupied molecular orbital (LUMO) gap. Natural transition orbital (NTO) analysis indicated that the excited state orbital overlaps differ among the C3 symmetrical and asymmetrical dyes. These triskelion-shaped fluorophores were found to form molecular nanoaggregates in THF/H2O mixtures and demonstrated aggregation-induced emission (AIE) enhancement characteristics as a result of restricting their molecular inversion. These results indicate that Janus-type AIE fluorophores are potentially applicable as solid-state fluorescent chiral materials, which can be optimized by controlling their molecular rearrangement in the solid state.

D-A-D type cyclohexyl and cycloheptyl-modified benzo[d]imidazole derivatives with different aggregation-induced emission enhancement (AIEE) and mechanofluorochromic properties

Four tetraphenylethylene or triphenylamine-functionalized donor-acceptor-donor type benzo[d]imidazole derivatives 1–4 with different cycloalkyl substituents were successfully developed and characterized. All of these fluorogenic compounds showed remarkable aggregation-induced emission enhancement characteristics, and these luminogens emitted high brightness orange or green fluorescence in the aggregation state. Furthermore, these cyclohexyl or cycloheptyl-modified benzo[d]imidazole molecules exhibited tunable solid-state fluorescence effect, and their solids demonstrated contrasting mechanically triggered fluorescence responses. More specifically, luminogens 1–3 showed no observable fluorescence changes under mechanical stimulation, while tetraphenylethylene-based cycloheptyl-modified benzo[d]imidazole luminogen 4 displayed reversible mechanochromic fluorescence conversion between green and yellowish-green emission colors. The mechanofluorochromic mechanism of solid 4 was revealed by the powder X-ray diffraction measurements, and the experimental results proved that the phase interconversion between crystalline and amorphous states was responsible for the noticed switchable mechanoresponsive fluorescence. In addition, the mechanical force-sensitive emission of fluorogenic molecule 4 afforded its promising application in ink-free writing.

A novel AIEE active anti-B18H22 derivative-based Cu2+ and Fe3+ fluorescence off-on-off sensor

A novel fluorescence sensor for successive detection of Cu2+ and Fe3+ based on anti-B18H22 derivative which possesses 5-hydroxyisoquinoline as an ionophore was synthesized via a one-pot and its structure and photophysical properties were characterized by NMR, HRMS, FTIR, UV–vis, PL and theoretical calculation. The fluorophore displays two emission peaks at 460 nm and 670 nm in THF solution coming from the emission of the locally excited state and intramolecular charge transfer fluorescence, respectively. The complex exhibited obvious aggregation-induced emission enhancement (AIEE) characteristics in THF/H2O solution by increasing the aqueous concentration from 70% to 95%. The AIEE molecules showed a high selectivity towards Cu2+ over other metal ions by forming a 2:1 metal-to-ligand complex in THF/H2O (fw = 20%) solution, the fluorescence intensity increased as a linear function of the Cu2+ concentration at 460 nm due to the inhibition of PET effect. The fluorescent emission was quenched linearly by the addition of Fe3+, which provides a method for successive determination of Cu2+ and Fe3+ based on ‘off-on-off’ fluorescence of the fluorescent. The detection limit of Cu2+ and Fe3+ was 5.7 × 10−6 M and 7.2 × 10−5 M respectively. Morever, a rapid identification of Cu2+ in the aqueous solution by naked eyes can be realized. In addition, the molecules were pH-sensitive, the fluorescence quenching can be observed in strongly alkaline environment. The method has been applied to the determination of copper ions in water samples with satisfactory results.

A novel optical fiber sensor based on AIEgens for highly selective and sensitive detection of Fe 3+

A novel optical fiber sensor for the detection of Fe3+ based on AIEgens was reported for the first time. A new anti-B18H22 derivative ((5-NH2C9H6N)2B18H20, Referred as to S1) bearing 5-aminoisoquinoline was synthesized via a one-pot and its structure was verified by 1H NMR and HRMS, photophysical properties were characterized by UV–Vis, fluorescence spectrum and theoretical calculation. The fluorophore exhibits obvious aggregation-induced emission enhancement (AIEE) characteristics in THF/H2O solution by increasing the aqueous concentration from 70% to 90%. The aggregation-induced emission (AIE) molecule in THF/H2O (ƒw = 90%) solution shows high selectivity for detecting Fe3+ over other metal ions by forming a 1:1 metal-to-ligand complex, and the detection limit is 5.25 × 10−5 M. The optical fiber sensor based on S1 for the detection of Fe3+ was fabricated, and the detection limit of Fe3+ can reach to be 0.137 nM. The sensor can be used to detect Fe3+ in chemical, environmental and biological fields.

Fluorinated tolane-based fluorophores bearing a branched flexible unit with aggregation-induced emission enhancement characteristics

Precise molecular design of fluorinated tolane-based fluorophores can control both the electron density and molecular aggregated structures.

Dramatically Enhanced and Red-shifted Photoluminescence Achieved by Introducing an Electron-withdrawing Group into a Non-traditional Luminescent Small Organic Compound.

Small organic compounds without any traditional fluorescent chromophores are generally non-emissive, and only very few are reported to emit weak blue fluorescence. Here we synthesized a non-traditional luminescent small organic compound N-(2,2,2-trifluoroethyl)acrylamide (TFAM) with dramatically enhanced and red-shifted photoluminescence by introducing a strong electron-withdrawing group into acrylamide (AM). Very impressively, TFAM emits cyan (472 nm) and yellow-green (560 nm) fluorescence in solutions and solid state, respectively. TFAM also shows aggregation-induced emission enhancement (AIEE) and excitation-dependent fluorescence (EDF) characteristics, as well as temperature and metal cations-responsive fluorescence. Theoretical calculations show that the introduction of electron-withdrawing group leads to a lower energy gap between the HOMO-LUMO energy levels in TFAM than in AM. And strong cooperative hydrogen bonds are formed in TFAM molecules, resulting in rigidification of molecular conformations. The study provides a strategy for preparing non-traditional luminescent compounds with enhanced and red-shifted photoluminescence.

Polymerizable AEE-active Dye with Optical Activity for Fluorescent Nanoparticles Based on Phenothiazine: Synthesis, Self-assembly and Biological Imaging

In consideration of various advantages such as less harmful, higher sensitivity, and deeper imaging depth, etc, AIE materials with long-wave emission are attracting extensive attention in many fields of vascular visualization, organelle imaging, cells tracker, forensic detection, bioprobe and chemosensor, etc. In this paper, a novel fluorescent (R)-PVHMA monomer with chirality and aggregation-induced emission enhancement (AEE) characteristics was acquired through enzymatic transesterification reaction basing on phenothiazine, and its〖 [α]〗_D^(25 ℃) value was about -6.39° with 3.08eV energy level of HOMO and LUMO situations by the quantum calculations. Afterwards, a series of PEG-PVH1 and PEG-PVH2 copolymers with chirality feature were achieved through RAFT polymerization of the obtained (R)-PVHMA and PEGMA with various feed ratios. When the feed molar ratio of (R)-PVHMA increased to 29.6% from 21.5%, its actual molar fractions in the PEG-PVH1 and PEG-PVH2 copolymers accordingly increased to 25.7% from 18.1%. The molecular weight of PEG-PVH1 was about 2.2×104 with narrow PDI, and their kinetics estimation showed a first-order quasilinear procedure. In aqueous solution, the amphiphilic copolymers PEG-PVH could self-assembles into about 100 nm nano-particles. In a 90% water solution of H2O and THF mixture, the fluorescence intensity had the maximum value, and the emission wavelength presented at 580 and 630 nm. The investigation of cytotoxicity and cells uptake showed that PEG-PVH FONs had outstanding biocompatibility and excellent cells absorption effects, which have great potential in bioimaging application.

Chiral Pentaphenylpyrrole Derivatives with Aggregation-Induced Emission Enhancement and Aggregation Induced Circular Dichroism and Their Helical Self-assembly

A pair of enantiomers (S)-P5PdiAM and (R)-P5PdiAM containing two chiral substituents, and their raceme rac-P5PdiAM were synthesized by introducing (R)-/(S)- or racemic 1-phenylethylamine into 1-biphenyl-2,3,4,5-tetraphenylpyrrole. The target compounds all show weak aggregation-induced emission enhancement (AIEE) characteristics in the DMSO/H2O mixed system, indicating that the introduction of chirality hardly affect the photophysical properties of the compound. In addition, the chiral compounds (S)-P5PdiAM and (R)-P5PdiAM show strong circular dichroism (CD) signals in THF/H2O mixed solution with a water fraction of 70%, that is, they exhibit aggregation-induced circular dichroism characteristics (AICD). Because the aggregates of (S)-P5PdiAM and (R)-P5PdiAM emit weakly, there is no circularly polarized luminescence (CPL) signals upon aggregation. The chiral compounds (S)-P5PdiAM and (R)-P5PdiAM can self-assemble to form helical nanofibers in a THF/H2O mixture with a water fraction of 70%, while the racemic rac-P5PdiAM assembled to form nano-particles, indicating that chiral substituents have a great influence on the self-assembly and the morphologies of the nano-aggregates.

Rational design of coumarin fluorophore with solvatochromism, AIE and mechanofluorochromic enhancement properties

A new fluorophore 7-(diphenylamino)coumarin-4-yl pivalate (DPACP) with solvatochromism, aggregation-induced emission (AIE) and mechanofluorochromic (MFC) enhancement characteristics was rationally designed and synthesized by attaching bulky diphenylamine electron-donor and pivalate ester electron-acceptor to coumarin. With solvent polarity increase from n-hexane to acetonitrile, this molecular displayed a bathochromic shift in the emission wavelength (from 436 nm to 553 nm) and a decrease in the quantum yield (from 81.1% to 2.8%), indicating solvatochromic effect. Also, the AIE behaviors were observed in CH3CN/water and THF/water mixture systems. For example, the PL intensity increased 6 times in mixed solvent (CH3CN: water = 10 : 90) compared to that in pure CH3CN. Moreover, the emission of original powder samples was red-shifted (from 438 nm to 483 nm) with fluorescence enhancement (the solid-state quantum yield increase from 19% to 28%) upon grinding, and the emission behaviors of grinding powder samples could be reverted to original state by wetting with n-hexane. Furthermore, the relationship among the molecular structure, intermolecular interactions and emission properties was investigated by single-crystal diffraction analysis. DPACP had a twisted conformation because of steric hindrance from diphenylamine and pivalate ester groups, which played a decisive role in realizing AIE and MFC enhancement behaviors. The absence of π-π stacking observed in single-crystal structure was the main reason for the AIE property. The MFC enhancement property could be ascribed to the disturbance of weak electrostatic interaction of adjacent molecules upon grinding. The bulky group of pivalate ester was first used to construct MFC molecule, and this work provided insights for developing AIE and MFC materials based on conventional planar fluorophore which was always subject to ACQ effect.

Flavanone-Based Fluorophores with Aggregation-Induced Emission Enhancement Characteristics for Mitochondria-Imaging and Zebrafish-Imaging.

Fluorophores with aggregation-induced emission enhancement (AIEE) characteristics applied in bioimaging have attracted more and more attention in recent years. In this work, a series of flavanone compounds with AIEE characteristics was developed and applied to fluorescence imaging of mitochondria and zebrafish. The compounds were readily prepared by the thermal dehydration of chalcone that was obtained by the reaction of o-hydroxyacetophenone and benzaldehyde. Two of these compounds showed significant AIEE characteristics by fluorescence performance experiments, including optical spectra, fluorescence spectra, fluorescence quantum yield (φF), fluorescence lifetime, and scanning electron microscopy (SEM). Compared with traditional organic fluorescent dyes, these compounds have high fluorescence emission and high fluorescence quantum yield in solid or aggregated state, which overcomes the shortcoming of aggregation-caused quenching (ACQ). More importantly, the two compounds exhibited low cytotoxicity and good cytocompatibility in A549 lung cells at the experimental concentration range and they specifically targeted mitochondria, which make it of great potential use in mitochondria labeling. In addition, they were embryonic membrane permeable and had different affinities for different tissues and organs of zebrafish, but mainly distributed in the digestive system, providing a basis for the application of such compounds in bioimaging. These AIEE compounds with superior properties could be of great potential use in mitochondria imaging and other in vivo studies.

Theranostic Nanoparticles with Aggregation-Induced Emission and MRI Contrast Enhancement Characteristics as a Dual-Modal Imaging Platform for Image-Guided Tumor Photodynamic Therapy.

IntroductionAdvanced tumor-targeted theranostic nanoparticles play a key role in tumor diagnosis and treatment research. In this study, we developed a multifunctional theranostic platform based on an amphiphilic hyaluronan/poly-(N-ε-carbobenzyloxy-L-lysine) derivative (HA-g-PZLL), superparamagnetic iron oxide (SPIO) and aggregation-induced emission (AIE) nanoparticles for tumor-targeted magnetic resonance (MR) and fluorescence (FL) dual-modal image-guided photodynamic therapy (PDT).Materials and MethodsThe amphiphilic hyaluronan acid (HA) derivative HA-g-PZLL was synthesized by grafting hydrophobic poly-(N-ε-carbobenzyloxy-L-lysine) (PZLL) blocks onto hyaluronic acid by a click conjugation reaction. The obtained HA-g-PZLLs self-assembled into nanoparticles in the presence of AIE molecules and SPIO nanoparticles to produce tumor-targeted theranostic nanoparticles (SPIO/AIE@HA-g-PZLLs) with MR/FL dual-modal imaging ability. Cellular uptake of the theranostic nanoparticles was traced by confocal laser scanning microscopy (CLSM), flow cytometry and Prussian blue staining. The intracellular reactive oxygen species (ROS) generation characteristics of the theranostic nanoparticles were evaluated with CLSM and flow cytometry. The effect of PDT was evaluated by cytotoxicity assay. The dual-mode imaging ability of the nanoparticles was evaluated by a real-time near-infrared fluorescence imaging system and magnetic resonance imaging scanning.ResultsThe resulting theranostic nanoparticles not only emit red fluorescence for high-quality intracellular tracing but also effectively produce singlet oxygen for photodynamic tumor therapy. In vitro cytotoxicity experiments showed that these theranostic nanoparticles can be efficiently taken up and are mainly present in the cytoplasm of HepG2 cells. After internalization, these theranostic nanoparticles showed serious cytotoxicity to the growth of HepG2 cells after white light irradiation.DiscussionThis work provides a simple method for the preparation of theranostic nanoparticles with AIE characteristics and MR contrast enhancement, and serves as a dual-modal imaging platform for image-guided tumor PDT.

A near-infrared fluorescent probe for ratiometric sensing of SO2 in cells and zebrafish.

Developing suitable molecular tools for monitoring SO2 and its derivatives in living organisms is attractive due to their importance for human health. Herein, the first near-infrared fluorescent probe Mito-HN with aggregation-induced emission enhancement (AIEE) characteristics for ratiometric sensing of SO2 derivatives in vitro, in cells, and in zebrafish was designed and synthesized. By connecting the electron-donating naphthopyran and electron-withdrawing hemicyanine via the alkenyl group, this probe displays a near-infrared fluorescence emission and notable solid-state luminescence with AIEE features. Based on the specific 1,4-addition reaction of HSO3-/SO32- with the C[double bond, length as m-dash]C double bond of Mito-HN, this probe can specifically sense HSO3- in real time with an excellent near-infrared ratiometric fluorescence effect, a low detection limit of 0.17 μM, and a fast response time of less than 30 s. Cell imaging and zebrafish imaging results demonstrate that Mito-HN can ratiometrically not only sense endogenous SO2 derivatives in mitochondria but also monitor SO2 in living organisms. We anticipate that Mito-HN could be applied for the diagnosis of SO2-related diseases in the future.

Self-Assembled Fluorescent Pt(II) Metallacycles as Artificial Light-Harvesting Systems.

Light-harvesting is one of the key steps in photosynthesis, but developing artificial light-harvesting systems (LHSs) with high energy transfer efficiencies has been a challenging task. Here we report fluorescent hexagonal Pt(II) metallacycles as a new platform to fabricate artificial LHSs. The metallacycles (4 and 5) are easily accessible by coordination-driven self-assembly of a triphenylamine-based ditopic ligand 1 with di-platinum acceptors 2 and 3, respectively. They possess good fluorescence properties both in solution and in the solid state. Notably, the metallacycles show aggregation-induced emission enhancement (AIEE) characteristics in a DMSO-H2O solvent system. In the presence of the fluorescent dye Eosin Y (ESY), the emission intensities of the metallacycles decrease but the emission intensity of ESY increases. The absorption spectrum of ESY and the emission spectra of the metallacycles show a considerable overlap, suggesting the possibility of energy transfer from the metallacycles to ESY, with an energy transfer efficiency as high as 65% in the 4a+ESY system.

1,8-Naphthalimide-Based Highly Emissive Luminophors with Various Mechanofluorochromism and Aggregation-Induced Characteristics.

Six 1,8-naphthalimide-based tetraphenylethene derivatives were reported. These highly solid-state emissive compounds showed aggregation-induced emission enhancement or aggregate fluorescence change characteristics. Furthermore, these aggregation-induced green light-emitting or aggregation-induced yellow light-emitting luminophors also exhibited various mechanofluorochromism behaviors involving different fluorescent color changes. To determine the mechanochromic mechanism of these six mechanical stimulus-responsive luminogens, the powder X-ray diffraction (XRD) and X-ray single-crystal measurements were carried out. The powder XRD test results indicated that their interesting mechanofluorochromic behaviors were attributed to the interconversion between crystalline and amorphous states. Meanwhile, the X-ray single-crystal analyses results implied that the twisted molecular conformation and the absence of an intense intermolecular acting force led to a loose packing motif, and the alteration of molecular packing was responsible for the observed mechanofluorochromic effect.

Effect of Substituents on the Photophysical Properties and Bioimaging Application of BODIPY Derivatives with Triphenylamine Substituents.

We investigated the intramolecular charge transfer characteristics in the S1 state of boron-dipyrromethene (BODIPY) derivatives with triphenylamine (TPA) substituents, depending on the substituted position and the number of substituents. Based on the spectroscopic and theoretical results, the β-substitution of TPA on BODIPY hybridizes locally excited and intramolecular charge transfer characteristics in the S1 state because of strong coupling between the highest occupied molecular orbitals of BODIPY and TPA moieties, and consequently, the BODIPY derivatives with β-substituted TPAs exhibit strong red-color fluorescence around 640 nm in nonpolar and moderately polar solvents. The TPA substituent with propeller-like nonplanar geometry could prevent H-type aggregation between neighboring BODIPY derivative units and induce aggregation-induced emission enhancement (AIEE) characteristics of the BODIPY derivatives with TPA substituents, which are helpful to maintain their emission efficiencies under highly concentrated and condensed conditions. Since the red-color emission and AIEE property of the BODIPY derivatives with β-substituted TPAs are promising characteristics for a bioimaging application, we applied these derivatives to L-929 fibroblast cells for cellular imaging. The BODIPY derivative with a single β-substituted TPA (compound 2) was effectively loaded into porous silica nanoparticles (SNPs). Consequently, we achieved good cellular uptake of 2-SNPs and good cellular imaging, which further confirmed the bioimaging ability of 2-SNPs.