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In this work, a new kind of butterfly-like molecules of oxacalix[2]arene[2]pyrazine (OAP) are reported, which exhibit typical characteristics of aggregation-induced emission (AIE) via the restriction of intramolecular vibration (RIV) mechanism. Unlike any of the reported RIV-type AIE molecules, the synthetic procedures of which are complicated and associated high costs, OAP AIEgens can be synthesized in a facile manner by a one-step catalyst-free reaction using commercially available materials. Notably, OAP AIEgens are ideal ligands for constructing metal-organic frameworks (MOFs) due to their built-in coordination sites of pyrazine groups. OAP-based MOFs exhibit multiple potential applications in reversible gas response, encrypted information storage, and construction of white light-emitting devices. This work enriches limited kinds of RIV-type AIEgens, offers additional selections of bridging ligands for constructing luminescent MOFs and provides a visualized prototype to understand the effect of RIV process on the luminescence property of MOFs.

Fluoran salicylaldehyde hydrazone metal complex(FSHMC) is a kind of recently reported photo-responsive system, which has the advantages of simple synthesis, multiple colors as well as distinct color change before and after UV light irradiation. However, the emission property of FSHMC is relatively unitary. In solid state, especially, only fluorescence quench is induced after UV light irradiation, which limits their applications. In this work, a typical aggregation-induced emission(AIE) moiety of tetraphenylethene(TPE) was introduced to the design of FSHMC. The obtained FSHMC, 2-Zn, exhibited reversible color and fluorescence changes upon UV light irradiation. Due to the AIE feature of compound 2, 2-Zn exhibited different emission changes upon UV light irradiation in THF and in solid matrix, because of the fluorescence resonance energy transfer(FRET) process from TPE moiety to rhodamine B moiety.

Silver clusters usually have intriguing aesthetic structures and multiple application prospects in optical materials, chemocatalysis, bioimaging and chemosensors. However, these practical applications usually suffer from the instability of silver clusters. How to transform this disadvantage into an advantage for meaningful applications of silver clusters remains challenging. In this work, we judiciously prepared a silver cluster of Ag24 using an aggregation-induced emission (AIE) ligand. Due to the argyrophilia of sulfur, Ag24 can be easily destroyed by sulfur-containing pesticides such as ethion, releasing the AIE fragments. As a result, a “turn-on” emission change was observed, making Ag24 a potential chemosensor for detecting ethion in water dominated solutions. This work provides new thoughts for the design of silver cluster-based luminescent chemosensors, and broadens the application range of silver clusters.

As a potential photochromic system, acylhydrazones exhibit many outstanding advantages including low cost, simple synthesis and high modifiability compared with some classic photochromic systems. However, the absorption wavelengths of acylhydrazones usually locate in ultraviolet region, which makes the band separation between the absorbance maxima of its irradiated and unirradiated forms cannot be observed by naked eyes and greatly limits their practical applications. In this work, a simple strategy for constructing acylhydrazone photochromic system with visible color/emission change is provided. Rhodamine 6G hydrazine-2-aldehyde-pyridine Schiff base (compound 3) is designed and synthesized by combining acylhydrazone with Rhodamine 6G structure. The introduction of Rhodamine 6G moiety to 3 not only makes it remain all the advantages of acylhydrazone photochromic system but also exhibits visible photo-induced color/emission changes both in solution and in a solid matrix. Moreover, 3 exhibits reversible photochromic property with good fatigue resistance, which makes it an excellent candidate for photo-patterning.

Twisted intramolecular charge transfer (TICT) process endow the luminogens containing rotatable electron donor-π-acceptor (D-π-A) structure with abundant electronically excited states, resulting in multiple photophysical properties. In this work, a new propeller-like molecule of 5,6-di(4-N,N-(dimethylamino)phenyl)pyrido[2,3-b]pyrazine (APPP) with rotatable D-π-A structure was facilely prepared, which exhibited typical TICT character. Interestingly, aggregation/viscosity-induced emission and third-order nonlinear optical (NLO) signal inversion from reverse saturation absorption to saturation absorption in aggregated state or solutions with high viscosity were observed in this system. Mechanism study showed that these properties were originated from the restricted intramolecular rotation (RIR) process, which not only cut off the non-radiative transition channel of excited electron but also influenced the excited electron transition rate from charge transfer (CT) state to TICT state. According to these results, a temperature-triggered third-order NLO optical switch was successfully designed. This work affords a new type of aggregation-induced emission luminogen (AIEgen) with third-order NLO properties, and more importantly, provides a visualized prototype to understand the origination of third-order NLO properties in TICT systems.

A propeller-like pyrene derivative of diphenyl-1-pyrenylphosphine (DPPP) is designed and synthesized. DPPP exhibits a unique photo-triggered AIE/ACQ transition with a remarkable third-order nonlinear optical signal change, which is proved to originate from the photo-induced oxidation of a phosphorus atom.

Aggregation-induced emission luminogens (AIEgens) with a large electron donor and acceptor (D-A) conjugated system have been widely used in the development of organic light emitting diodes (OLEDs), chemosensors, and bioimaging materials due to their excellent properties such as high quantum yields, long emission wavelengths, controllable luminescence lifetimes, and nonlinear optics (NLO) properties. However, most of the AIE materials have been derived from limited classic AIE cores such as tetraphenylethene (TPE) and tetraphenylpyrazine (TPP), and thus, tedious syntheses or later modifications toward those AIEgens have always been unavoidable. In this report, a type of atypical AIEgens (designated as ASIQs) composed of large conjugated structures with a natural electron D-A system is disclosed, which shows large Stokes shifts, high photostabilities, excellent cell permeabilities, low biotoxicities, and good two-photon excited capacities, making them suitable for applications of one-photon/two-photon targeted imaging in live cells. In short, this work offers a type of atypical AIEgens which will possibly become an ideal platform leading to more structurally diverse and functionally excellent AIE-based luminescent materials.

Metal clusters are useful phosphors, but highly luminescent examples are quite rare. Usually, the phosphorescence of metal clusters is hindered by ambient O2 molecules. Transforming this disadvantage into an advantage for meaningful applications of metal clusters presents a formidable challenge. In this work, we used ligand engineering to judiciously prepare colour-tuneable and brightly emitting Cu(I) clusters that are ultrasensitive to O2 upon dispersion in a fluid solution or in a solid matrix. When the O2 scavenger dimethyl sulfoxide (DMSO) was used as the solvent, joint photo- and oxygen-controlled multicolour switches were achieved for the first time for metal cluster-based photopatterning and photo-anticounterfeiting. More importantly, an aggregation-induced barrier to oxygen, a new aggregation-induced emission mechanism for metal clusters, was proposed, providing a new pathway to realizing the intense emission of metal clusters in the aggregated state. These results are expected to promote the application of metal clusters and enrich the luminescence theory of metal cluster aggregates.

Aggregation-induced emission luminogens (AIEgens) have been widely used in the development of functional materials due to their excellent luminescence properties in the solid state. The development of new AIEgens is of great significance. In this work, a novel o-phthalimide-based AIEgen of 2,3-diphenylquinoxaline-6,7-dicarboimide (2) is reported, which exhibited multifunctional sensing applications. Interestingly, compound 2 exhibited ultrafast photo-response properties upon UV light irradiation in both the dissolved state and solid state, which was attributed to a unique photo-induced rearrangement reaction. This property of 2 makes it suitable for UV sensing and photo-patterning materials with a significant fluorescence change. Meanwhile, based on the highly specific interaction between Hg(II) and the o-phthalimide moiety of 2, a complex of 2-Hg-2 formed in the presence of 0.5 equiv. Hg(II), resulting in a strong fluorescence change of 2. The active hydrogen in the o-phthalimide moiety also makes the fluorescence of 2 sensitive to the pH of aqueous solutions. Due to these characteristics, 2 was successfully used in the detection of UV light, Hg(II) and the pH of aqueous solutions, in which 2 exhibited satisfactory detection performance.

The real-time monitoring of spontaneous molecular directed motion is a highly important but very challenging task. In this work, a rod-like aggregation-induced emission (AIE) molecule was carefully designed and facilely synthesized. The AIE molecule, the salicylaldehyde 4-butoxyaniline Schiff base (SBA), exhibited a unique self-recovery property from a semi-ordered structure to an ordered structure along with significant fluorescence changes after grinding. The fluorescence changes were monitored to obtain important kinetic information regarding the spontaneous molecular directed motion process, including the kinetic order, rate constants, half-life, and apparent activation energy. Unlike instrumental analytical methods such as PXRD and AFM, which only give information on a stable state of samples, the proposed fluorescence method provides a new perspective for real-time visualization of spontaneous molecular directed motion in situ in the solid state.

Photo-induced free radical production was observed in tetraphenylethylene ligand-based metal-organic frameworks (MOFs). This feature endows the MOFs with reversible, fast, obvious, and controllable photo-induced color/emission transformation, excellent fatigue resistance ability and good light stability.

Photo-responsive materials with tunable properties by multiple stimuli have been widely used as molecular machines, molecular logic gates, optical data storages, etc. In this work, we report a rhodamine B-based photo-responsive system, whose properties could be facilely modulated by metal ions (Zn(II), Ni(II) and Hg(II)). These metal ions endow the complexes (L-Zn, L-Ni and L-Hg) with similar photochromic property but distinctly different photo-induced fluorescence change. Upon UV light irradiation, the spirolactam ring in rhodamine B moiety turned from a close form to an open form, along with enlarged conjugated structure with intense absorbance. Interestingly, fluorescence “turn off”, “no change” and “turn on” responses were induced by Zn(II), Ni(II) and Hg(II) respectively upon UV light irradiation. Taking advantage of the prominently different characteristics caused by metal ions, different logic gates were designed by simply varying the inputs of metal ions and UV light. This work provided a new strategy for developing multifunctional photo-responsive materials, which were further beneficial for constructing photo-controlled logic gates with tunable performance.

The real-time monitoring of spontaneous molecular directed motion is a highly important but very challenging task. In this work, a rod-like aggregation-induced emission (AIE) molecule of salicylaldehyde 4-butoxyaniline Schiff base (SBA) was deliberately designed and facilely synthesized, which exhibits unique self-recovery property from semi-ordered structure to ordered structure alongwith significant fluorescence change after grinding. The monitoring of the fluorescence change provides rich kinetic information including kinetic order, rate constants, half-life and apparent activation energy of the spontaneous molecular directed motion process. Unlike instrumental analytical methods such as PXRD and AFM, which only give the information of a stable state of samples, the fluorescence method provided a new perspective to real-time visualize spontaneous molecular directed motion in situ in solid state.

Using an aggregation-induced emission luminogen (AIEgen) as the fluorescence signal part, a novel molecularly imprinted polymers (MIPs) based ratiometric fluorescence sensor (AIE-MIPs-1) was developed for detecting Rhodamine 6G (Rh6G) in food samples including dried papaya and beverage. The sensor exhibited strong blue fluorescence itself at 420 nm. Upon the adsorption of Rh6G, the original fluorescence intensity decreased while a new fluorescence emission peak at 562 nm increased gradually, which showed typical ratiometric fluorescence change. Good linear relationship between the fluorescence intensity ratio (I562/I420) and the concentration of Rh6G was obtained in the range of 0.0–10.0 μmol/L. A detection limit of 0.26 μmol/L Rh6G was achieved. Moreover, AIE-MIPs-1 exhibited good sensitivity towards Rh6G over other colorants. This study provided a new strategy for construction of MIPs-based fluorescence sensors by introducing AIEgens as the fluorescence signal part, which will significantly expand the categories and application ranges of MIPs-based fluorescence sensors.

A novel fluorescent chemosensor (2) for the detection of Al(III) was designed based on the strategy of aggregation-induced emission (AIE), which was synthesized by introducing carboxyl group to tetraphenylethylene structure. 2 can bind with Al(III) to form chelate polymers with AIE characteristic, giving rise to an intense “turn-on” response in aqueous solution at pH 7.0. The binding stoichiometry of 2 toward Al(III) was in 1:1. High sensitivity and selectivity to Al(III) were achieved. A detection limit of 1.96 μmol L−1 and a linear rang of 0.0–50.0 μmol L−1 were obtained. Furthermore, 2 was successfully applied in detecting Al(III) in real water samples, which showed satisfactory recovery and accuracy.

Luminogens with aggregation-induced emission (AIE) characteristic drew extraordinary attention owing to their excellent luminescence properties in aggregated state or solid state, which showed wide application prospect in chemical sensing, bioimaging, lighting material and display material. In this work, a novel AIE molecule of (2,3-bis(4-(dimethylamino)phenyl)quinoxalin-6-yl)(phenyl)methanone (designated as LD-red) was facilely synthesized through a single-step reaction with commercially available materials. Based on its intrinsic twisted intramolecular charge transfer (TICT) characteristic, LD-red was successfully utilized as a reversible fluorescent thermometer. More importantly, LD-red exhibited good biocompatibility, which not only can be used as a probe for lipid droplets-specific imaging, but also can work as a promising photosensitizer to kill cancer cells through generation of reactive oxygen species (ROS) upon white light irradiation. LD-red enriches the kinds of AIEgens and, more importantly, this work provides a new strategy for constructing multifunctional AIEgen with TICT characteristic.

Photoresponsive materials with good luminescence property in solid state have shown promising applications in bio-imaging, photo-patterning, and optical switch related areas. However, most of the reported photoresponsive systems suffered from the drawbacks of either weak luminescence property in solid state or complex synthetic processes. In this work, a novel photoresponsive molecule of 2,3-diphenyl-6,7-dicyanoquinoxaline (PCQ) has been facilely prepared via one-step reaction with commercially available materials. PCQ exhibits typical aggregation-induced emission (AIE) property due to the mechanism of restricted intramolecular rotation (RIR). As a photoresponsive molecule, PCQ shows remarkable fluorescence changes both in solution and in solid state upon UV light irradiation. Mechanism study reveals that there is an UV light-induced isomerization reaction in PCQ. A good linear relationship between fluorescence intensity and UV light power density is achieved, which suggests that PCQ can be served as a sensor for monitoring UV light strength. Furthermore, characters are successfully recorded on PCQ in solid matrix, demonstrating the feasible application of PCQ in photo-patterning. The conspicuous contrast between the states before and after UV light irradiation suggests that PCQ can be potentially used as an anti-counterfeiting material. PCQ enriches the kinds of AIE luminogen (AIEgen) and, more importantly, this work provides a new strategy for constructing multifunctional photoresponsive systems with good luminescence property.

Photo-responsive materials with good luminescence performance in solid state have received widespread attention. However, the reported luminescent photo-responsive systems exhibit either only color change or both color and luminescence changes in solid state upon UV light irradiation. Developing photo-responsive materials with only tunable luminescence signals in solid state remains a great challenge for constructing concealed anti-counterfeit materials. In this work, a novel luminescent photo-responsive molecule (TPE-TS) was developed, which exhibited intense fluorescence emission due to the aggregation-induced emission (AIE) characteristic from its tetraphenylethene moiety. After irradiated by UV light, an isomerization from thio-keto form to thio-enol form took place in the thiosemicarbazide group, accompanied with obvious fluorescence quenching. Interestingly, there was no visible color variation before and after UV light irradiation owing to the small conjugated structure of TPE-TS. Taking this unique photo-responsive property, a concealed anti-counterfeit paper was successfully prepared. Letters could be recorded by UV light on this paper, hided under daylight and only visible again by UV light, demonstrating an excellent concealed performance as an anti-counterfeit material.