Search

A near-infrared (NIR) mechanophore was developed and incorporated into a poly(methyl acrylate) chain to showcase the first force-induced NIR chromism in polymeric materials. This mechanophore, based on benzo[1,3]oxazine (OX) fused with a heptamethine cyanine moiety, exhibited NIR mechanochromism in solution, thin-film, and bulk states. The mechanochemical activity was validated using UV-vis-NIR absorption/fluorescence spectroscopies, gel permeation chromatography (GPC), NMR, and DFT simulations. Our work demonstrates that NIR mechanochromic polymers have considerable potential in mechanical force sensing, damage detection, bioimaging, and biomechanics.

Luminescent conjugated network polymer is one of the most promising chemo-sensors owing to their good chemical/optical stability and multiple functionalization. Herein, three conjugated network polymers were prepared by using aggregation-induced emission active 1,1,2,2-tetrakis(4-formyl-(1,1′-biphenyl))-ethane (TFBE) unit as monomer and hydrazine as linker. Through regulating the synthetical condition, the polymeric network can form either uniform two-dimensional azine-linked nanosheets (A-NS), conjugated microporous polymers (A-CMP) or covalent organic frameworks (A-COF). All of these polymers exhibited good stability and high fluorescence quantum efficiency with the quantum yield of 6.31% for A-NS, 5.26% for A-CMP, and 5.80% for A-COF, as well as fast and selective fluorescence quenching response to 2,4,6-trinitrophenol (TNP). And the best TNP sensing performance with the Stern-Volmer constants (Ksv) values up to 8 × 105 L/mol and a detection limit of 0.09 μmol/L was obtained for A-NS. The study explores various strategies to construct conjugated polymers with different nanoarchitectures based on the same building block for sensitive detection of explosives.

Photoinduced electron transfer (PET) is one of the most important mechanisms for developing fluorescent probes and biosensors. Quantitative prediction of the quantum yields of these probes and sensors is crucial to accelerate the rational development of novel PET-based functional materials. Herein, we developed a general descriptor (ΔE) for predicting the quantum yield of PET probes, with a threshold value of ∼0.6 eV. When ΔE ∼0.6 eV, the quantum yield is high because of the inhibition of PET. This simple yet effective descriptor is applicable to a wide range of fluorophores, such as BODIPY, fluorescein, rhodamine, and Si-rhodamine. This ΔE descriptor enables us not only to establish new applications for existing PET probes but also to quantitatively design novel PET-based fluorophores for wash-free bioimaging and AIEgen development.

The development of conjugated nanomaterials with high sensitivity and super-amplified quenching effect for the detection of nitrophenol explosives is still a great challenge. Herein, we developed conjugated hollow nanospheres constructed by using aggregation-induced emission (AIE) active 1,3,5-tris(4-formyl-phenyl)benzene (TFPB). The high emission hollow nanospheres with uniform size and admirable dispersiveness exhibited obvious fluorescence quenching response with the addition of nitrophenol explosives owing to the photoinduced electron transfer (PET) from the hollow nanospheres to nitrophenol explosives. The Stern-Volmer constants of hollow spheres for 2,4,6-trinitrophenol (TNP), 4-nitrophenol (NP) and 2,4-dinitrophenol (DNP) can reach 9.67×105, 3.14×105 and 4.8×104 M−1, respectively. Furthermore, the handy test paper coated with hollow nanospheres was prepared and showed a good response toward TNP solutions and vapor. The study provides a novel strategy to construct AIE-active conjugated hollow nanospheres for efficient nitrophenol explosives sensing.

Polymorphism makes it possible to clarify the relationship between emission property and crystal structure. However, based on the exact molecular conformation in tetraphenylethene polymorphisms, it is still challenging to evaluate the difference of intramolecular coplanarity without the support of calculation because of the complex combination of four different torsion angles between four peripheral benzenes and the central ethylene plane. Here, by using a di-formyl-functionalized tetraphenylethene derivative, two ideal polymorphisms with a consistent trend of the corresponding torsion angles have been obtained. For the first time, we explicitly demonstrated that intramolecular coplanarity is the underlying cause of the polymorphism-dependent emission of tetraphenylethene derivatives.

Rhodamine spirolactam based photoswitches have been extensively applied in super-resolution single-molecule localization microscopy (SMLM). However, the ring-opening reactions of spirolactams are cross-sensitive to acid, limiting their photoswitch use to neutral pH conditions. In addition, the ring-closing reactions of spirolactams are environment-sensitive and slow (up to hours), virtually making rhodamine spirolactams caged fluorescent dyes instead of reversible photoswitches in SMLM. Herein, by introducing hydrogen bonds to stabilize spirolactams, we report a series of acid-resistant rhodamine spirolactams with accelerated ring-closing reactions from fluorescent xanthyliums to non-fluorescent spirolactams, endowing them with good photoswitchable properties even in acidic environments. By further substitution of 6-phenylethynyl naphthalimide on the spirolactam, we shifted the photoactivation wavelength into the visible region (>400 nm). Subsequently, we have successfully applied these dyes in labeling and imaging the cell surface of Bacillus subtilis at pH 4.5 using SMLM.

Rhodamine B-naphthalimide (RhB-Naph) demonstrated a distinct aggregation-induced emission (AIE) mechanism, different from the restriction of intramolecular rotations or vibrations as in traditional AIE molecules. The monomers of RhB-Naph were non-emissive, due to the presence of a dark S1 state. Upon molecular aggregation, intermolecular interactions significantly altered the electronic properties of RhB-Naph, leading to the formation of a bright S1 state and endowing RhB-Naph with notable AIE properties. Besides, we demonstrated that RhB-Naph enabled the development of a solid-state three-color fluorescent switch upon multi-external stimuli.

Herein, we provide a direct observation of the modulation of the excited state transition under mechanical and thermal stimuli in the solid state by two organic polymorphs based on a tetraphenylethene derivative (APMOB). It enriches the insight in the research of stimuli responsive luminescent materials.

Photoinduced electron transfer (PET) is one of the most important mechanisms for developing fluorescent probes and biosensors. Quantitative prediction of the quantum yields of these probes and sensors is crucial to accelerate the rational development of novel PET-based functional materials. Herein, we developed a general descriptor (Δ

Fluorescence thermometry based on organic dyes affords high spatial and temporal resolution with a simple system design and low cost, for measuring temperatures in microenvironments. Many fluorescent thermometers consist of two types of fluorophores with distinct temperature responses, and the ratios of their fluorescence intensities afford accurate temperature information. Yet, the reliability of these ratiometric thermometers is vulnerable to photobleaching induced system variations. In this paper, we have proposed and demonstrated a new strategy, to achieve ratiometric temperature measurements from 15 °C to 75 °C, based on ground-state conformational isomers of a single type of dye. These ground-state conformers emit bright fluorescence, in contrast to excited-state conformational changes that generally quench emissions. Moreover, thermal equilibrium of these conformers and their distinct spectra lead to ratiometric temperature readings that are not affected by photobleaching. We expect that our design strategy has significant implications for developing fluorescence thermometry with outstanding reliability.

A novel amphiphilic copolymer consisting of tetraphenylethylene-oxazolidine (TPE-OX) as a pH-sensitive chromophore and poly(ethylene glycol) methyl ether methacrylate (PEGMA) as a water-soluble chain has been well designed and synthesized. A self-assembled polymeric micelle based on the copolymer exhibited clear dual-emission switching between cyan and red with a decrease of pH value in Tris-HCl buffer solution due to the extended conjugation and emerging intramolecular charge transfer effect when opening the spiro-ring of OX moiety. Fluorescence imaging of HepG2 cells stained by the polymeric micelle shows switched luminescence from cyan to red with high selectivity and contrast, indicating that the polymeric micelle was an effective probe for intracellular pH detection. Additionally, the red emission of the polymeric micelle in lysosomes can reversibly switch back to the original cyan emission in response to the two lysosomal activity inhibitors chloroquine and bafilomycin, which demonstrates that the polymeric micelle has potential applications in detecting the activity of lysosomal and further autophagy in cancer cells.

Solid-state organic photoswitches with reversible luminescence modulation property are highly attractive because of their wide prospects in advanced photonic applications, such as optical data storage, anticounterfeiting and bioimaging. Yet, developing such materials has long been a significant challenge. In this work, we construct an efficient solid-state photoswitch based on a spiropyran-functionalized distyrylanthracene derivative (DSA-2SP) that exhibits exceptional reversible absorption/luminescence modulation ability. Efficient photoswitching between DSA-2SP and its photoisomer DSA-2MC are facilitated by large free volumes induced by nonplanar molecular structures of DSA moieties, as well as the intramolecular hydrogen bonds between the DSA and MC moieties. Consequently, the excellent solid-state photochromic property of DSA-2SP is highly applicable as both anticounterfeiting inks and super-resolution imaging agents.

The mechanochromic property of tetrakis(4-(dimethylamino)phenyl)ethylene (TDMAPE) with natural propeller shape and nearly centrosymmetric structure was investigated. The destruction of the crystalline structure leads to the planarization of molecular conformation, which is considered as a possible reason for the red-shift of absorption and fluorescence spectra after grinding. And the polymorphism-dependent emissions of the two polymorphs of TDMAPE are mainly determined by the intramolecular conformation, which show the increased coplanarity or conjugation degree, ultimately leading to the bathochromic shift of the emissions.

Two tetraphenylethene (TPE)-functionalized spiropyran (SP) molecules with very similar structure were designed and synthesized. The two molecules exhibit aggregation-induced emission (AIE) properties, as well as multistimuli-responsive color-changing properties, such as photochromism and acidchromism. The investigation of their different photochromic and acidchromic characteristics and dual-response fluorescent switch during isomerization indicated that the different link position between TPE and SP will significantly affect the extended π-conjugated system, resulting in completely different photochromic and acidchromic properties.

An overview of the mechanisms for mechanofluorochromic behaviors based on organic/polymer systems has been provided, and the most significant developments in understanding the origin of mechanofluorochromism have been highlighted. The views are mainly focused on the intermolecular effects and intramolecular effects on mechanofluorochromism, including excimer forming, phase structural transition, J- or H-aggregation and intramolecular coplanarity and so on. It should be helpful to researchers to understand more deeply the relationships between the molecular structures and the mechano-responsive behaviors.

A new multi-responsive tetraphenylethene functionalized oxazoline molecular switch (TPE-OX) was synthesized, which not only preserves isomerization and AIE properties, but also demonstrates synergistic effects, showing tunable multi-emission both in solution and in solid states.

Two methoxy-substituted tetraphenylethylene (TPE) derivatives, tetra(4-methoxyphenyl)ethylene (TMOE) and tetra(3,4-dimethoxyphenyl)ethylene (TDMOE), were synthesized by McMurry reaction in high yields. The nearly centrosymmetric and natural propeller shape of TMOE and TDMOE excluded intermolecular effects, such as H or J-aggregation and π–π stacking, on their AIE (AIEE) and mechanofluorochromic performance. The crystal structures of TMOE and TDMOE, and theoretical calculations proved that their emission colours are determined by single molecular conjugation. These molecules were used to investigate pure conformational effects on molecular emissions. The spectral properties of these molecules in five environments of crystal(s), THF solution, THF–water binary solution, solidified THF and amorphous states, were investigated. The crystalline to amorphous phase transition by grinding resulted in good mechanofluorochromic performances with high quantum yields and distinguishable emission change, which was further explored as anti-counterfeiting inks on banknotes.