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A selective fluorescent paper sensor, consisting of an ionic liquid ([DBUH]+[Im]−) and a fluorophore (ANT-PPh3), can reversibly detect CO2 with fluorescence enhancement.

The machining accuracy of a copper electrode gear (CEG), especially the pitch deviation of CEG, is affected by the wear of the ball end mill (BEM) with the increase of the length of milling path. Based on the error mapping principle, this work focuses on the influence of BEM wear on pitch deviation. In order to dynamically compensate the influence of the BEM wear on pitch deviation, a novel milling pitch deviation compensation model was proposed based on the formation mechanism and measurement principle of pitch deviation. To ensure the uniform wear at the milling edge of the BEM during the milling process, BEM wear was firstly copied to the pitch deviation according to the tooth-by-tooth milling strategy. Then, the BEM wear curve was fitted based on orthogonal experiments and multiple linear regression. According to the wear curve, an offline compensation method was adopted to compensate for the pitch deviation caused by BEM wear. In addition, the reverse compensation principle was used to compensate for the normal deviation of BEM milling path. Finally, the compensation model was verified by milling experiments. Pitch deviation met the requirements of Levels 4 $\sim $ 5 in GB/T 38192-2019. The model can be used to guide the milling process of CEG.

Milling has the characteristics of flexibility and versatility, and can largely reduce the production cycle of customized tools. This study aims to mill helical surfaces of uniform roughness with universal tools in four-axis CNC machine tools through designing the optimal milling path. The transverse profile of the involute gear is modeled by the analytical method and the equidistant profile of the transverse profile is established by using the principle of normal offset to provide a theoretical tool position for tool paths. Aiming at the problem of unequal adjacent line spacing generated in the determination of the number of feed lines based on a constant angle, a determination method of the number of feed lines based on a constant arc length is proposed. In this method, according to the principle of calculus, the arc length of the involute curve is calculated to determine the proper number of feed lines which allows the scallop height to be approximately uniformly distributed on the tooth surface. In milling experiments, the processing efficiencies of LRTSLBL milling and LRTSTBT milling were confirmed and the peak of pitch under a small volume of tool wear was avoided by LRTSLBL milling. Importantly, the skip tooth machining test by LRTSTBT milling confirmed the cause for pitch peak and provided the basis for pitch error compensation.

Functionalized oligonucleotides (ONs) are widely applied as target recognition molecules for biosensing and gene regulation. Herein, we describe a general method for post-synthetic modification of ONs based on the oxidative amination of 4-thio-2'-deoxyuridine (4SdU) with sodium periodate and several amines. Alkyne-/azide-, biotin-, and fluorophore-modified ONs were prepared by modifying 4SdU-containing ONs with the corresponding amines and characterized for their bioorthogonal reactivity, streptavidin-binding affinity, and fluorescence properties, respectively. We synthesized three fluorophore-modified ONs with and without the aromatic fluorophores conjugated to modified nucleobases and investigated their emission properties. © 2021 Wiley Periodicals LLC. Basic Protocol 1: Post-synthetic modification of ONs Supporting Protocol: Preparation of dansyl ethylenediamine Basic Protocol 2: Quantification of ON reaction yields Basic Protocol 3: Characterization of modified ONs.

Carbon and nitrogen play a fundamental role in the production of

Acetone serves as a routine solvent and synthetic intermediate in chemical factories and laboratories. Monitoring the level of acetone vapor in working environment is of great necessity to employee health due to its strong volatility and toxicity, but there is still in lack of simple and easy-to-use portable sensors. In this study, we report a portable and intuitive indicator for real-time displaying acetone vapor concentration in air, based on the ratiometric fluorescence response of the designed organic molecule, PhB-SSB, to acetone. As an aggregation-induced emission (AIE) fluorophore, PhB-SSB underwent specific reaction with acetone through the salicylaldehyde Schiff base and phenylboronate groups to realize ratiometric fluorescence change from green to red after acetone vapor treatment. The reaction mechanism was proposed as acetone-induced breakage of the imine bond in PhB-SSB. We further fabricated PhB-SSB into a film fluorescent sensor for acetone vapor with good sensitivity and selectivity. Taking advantage of its intuitive fluorescent color contrast, acetone-specific response and small size, our sensor is practical in real-time alarming the acetone vapor hazard in the workplaces.

Lipid order in the cytoplasm membrane of eukaryotic cells undergoes dynamic changes in almost all cellular processes. Dynamically monitoring these changes is of essential biological significance and remains challenging. This work provides the first aggregation-induced emission probe, TPNPDA-C15, with highly three-dimensional specificity to cell membranes for fluorescent imaging of lipid order of live cells. TPNPDA-C15 displays red fluorescence enhancement with the viscosity increase while emits yellow fluorescence when aggregates form. Imaging analyses of giant unilamellar vesicles and live cells under osmotic shock by the probe demonstrate its sensitive response to the degree of phospholipids packing on artificial and cell membranes. Taking advantage of its superior low photocytotoxicity and high photostability, TPNPDA-C15 is further applied for long-term dynamic imaging of entire live cell physiological processes including apoptosis, ferroptosis, and mitosis in the dual-color mode. With the analysis of fluorescence signal changes in the two fluorescence channels, TPNPDA-C15 serves as a robust fluorescent probe for the imaging study of cellular dynamics.

Tuning fluorescence colour of solid-state materials has become a topic of increasing interest for both fundamental mechanism study and practical applications such as sensors, optical recording and security printing. In this work, a fluorescent colour tuneable molecule BA-C16 is rationally designed and facilely synthesized by attaching flexible long alkyl chains to 2-hydroxybenzophenone azine (BA), which shows both aggregation-induced emission (AIE) and excited-state intramolecular proton transfer (ESIPT) characteristics. Compared to BA, the simple introduction of long alkyl chains in BA-C16 leads to an emission wavelength redshift from 542 to 558 nm. This strategy of extending emission wavelength is rarely reported, and is ascribed to the enlarged through-space π-conjugation between interplanar molecules in the aggregate of BA-C16. Three crystals of BA-C16 are obtained with green, yellowish green and yellow emission. According to characterization by X-ray crystallography, X-ray powder diffraction and differential scanning calorimetry, alkyl chains play an important role in inducing different stacking modes of the three crystals, which further leads to polymorph-dependent fluorescence colour. BA-C16 exhibits tuneable solid-state fluorescence upon vapor fumigation, or annealing based on a transition between a "near-monomer" crystalline state and a "dimer" crystalline state. BA-C16 is further applied for rewritable fluorescence printing tuned by vapor- and thermal-treatment.

The uranyl-dependent DNAzyme 39E cleaves its nucleic acid substrate in the presence of uranyl ion (UO22+). It has been widely utilized in many sensor designs for selective and sensitive detection of UO22+ in the environment and inside live cells. In this work, by inserting a flexible linker (C3 Spacer) into one critical site (A20) of the 39E catalytic core, we successfully enhanced the original catalytic activity of 39E up to 8.1-fold at low UO22+ concentrations. Applying such a modified DNAzyme (39E-A20-C3) in a label-free fluorescent sensor for UO22+ detection achieved more than 1 order of magnitude sensitivity enhancement over using native 39E, with the UO22+ detection limit improved from 2.6 nM (0.63 ppb) to 0.19 nM (0.047 ppb), while the high selectivity to UO22+ over other metal ions was fully preserved. The method was also successfully applied for the detection of UO22+-spiked environmental water samples to demonstrate its practical usefulness.

A fluorescence "turn-on" method for digestion-free analysis of 4-thiouridine (s4U) in nucleic acids was developed in this work based on the oxidative amination of s4U by fluoresceinamine (FAM-NH2) and periodate (IO4-). It was 125-fold more sensitive for s4U detection than the traditional UV330 absorption method, and showed excellent selectivity to s4U over 2-thiouridine (s2U) analogues and biological thiols.

Functionalized oligonucleotides (ONs) are widely applied as target binding molecules for biosensing and regulators for gene expression. Numerous efforts have been focused on developing facile methods for preparing these useful ONs carrying diverse modifications. Herein, we present a general method for postsynthetic modification of ONs via oxidative amination of 4-thio-2'-deoxyuridine (4SdU). 4SdU-containing ON can be derived by both alkyl and aromatic amines. Using this approach, ONs are successfully attached with alkyne/azide, biotin and dansylamide moieties, and these as-prepared ONs possess the expected biorthogonal reactivity, streptavidin affinity and fluorescent property, respectively. Furthermore, we also directly install fluorophores to the ON nucleobase based on oxidative amination of 4SdU, and these fluorophores exhibit distinct luminescence behaviors before and after conjugation. We believe our method will be a versatile strategy for constructing various functionalized ONs used in a wide range of nucleic acid applications.

Optical imaging-guided photodynamic therapy (PDT), with precise localization and non-invasive treatment of tumors, is an emerging technique with great potential for cancer therapy. However, impaired by tissue auto-fluorescence that causes low signal-to-background ratio (SBR), most fluorescence imaging systems show poor sensitivity to tumors in vivo . In this study, we synthesized organic nanoparticles (ONPs) with persistent luminescence and good biocompatibility for afterglow imaging-guided PDT. The ONPs displayed near-infrared light emission with half-life time at minute level, which offered high SBR and good tissue penetration for in vivo afterglow tumor imaging. Taking advantage of their abundant singlet oxygen generation by NIR laser irradiation guided to the tumor sites, the ONPs also enabled imaging-guided PDT for efficient suppression of tumor growth in mice with minimal damage to major organs.

Analysis of subcellular organelles (e.g., a cytoplasm membrane and mitochondria) during cellular processes can provide particularly useful information for our understanding of cell chemistry and biology. For this purpose, fluorescent probes capable of dynamically imaging multiple organelles in a simultaneous and selective manner are highly demanded, yet such probes are scarcely reported due to the challenges in molecular design. In this study, we developed a dual-colored aggregation-induced emission (AIE) probe TPNPDA-C12 with twisted intramolecular charge transfer (TICT) to visualize the membrane and mitochondria of the same cells through distinct fluorescence channels simultaneously. We also successfully used the probe to monitor and distinguish the dynamic changes of the organelles during cell apoptosis and necrosis induced by reactive oxygen species (ROS) and cytotoxins.

A novel fluorescent probe DNBS-CSA is developed for light-up detection of β-lactamase. The probe design is based on an indirect detection approach with three step reactions. β-Lactamase can react with the lactam of its substrate (cefazolin sodium) to produce a secondary amine, initiating a spontaneous elimination reaction and affording a thiol compound. The thiol could further react with the sulfonate group of DNBS-CSA, releasing the salicylaldehyde azine derivative (CSA) with both aggregation induced emission (AIE) and excited-state intramolecular proton transfer (ESIPT) characteristics. Previously reported β-lactamase probes require covalent linkage of the substrate β-lactam ring part to the probe, which makes probe synthesis difficult due to the complicated structure of the β-lactam ring. In contrast, modification of the β-lactam ring is no longer necessary for DNBS-CSA according to our indirect detection approach. The linear range of fluorescence quantification for β-lactamase is 0-10 mU mL-1 in an aqueous solution. Moreover, owing to the AIE properties of CSA, detection of β-lactamase with DNBS-CSA on test papers was also achieved.

In this paper, mechanoresponsive fluorescent molecules with high “off–on” contrast ratios that undergo molecular packing transformation from amorphous phase to crystalline by scratching are first reported. Three 2-aminobenzophenone derivatives 1, 2, and 3, which possess crystallization-induced fluorescence characteristics, exhibited bright cyan, blue, and green fluorescence colors with “off–on” contrast ratios as high as 175-fold by scratching. The scratching induced transformation from amorphous phase to crystalline of 1, 2, and 3 were directly observed by XRD and SEM studies. In addition, the fluorescence of the scratched sample can readily convert back into the initial nonfluorescent state by fuming in ethanol or heating. Letters with three fluorescence emission colors of 1, 2, and 3 in ethanol solution smeared on a glass surface can be easily written by scratching and erased by fumigation, demonstrating the potential value as reversible mechanoresponsive fluorescent materials.

A ratiometric fluorescence detection method for trace amount of uranyl ion (UO 2 2+ ) was developed in this study, based on aggregation induced emission enhancement (AIEE) characteristics of 3-hydroxyflavone salicylaldehyde azine (HFSA) and luminescent signal of UO 2 2+ -HFSA complex in soluble state. The fluorescent ratio ( I 457 / I 534 ) was linearly related to the concentration of UO 2 2+ in the range of 0.5–20 ppb (part per billion). Analytical data showed that a detection limit of 0.5 ppb was achieved with the relative standard deviation (R.S.D.) 1.3% ( n =5). The proposed method could also be utilized for imaging UO 2 2+ in living cells by ratiometric fluorescence changes.

Triphenylmethanol (TPOH) is a non-fluorescent compound. Interestingly, after UV irradiation at 254 nm, TPOH showed a strong blue fluorescence on a solid surface. Moreover, the fluorescence can be quenched by UV irradiation at 365 nm, making the photoactivatable fluorescence reversible. TPOH is thus applied for rewritable photopatterning tuned by UV light.

Peroxidase-mimicking DNAzymes containing G-quadruplex structures are widely applied in chemistry as catalysts and signal amplification for biosensing. Enhancing the catalytic activity of these DNAzymes can therefore improve the performance of many catalysts and biosensors using them. In this work, we synthesized cationic peptide conjugates of peroxidase-mimicking DNAzymes, which were found to exhibit both enhanced peroxidase and oxidase activities up to 4-fold and 3-fold compared with the original DNAzymes, respectively. Further investigation suggested that the enhanced activity was ascribed to the stabilization of parallel DNA G-quadruplex structures and hemin binding by the cationic peptide covalently attached to the DNAzyme. Such a mechanism of activity enhancement was successfully utilized for biosensing applications with improved sensitivity and broadened target range. Hydrogen peroxide (H2O2) detection in K(+)-free solutions by the DNAzyme-peptide conjugate showed 2-fold sensitivity enhancement over the unmodified DNAzyme under the same condition, and the activity switch by target-induced cleavage of the DNAzyme-peptide conjugate was also used for the detection of caspase 3 protease with enzymatic amplification in homogeneous solutions.

DNA aptazymes are allosteric DNAzymes activated by the targets of DNA aptamers. They take the advantages of both aptamers and DNAzymes, which can recognize specific targets with high selectivity and catalyze multiple-turnover reactions for signal amplification, respectively, and have shown their great promise in many analytical applications. So far, however, the available examples of DNA aptazyme sensors are still limited in utilizing only several DNAzymes and DNA aptamers, most likely due to the lack of a general and simple approach for rational design. Herein, we have developed such a general approach for designing fluorescent DNA aptazyme sensors. In this approach, aptamers and DNAzymes are connected at the ends to avoid any change in their original sequences, therefore enabling the general use of different aptamers and DNAzymes in the design. Upon activation of the aptazymes by the targets of interest, the rate of fluorescence enhancement via the cleavage of a dually labeled substrate by the active aptazymes is then monitored for target quantification. Two DNAzymes and two aptamers are used as examples for the design of three fluorescent aptazyme sensors, and they all show high selectivity and sensitivity for the detection of their targets. More DNA aptazyme sensors for a broader range of targets could be developed by this general approach as long as suitable DNAzymes and aptamers are used.

A novel fluorescent probe SA-βGal is reported here with light-up response to β-galactosidase. SA-βGal possesses the β-galactopyranoside group to react with β-galactosidase and releases the fluorescent salicylaldehyde azine with both aggregation induced emission (AIE) and excited-state intramolecular proton transfer (ESIPT) characteristics. The linear fluorescent response enables the in vitro quantification of β-galactosidase activity in a range of 0–0.1 U mL−1 with a detection limit of 0.014 U mL−1. The probe exhibits significant advantages, such as no self-quenching at high concentrations, a large Stokes shift (190 nm) and high specificity to β-galactosidase with an excellent light-up ratio of 820 fold. Moreover, thanks to its good retention in living cells, the application of SA-βGal for the imaging of cellular β-galactosidase was also achieved with high contrast.

4-Chloro-2-(((2-hydroxybenzylidene)hydrazono)methyl)phenol (1) was reported to exhibit typical aggregation-induced emission (AIE) characteristics in our previous work. Here we introduce an acryloyl group onto the hydroxyl moiety of 1 and develop 2 (4-chloro-2-(((2-hydroxybenzylidene)hydrazono)methyl)phenyl acrylate) for fluorescence turn-on detection of cysteine (Cys). 1H-NMR and mass spectrometry data of the products revealed that the reaction between 2 and Cys resulted in the formation of 1 with excited-state intramolecular proton transfer (ESIPT) and AIE properties. With fluorescence enhancement detection by 2, the linear range and detection limit for Cys were obtained to be 0–30 μM (R2 = 0.998) and 0.46 μM respectively with satisfactory selectivity over homocysteine (GSH), glutathione (Hcy) and other amino acids. The method was also used for Cys detection in a serum sample.

5-Chlorosalicylaldehyde azine (1) has been reported to exhibit a typical aggregation-induced emission (AIE) feature in our previous work. In this work, we further discovered that AIE fluorescence of 1 could be selectively quenched by Cu2+, hence 1 and Cu2+ complex was applied as a turn-on fluorescence probe for pyrophosphate (PPi) detection in aqueous solution. 1H-NMR data of the isolated products revealed that the addition of PPi underwent displacement of 1 in 1–Cu2+ complex, which led to the release of free 1 to aqueous solution, resulting in recovered AIE fluorescence. With fluorescence enhancement detection by the 1–Cu2+ complex, the linear range and detection limit for PPi were obtained as 0–15 μmol L−1 (R2 = 0.997) and 0.064 μmol L−1, respectively, with satisfactory selectivity over other anions. The method was also used for PPi detection in serum samples.

The development of red fluorophores with efficient solid-state emission is still challenging. Herein, a red fluorophore 1 with aggregation-induced emission (AIE) and excited-state intramolecular proton transfer (ESIPT) characteristics is rationally designed and facilely synthesized by attaching an electron-donor diethylamine and an electron-acceptor maleonitrile group to salicyladazine. In contrast to many red fluorophores which undergo serious aggregation-caused quenching (ACQ), compound 1 emits bright red fluorescence (λem = 650 nm, ΦF = 24.3%) in the solid state with a large Stokes shift of 174 nm. Interestingly, control compounds 2 and 3, which have similar structures as 1, exhibit obvious aggregation-caused quenching (ACQ) characteristics. The difference in the crystal structures of 1, 2, and 3 reveals that the interplanar spacing among molecules plays a decisive role in realizing the AIE characteristics of 1. Moreover, when the hydroxyl group of 1 was substituted by an esterase reactive acetoxyl, a ...

A fluorescent chemosensor for Cu2+ has been developed based on the aggregation-induced emission (AIE) characteristics of bis(pyridin-2-ylmethylene) terephthalohydrazide (1). The dye molecule 1 exhibits a large Stokes shift of ~182 nm and shows highly sensitive and selective response to Cu2+ over other metal ions by forming a 1:2 metal-to-ligand complex in aqueous solution. Cu2+-induced fluorescence quenching at 516 nm was proportional to the concentration of Cu2+ in the range of 0.2–8.0 μM, with a detection limit as low as 160 nM. In addition, by taking advantage of its AIE characteristics, compound 1 can also enable the fabrication of test papers for in-field detections, which is challenging for many other fluorescent Cu2+ sensors due to their strong self-quenching effect in solid state.

A turn-on fluorescent probe DNBS-CSA is reported here with selective detection of thiols over other amino acids. Probe DNBS-CSA possesses the widely-used thiol-selective 2,4-dinitrobenzenesulfonyl (DNBS) group to react with thiols and release the fluorescent salicylaldehyde azine with aggregation-induced emission (AIE) characteristics. The use of AIE dye prevented the sensor from aggregation-induced fluorescence quenching which is challenging for other thiols sensors. Upon the addition of cysteine (Cys) to DNBS-CSA in aqueous solution (10 mM PBS buffer at pH 7.4 containing 30% DMSO), an intense fluorescence enhancement was observed at 558 nm with a large stokes shift of ∼170 nm. Under the optimal condition, the fluorescence intensity linearly increased with the concentration of Cys in the range of 8–18 μM with a correlation coefficient of R2 = 0.991. The fluorescence enhancement of DNBS-CSA upon addition of Cys on test paper was also observed, enabling DNBS-CSA function as solid materials (such as test papers) for thiols detection. The detection of thiols in serum samples was successfully performed. With good cell permeability, the probe was applied to the imaging of thiols in HEK 293T cells.

A ratiometric fluorescent chemosensor 1 was developed for the detection of Al3+ in aqueous solution based on aggregation-induced emmision (AIE). The chemosensor showed the fluorescence of its aggregated state and Al3+-chelated soluble state in the absence and in the presence of Al3+, respectively, and resulted in a fluorescence ratio (I461/I537) response to Al3+ in neutral aqueous solution at a detection limit as low as 0.29 μmol L−1. The method was also highly selective to Al3+ over other physiological relevant metal ions investigated in this study. Taking advantage of its AIE characteristics, the chemosensor was successfully applied on test papers for simple and rapid detection of Al3+. Moreover, the application of 1 for the imaging of Al3+ in living cells by ratiometric fluorescence changes was also achieved.

Photochromic molecules are widely applied in chemistry, physics, biology, and materials science. Although a few photochromic systems have been developed before, their applications are still limited by complicated synthesis, low fatigue resistance, or incomplete light conversion. Rhodamine is a class of dyes with excellent optical properties including long-wavelength absorption, large absorption coefficient, and high photostability in its ring-open form. It is an ideal chromophore for the development of new photochromic systems. However, known photochromic rhodamine derivatives, such as amides, exhibit only millisecond lifetimes in their colored ring-open forms, making their application very limited and difficult. In this work, rhodamine B salicylaldehyde hydrazone metal complex was found to undergo intramolecular ring-open reactions upon UV irradiation, which led to a distinct color and fluorescence change both in solution and in solid matrix. The complex showed good fatigue resistance for the reversible photochromism and long lifetime for the ring-open state. Interestingly, the thermal bleaching rate was tunable by using different metal ions, temperatures, solvents, and chemical substitutions. It was proposed that UV light promoted isomerization of the rhodamine B derivative from enol-form to keto-form, which induced ring-opening of the rhodamine spirolactam in the complex to generate color. The photochromic system was successfully applied for photoprinting and UV strength measurement in the solid state. As compared to other reported photochromic molecules, the system in this study has its advantages of facile synthesis and tunable thermal bleaching rate, and also provides new insights into the development of photochromic materials based on metal complex and spirolactam-containing dyes.

This study investigates the heavy-atom effect (HAE) on aggregation-induced emission enhancement (AIEE) properties of salicylaldehyde azines. For this purpose, a series of halogenated salicylaldehyde azine derivatives, namely, chloro-salicylaldehyde azine (1), bromo-salicylaldehyde azine (2) and iodo-salicylaldehyde azine (3) are synthesized. 1 and 2 display typical AIEE characteristics of salicylaldehyde azine compounds; whereas for the iodo-substituent in 3, is found to be effective “external” heavy atom quenchers to salicylaldehyde azine fluorescence in aggregated state. Based on its weak fluorescence in aggregated state and relative strong fluorescence in dispersed state, 3 can also be applied as a turn-on fluorescence probe for egg albumin detection attributed to hydrophobic interaction.

A facile, rapidly responsive fluorescence turn-on probe for heparin with high selectivity and sensitivity was reported in this paper. The probe could aggregate on the negatively charged heparin template through electrostatic interactions and then display intense fluorescence due to its aggregation-induced emission (AIE) characteristics. Under optimal condition, the probe showed high selectivity to heparin over chondroitin sulfate(ChS), hyaluronic acid (HA), dextran (DeX) and other substances, with a linear range of 0.2–14 μg/mL, and a detection limit of 57.6 ng/mL. In diluted serum, it also showed good performance.

A series of salicylaldehyde-2-pyridinehydrazone derivatives were found to exhibit interesting “turn-on” fluorescence response toward Zn 2+ in water at neutral pH, which could be prepared readily from commercially available materials through a one-step reaction in ethanol at room temperature. Among these compounds, 1 showed a 22-fold fluorescence enhancement in 99% water/DMSO (v/v) at pH 7.0 with a linear range of 0.10–1.00 μmol/L and detection limit of 30 nmol/L Zn 2+ . Especially, 1 was not affected by Cd 2+ which usually induced a comparable fluorescence response to that of Zn 2+ in other reported works. Moreover, live cell imaging showed that 1 could be useful for monitoring Zn 2+ within biological samples.

In this work, (2-hydroxy-4-methoxyphenyl)(phenyl)methanone azine (1) was found to exhibit aggregation-induced emission (AIE) and tunable solid fluorescence upon alternate annealing/melting treatments. According to the characterizations by X-ray crystallography, X-ray powder diffraction, and differential scanning calorimetry, the switching between the two different polymorphs was responsible for the tunable solid fluorescence as a consequence of polymorph-dependent excited-state intramolecular proton transfer (ESIPT) fluorescence, while the thermochromism was contributed by the conformational flexibility of rotary phenyl rings. The change in the tightness of packing upon annealing or melting thermal treatments resulted in the emission at different wavelengths. Therefore, polymorph-dependent ESIPT fluorescence could be utilized as a new strategy to develop efficient AIE-active materials in response to external stimuli.

Fluorescein hydrozide modified silica nanoparticles (FH-SNPs, 280–550 nm) were prepared by covalently immobilizing a fluorescein hydrozide (FH) derivative containing organosilyl ligands onto the surface of silica nanoparticles. FT-IR, elemental analysis, SEM microscopy and steady-state fluorescence anisotropy were used to characterize the functionalized FH-SNPs. Upon the addition of Cu(II), the spirolactam ring of FH moiety on the silica surface was opened and a fluorescent product was formed, exhibiting a selective Cu(II)-amplified fluorescence signal. Under the optimized conditions, the linear range of fluorescence intensity for Cu(II) is 5–80 μM ( R 2 = 0.992), and the limit detection for Cu(II) is 1.0 μM according to IUPAC definition ( C LOD = 3.3 S b / m ).