Tunable Fluorescence Emission Research Articles

Rational design of 1, 2, 4, 5-tetraphenyl-1H-imidazole-based AIEgens with tunable intramolecular charge transfer and restricted intramolecular rotation processes for multifunctional sensing

Aggregation-induced emission fluorogens (AIEgens) with intramolecular charge transfer (ICT) characteristic are widely used in the detection of various analytes owing to their highly tunable fluorescence emission properties. However, facilely synthesis of AIEgens with ICT characteristic for multiple sensing is still rare and limited in use. In this work, two new AIEgens of 1,2-bis(4-alkoxycarbonylphenyl)-4,5-bis(4-methoxyphenyl)-1H-imidazole (AMI) and its hydrolyzed derivative 1,2-bis(4-carboxylphenyl)-4,5-bis(4-methoxyphenyl)-1H-imidazole (CMI) were facilely synthesized with donor-π-acceptor (D-π-A) structures. The tunable ICT and restricted intramolecular rotation (RIR) processes endow them multifunctional sensing performances. AMI could serve as a reversible fluorescent thermometer, in which a positive linear correlation between fluorescence intensities and temperatures from 20 °C to 60 °C was obtained. Meanwhile, owning to the specific interaction between carboxyl groups and Al(III) ions, CMI was successfully served as a “turn-on” fluorescent chemosensor for detecting Al(III) in aqueous solutions under a neutral condition with high sensitivity and selectivity. Mechanism study showed that the formation of aggregation states of coordination polymers between CMI and Al(III) was responsible for the fluorescence enhancement. What is more, the sensing process could be applied for detecting Al(III) in real water samples and on solid test papers, which implied its potential application values. Furthermore, the aggregation-induced emission (AIE) characteristic also made fluorescence emissions of CMI suitable for specific pH sensing. This work provides an efficient strategy for the construction of multifunctional fluorescence chemosensors based on AIEgens.

Reversible Multi-Color optical switch utilizing tetraphenylethylene and spiropyran Complexes: Applications in advanced information encryption

In this paper, we introduced a strategic methodology to obtain time-resolved encryption utilizing a new technique. This method utilizes a reversible supramolecular optical switch, which is based on complexes consisting of tetraphenylethylene and spiropyran. Notably, these components are separately attached at the focal point of the same cholesterol-based unit, wherein the cholesterol-based unit can provide the essential driving forces to form complexes. A series of complexes were prepared with varying molar ratios (TPE/SP), allowing for the tuning of fluorescence emission. The supramolecular system leverages hydrogen bonding, van der Waals forces, and other non-covalent interactions to orchestrate the collaboration between the fluorophores (tetraphenylethylene) and the photochromic molecule (spiropyran). This coordination results in exceptional photochromic attributes, including rapid response, high contrast, and the capability to regulate fluorescence. The system is capable of achieving tunable dynamic fluorescence emission that transitions from brilliant blue to light purple and finally to red through fluorescence resonance energy transfer (FRET) after successive irradiation periods. Additionally, by fine-tuning the ratio of tetraphenylethylene to spiropyran, different dynamic fluorescence emission can be precisely manipulated. It is rarely reported that complexes accomplish time-dependent fluorescence emission with high-contrast. We are confident that the complexes, grounded on cholesterol unit, hold promise for broader applicability in developing innovative time-dependent fluorescent materials. Such materials can be effectively utilized for time-dependent information encryption, thereby bolstering security measures against unauthorized access.

Sensing the Small Change of Intermolecular Distance in Supramolecular Assembly by Using the Tunable Emission Wavelength of AIE-Active Luminogens.

The distinct molecular states - single molecule, assembly, and aggregate - of two ionic macromolecules, TPPE-APOSS and TPE-APOSS, are easily distinguishable through their tunable fluorescence emission wavelengths, which reflect variations in intermolecular distances. Both ionic macromolecules contain aggregation-induced emission (AIE) active moieties whose emission wavelengths are directly correlated to their mutual distances in solution: far away from each other as individual molecules, maintaining a tunable and relatively long distance in electrostatic interactions-controlled blackberry-type assemblies (microphase separation), or approaching van der Waals close distance in aggregates (macrophase separation). Furthermore, within the blackberry assemblies, the emission wavelength decreases monotonically with increasing assembly size, indicative of shorter intermolecular distances at nanoscale. The emission changes of TPPE-APOSS blackberry assemblies can even be visually distinguishable by eyes when their sizes and intermolecular distances are tuned. Molecular dynamics simulations further revealed that macromolecules are confined in various conformations by controllable intermolecular distances within the blackberry structure, thereby resulting in fluorescence emission with tunable wavelength.

Rapid Construction of PVA@CDs/SiO2 Fluorescent/Structural Color Dual-Mode Anti-Counterfeiting Labels via Spray-Coating Method.

A method of sequential spraying of polyvinyl alcohol with carbon quantum dots (PVA@CDs) aqueous suspension and SiO2 aqueous suspension is proposed to rapidly prepare multicolor dual-mode anti-counterfeiting labels. With the optimization of the concentration (15%) of colloidal microspheres in the SiO2 aqueous suspension as well as the spraying process parameters (spray distance of 10 cm, spray duration of 3 s, and assembly temperature of 20 °C), different-sized SiO2 microspheres (168 nm, 228 nm, and 263 nm) were utilized to rapidly assemble red, green, and blue photonic crystals. Furthermore, the tunable fluorescence emission of carbon quantum dots endows the labels with yellow, green, and blue fluorescence. The constructed dual-mode labeling was used to develop an anti-counterfeiting code with dual-channel information storage capabilities and also to create dual-mode multicolor anti-counterfeiting labels on various packaging substrates. This work provides a novel solution for anti-counterfeiting packaging and information storage.

Multicolor Tuning of Perylene Diimides Dyes for Targeted Organelle Imaging In Vivo.

The adjustment of the emission wavelengths and cell permeability of the perylene diimides (PDI) for multicolor cell imaging is a great challenge. Herein, based on a bay-region substituent engineering strategy, multicolor perylene diimides (MCPDI) were rationally designed and synthesized by introducing azetidine substituents on the bay region of PDIs. With the fine-tuned electron-donating ability of the azetidine substituents, these MCPDI showed high brightness, orange, red, and near infrared (NIR) fluorescence along with Stokes shifts increasing from 35 to 110 nm. Interestingly, azetidine substituents distorted to the plane of the MCPDI dyes, and the twist angle of monosubstituted MCPDI was larger than that of disubstituted MCPDI, which might efficiently decrease their π-π stacking. Moreover, all of these MCPDI dyes were cell-permeable and selectively stained various organelles for multicolor imaging of multiple organelles in living cells. Two-color imaging of lipid droplets (LDs) and other organelles stained with MCPDI dyes was performed to reveal the interaction between the LDs and other organelles in living cells. Furthermore, a NIR-emitting MCPDI dye with a mitochondria-targeted characteristic was successfully applied for tumor-specific imaging. The facile synthesis, excellent stability, high brightness, tunable fluorescence emission, and Stokes shifts make these MCPDI promising fluorescent probes for biological applications.

Hydroxyl radical-mediated synthesis of carbonyl functionalized graphene quantum dots-like as enzyme mimics with tunable fluorescence emission

The synthesis of graphene quantum dots-like enriched with specific oxygenated groups (o-GQDs) exhibiting great catalytic performance offers a promising tool for diagnosis and biomedicine, but introducing specific oxygen groups remains a challenge. Here, we propose a mild synthetic protocol for producing regulated fluorescence emission (from blue to yellow) carbonyl functionalized GQDs with double catalytic function through Fe3O4-catalyzed hydroxyl radical (·OH) oxidation the precursors like graphene oxide, polyaniline (PANI) and polydopamine (PDA). The method can be carried out at room temperature than the traditional high-temperature oxidation in concentrated acid. Interestingly, o-GQDs exhibit excellent peroxidase (POD)- and ascorbate oxidase-like activity. XPS characterization showed a significant increase in carbonyl content in o-GQDs compared to the precursor, even a 14-fold increase in blue-emitting iron-doped GQDs (b-Fe-GQDs). The introduction of Fe3O4 during the synthesis process results in a minor degree of Fe doping, which enhances the catalytic activity of b-Fe-GQDs through coordination with N. Based on this feature, highly sensitive single-signal and ultra-selective dual-signal methods for alkaline phosphatase detection were developed. This low cost and safe synthesis strategy paves the way for practical usage of o-GQDs.

Multi-functional fluorescent silicon elastomer cross-linked with AIE polymer by dynamic imine bond and its application in anti-counterfeiting

Fluorescent elastomer materials have received extensive attention due to their excellent optical performance, flexibility, and chemical stability in recent years, and demonstrate great application potentials in intelligent sensors, optoelectronic devices, medical equipment and other fields. Although the traditional method for constructing fluorescent elastomers by doping fluorescent small molecules is facile and universal, it also has limitations such as low luminous efficiency, uneven dispersion, poor stability and single function. In this work, an aggregation-induced emission (AIE) fluorescent polymer with aldehyde groups in side chain was synthesized and crosslinked with aminopropyl double capped polydimethylsiloxane (NH2-PDMS-NH2) through mild Schiff base reaction to construct a fluorescent elastomer. Compared with fluorescent small molecules, AIE polymers have superior fluorescence performance and can be flexibly designed according to demands. The dynamic imine bonds endow the as-obtained elastomers with self-healing and recycling properties, enabling rapid repair and remodeling at room temperature. Besides, the tensile and swelling properties of PDMS enable them to adjust the concentration of fluorescent units in the matrix under corresponding stimulus, thereby achieving tunable fluorescence emission. Taking advantage of the fluorescent elastomers, we prepared fluorescent anti-counterfeiting patterns that were hidden in daylight and visible under UV light, demonstrating the potential applications of the fluorescent elastomers in the fields of anti-counterfeiting and information encryption. This study also provides an alternative strategy for developing multifunctional fluorescent elastomers.

Green hydrothermal synthesis of multifunctional carbon dots from cassava pulps for metal sensing, antioxidant, and mercury detoxification in plants

Carbon dots (CDs) have been attracted to nanocarbon materials for metal ion sensing, biological activity, and plant phytotoxicity due to their excellent photophysical properties, such as low cytotoxicity, high quantum yield, tunable fluorescence emission, and biocompatibility. Cassava pulp, which consists mainly of starch, has been identified as a low-cost biomass waste from the cassava starch industry. Therefore, this research developed CDs and nitrogen-doped CDs (NCDs) from cassava pulp using a one-step hydrothermal process in deionized water at 200 °C. The effects of the synthesis conditions, including reaction time (6–24 h) and the nitrogen doping derivatives, were also investigated. CDs and ethylenediamine doped-NCDs exhibited tunable fluorescence emission, strong quantum yield, high photostability, and tolerance to photobleaching. Furthermore, the potential applications of CDs-12 h were demonstrated such as fluorescent sensors for metal ion sensing, antioxidant activity, and mercury detoxification in plants. Fluorescence quenching of the CDs-12 h via both static and dynamic quenching mechanisms was observed in the presence of several metal ions such as Hg2+, Cu2+, and Fe3+ with the detection limit in micromolar levels and further applied to real water samples with good recovery and acceptable relative standard derivation. The paper test strip coated with CDs-12 h could also detect these metal ions under UV light. CDs and NCDs-EDA also showed potential DPPH radical scavenging activity and alleviated mercury toxicity in the Chinese cabbage seedlings with the incubation of CDs-12 h and NCDs-EDA-12 h (30 mg/L).

Facile synthesis of multicolor emitting sulfur quantum dots and their applications in light blocking field, anti-counterfeiting and sensing

Sulfur quantum dots (SQDs) have aroused widespread interest from researchers in a wide range of fields due to their excellent photoluminescent properties. Ethylenediamine, diaminopropane and butanediamine were used as precursor amine raw materials to interact with sublimated sulfur to synthesize SQDs with blue, cyan and green fluorescence emission, respectively. Multicolour emitting SQDs were first prepared via sulfur-amine interactions. Further characterization and calculations showed that the precursor amine substances could alter growth size and band gap energy of SQDs to allow for a wider absorption and fluorescence transfer to long wavelength emission region, resulting in tunable fluorescence emission. In terms of application, the excellent down-conversion properties of SQDs were utilized to obtain highly transparent and flexible photoblocking films by blending SQDs with polyvinyl alcohol matrixes, achieving a blocking of light in UV region of up to 99.69 %. In addition, we constructed an encoded storage microarray based on standard 8-bit ASCII character binary codes using BSQDs and GSQDs to store and encrypt important information. Finally, GSQDs-based fluorescent sensors were designed to achieve fluorescent trace detection of o-nitrophenols with limits of detection as low as 2.54 μM. The multicolor emitting SQDs prepared in this work have great potential for applications in analytical detection, optical anti-counterfeiting and light blocking.

Host-Guest Complexes of Pillar[5]arene as Components for Supramolecular Light-Harvesting Systems with Tunable Fluorescence.

A guest molecule containing a short alkyl spacer between the tetraphenylethylene group and the methylpyridinium group was designed and synthesized. After complexation with a water-soluble pillar[5]arene, the resulting host-guest complex can further self-assemble into fluorescence-emitting nanoparticles in water. By loading a commercially available dye Rhodamine 6G into the nanoparticles, an efficient artificial light-harvesting system with high donor/acceptor ratios (>400/1) was successfully constructed. The obtained systems show considerable antenna effects with values of more than 10 times. The system also exhibits tunable fluorescence emission behavior and can be used as a fluorescent ink for information encryption.

Facile Green Gamma Irradiation of Water Hyacinth Derived-Fluorescent Carbon Dots Functionalized Thiol Moiety for Metal Ion Detection.

Fluorescent sensor-based carbon dots (CDs) have significantly developed for sensing metal ions because of their great physical and optical properties, including tunable fluorescence emission, high fluorescence quantum yield, high sensitivity, non-toxicity, and biocompatibility. In this research, a green synthetic approach via simple gamma irradiation for the carbon dot synthesis from water hyacinth was developed since water hyacinth has been classified as an invasive aquatic plant containing cellulose, hemicellulose, and lignin. The thiol moiety (SH) was further functionalized on the surface functional groups of CDs as the "turn-off" fluorescent sensor for metal ion detection. Fluorescence emission displayed a red shift from 451 to 548nm when excited between 240 and 500nm. The quantum yield of CDs-SH was elucidated to be 13%, with strong blue fluorescence emission under ultraviolet irridiation (365nm), high photostability and no photobleaching. The limit of detection was determined at micromolar levels for Hg2+, Cu2+, and Fe3+. CDs-SH could be a real-time monitoring sensor for Hg2+ and Cu2+ as fluorescence quenching was observed within 2min. Furthermore, paper test-strip based CDs-SH could be applied to detect these metal ions.

Emissive fluoren-triangles for solid-state fluorochromism and selective gas sorption

•A fluorescent fluoren-triangle macrocycle is crafted •Intriguing solid-state fluorochromism capabilities are shown •Selective gas sorption performance is demonstrated In this work, we first present a new class of fluorescent synthetic macrocycle, named fluoren-triangle (FT), which we designed by creatively integrating the fluorene fluorophore into the resorcinarene backbone. Single-crystal analysis of FT revealed isosceles-triangle conformations accompanied by a layer-like molecular assembly in the solid state. Fluorescence experiments demonstrated its aggregation-induced emission character and tunable solid-state fluorescence emission, and per-methylated FT (MeFT) also exhibited an intriguing excitation-wavelength-dependent (Ex-De) capability with different emission color-switching processes. Significantly, the activated powders of per-hydroxylated FT (OHFT) and MeFT with both nonporous and amorphous features displayed remarkable potential in constructing adsorptive separation materials for CO2 and CH4 capture, affording good selectivities of 31/1 for CO2/N2 (by OHFT) and 8/1 for CH4/CO2 (by MeFT), respectively. The discovery of FT will provide new perspectives in constructing novel fluorescent macrocycles and functional photo-responsive materials, unleashing new inspirations in molecular sorbents for gas adsorption and separation. In this work, we first present a new class of fluorescent synthetic macrocycle, named fluoren-triangle (FT), which we designed by creatively integrating the fluorene fluorophore into the resorcinarene backbone. Single-crystal analysis of FT revealed isosceles-triangle conformations accompanied by a layer-like molecular assembly in the solid state. Fluorescence experiments demonstrated its aggregation-induced emission character and tunable solid-state fluorescence emission, and per-methylated FT (MeFT) also exhibited an intriguing excitation-wavelength-dependent (Ex-De) capability with different emission color-switching processes. Significantly, the activated powders of per-hydroxylated FT (OHFT) and MeFT with both nonporous and amorphous features displayed remarkable potential in constructing adsorptive separation materials for CO2 and CH4 capture, affording good selectivities of 31/1 for CO2/N2 (by OHFT) and 8/1 for CH4/CO2 (by MeFT), respectively. The discovery of FT will provide new perspectives in constructing novel fluorescent macrocycles and functional photo-responsive materials, unleashing new inspirations in molecular sorbents for gas adsorption and separation.

Study on the Tunable Fluorescence Emission Mechanism of Nitrogen-Doped Carbon Dots and Ion Sensing Potential Applications

Study on the Tunable Fluorescence Emission Mechanism of Nitrogen-Doped Carbon Dots and Ion Sensing Potential Applications

Sub-micron microparticles with tunable fluorescence emission obtained via co-self-assembly of amidoximed polymeric ligands and lanthanide ions.

Lanthanide coordinating polymeric microparticles have witnessed increasing research interests during the past decades due to their versatile morphology and tunable fluorescent properties. Herein, we have synthesized an amidoximed block copolymer containing aromatic backbone and pendent amidoxime as well as carboxyl groups, which has been employed as the ligand to sensitize the intrinsic fluorescence emission of lanthanide ions of Tb3+ and Eu3+. Furthermore, the lanthanide coordinating polymeric microparticles showing tunable green and red emission fluorescence have been prepared via the emulsion confinement co-self-assembly of amidoximed polymeric ligands with Tb3+ and Eu3+. It is found that both the fluorescence emission and sizes of obtained fluorescent microparticles can be easily modulated in a wide range by tuning concentration of polymers and lanthanide ions, as well as emulsion evaporation temperature. Thanks to their tunable sizes (250-900nm), fluorescence emission as well as presence of surface active functional groups, the present fluorescent microparticles would find potential applications in in-vitro detection, optical encoding and devices.

Solvents/photo/pillar[5]arene triple responsive morphology and luminescence transformation from an amphiphilic dicyanostilbene-functionalized thiophene

α-Cyanostilbene (CS) based organic luminescent materials with efficient electrical conductivity, aggregation-induced enhanced emission, and controllable multi-colour emission properties, have been aroused wide attention by scientists over the past few years. Self-assembly of CS-motif in aqueous media refers to an environment-friendly method for preparing luminescent materials. However, it is still challenging to control the intrinsic hydrophobic properties of the organic components in aqueous media. In this study, an amphiphilic dicyanostilbene-functionalized thiophene (ACSTP) derivative was synthesized. Z-ACSTP was identified to dissolve in different organic solvents, accompanied with strong and tunable fluorescence emission. However, when Z-ACSTP was dispersed in water, it was self-assembled into nanofibers, and the fluorescence was red shifted, accompanied with sharp decrease of intensity compared with that in DMSO. Furthermore, Z-form of ACSTP to its E-form under 365 nm irradiation led to the morphology transformation from nanofibers to nanosheets. Notably, upon addition of water-soluble pillar[5]arene (WP5), the nanofibers were transformed into fluorescent hollow particles due to the host–guest interactions between the pyridinium group and WP5 and the obtained fluorescent particles can be further applied in living cell imaging.

Quantum Dots Meet Enzymes: Hydrophobicity of Surface Ligands and Size Do Matter.

Colloidal quantum dots (QDs) are a class of representative fluorescent nanomaterials with tunable, bright, and sharp fluorescent emission, with promising biomedical applications. However, their effects on biological systems are not fully elucidated. In this work, we investigated the interactions between QDs with different surface ligands and different particle sizes and α-chymotrypsin (ChT) from the thermodynamic and kinetic perspectives. Enzymatic activity experiments demonstrated that the catalytic activity of ChT was strongly inhibited by QDs coated with dihydrolipoic acid (DHLA-QDs) with noncompetitive inhibitions, whereas the QDs coated with glutathione (GSH-QDs) had weak effects. Furthermore, kinetics studies showed that different particle sizes of DHLA-QDs all had high suppressive effects on the catalytic activity of ChT. It was found that DHLA-QDs with larger particle sizes had stronger inhibition effects because more ChT molecules were bound onto the surface of QDs. This work highlights the importance of hydrophobic ligands and particle sizes of QDs, which should be considered as the primary influencing factors in the assessment of biosafety. Meanwhile, the results herein can also inspire the design of nano inhibitors.

Hyperconjugation in light-switched intramolecular charge transfer of anthrapyridinium derivatives: New insight into molecular motion and fluorescent materials

Light-induced intramolecular charge transfer (ICT) is important in chemical and physical processes involving organic reactions and materials. However, because of the fast light-absorption rates and short excited state lifetime, charge-transfer separation and the resulting molecular motion in the ICT states are generally expected to be unidirectional and uncontrollable. Herein, an unexpected hyperconjugation derived light-switched ICT and tunable fluorescence emissions are described, and these can be rapidly and reversibly controlled in anthrapyridinium dyes by irradiation with light of different wavelengths such as 365 nm and 254 nm. Most importantly, the subtle differences between the dyes in terms of the σ–π (C–H and C–C) hyperconjugation between the alkyl chains and the pyridinium, which were confirmed from the 1H NMR spectra for the first time, and which was further proved to be the key factor affecting the light-induced ICT of the dyes.

Preparation of Ultrasmall AIE Nanoparticles with Tunable Molecular Packing via Freeze Assembly

Advances in the development of aggregation-induced emission luminogens (AIEgens) depend on understanding how the molecular packing affects their luminescent properties and on making nanoparticles (NPs) with desired sizes. Although reported strategies have advanced the field, rational control of molecular packing and efficient fabrication of AIEgen NPs sub-5.5 nm in diameter remain pressing issues. Here we report a "freeze assembly" strategy, in which the diameter of AIEgen NPs can be precisely tuned from ∼3 nm to hundreds of nanometers, and a molecular packing in kinetically trapped states that are not easily captured by conventional assembly methods can be obtained, leading to tunable fluorescence emissions. Therefore, this study provides a significant tool to fabricate organic luminescent nanomaterials with diameters smaller than 5 nm, which is of critical importance for biomedical applications; meanwhile, tuning molecular packing in nanoparticles displaying different fluorescence may help to shed new light on the mechanism of AIEgens.

Facile and Green Synthesis of Novel Fluorescent Carbon Quantum Dots and Their Silver Heterostructure: An In Vitro Anticancer Activity and Imaging on Colorectal Carcinoma.

Carbon dots (CQDs) have been widely investigated as prime candidates for developing a tumor theranostic platform due to their tunable fluorescence emission and excitation, high water solubility, good photostability, and biocompatibility. Among the CQDs, natural CQDs are an emerging class of nanomaterials in the carbon family. Herein, highly fluorescent carbon quantum dots (CQDs) were synthesized from orange juice using a one-step hydrothermal method and characterized by different techniques. After that, CQD/Ag heterostructures were synthesized by the reduction of silver salt, in particular silver nitrate (AgNO3) solution using sodium borohydride (NaBH4) in different ratios. The photostability and characterization of CQD/Ag heterostructures were investigated. At last, a comparative cellular toxicity measurement was done to select the superior CQD/Ag heterostructure in the human colorectal carcinoma (HCT 116) cell line along with the imaging property. The detailed cell death signaling was also observed in the HCT 116 cell line via the ROS-dependent mitochondrial-mediated pathway, where Akt (RAC-α serine/threonine-protein kinase) played a important role.

Semiconducting Polymer Dots for Point-of-Care Biosensing and In Vivo Bioimaging: A Concise Review.

In recent years, semiconducting polymer dots (Pdots) have attracted much attention due to their excellent photophysical properties and applicability, such as large absorption cross section, high brightness, tunable fluorescence emission, excellent photostability, good biocompatibility, facile modification and regulation. Therefore, Pdots have been widely used in various types of sensing and imaging in biological medicine. More importantly, the recent development of Pdots for point-of-care biosensing and in vivo imaging has emerged as a promising class of optical diagnostic technologies for clinical applications. In this review, we briefly outline strategies for the preparation and modification of Pdots and summarize the recent progress in the development of Pdots-based optical probes for analytical detection and biomedical imaging. Finally, challenges and future developments of Pdots for biomedical applications are given.