Fluorescent Films Research Articles

In‐situ controllable synthesis of carbon dots for patterned fluorescent wood films rapid fabrication strategy

AbstractFluorescent‐patterned materials are widely used in information storage and encryption. However, preparing a patterned fluorescent display on a matrix currently requires a time‐consuming (hours or even days) and complex multi‐step process. Herein, a rapid and mild technique developed for the in‐situ controllable synthesis of fluorescent nitrogen‐doped carbon dots (NCDs) on eco‐friendly transparent wood films (TEMPO‐oxidized carboxyl wood film [TOWF]) within a few minutes was developed. A wood skeleton was employed as the carbon precursor for NCD synthesis as well as the matrix for the uniform and controlled distribution of NCDs. Moreover, the in‐situ synthesis mechanism for preparing NCDs in TOWF was proposed. The resulting fluorescent wood films have excellent tensile strength (310.00 ± 15.57 MPa), high transmittance (76.2%), high haze (95.0%), UV‐blocking properties in the full ultraviolet (UV) range, and fluorescent performance that can be modified by changing the heating parameters. Fluorescent patterning was simply achieved by regulating the in‐situ NCD synthesis regions, and the fluorescent patterns were formed within 10 s. These fluorescent‐patterned wood films can effectively store and encrypt information, and they can interact with external information through a transparent matrix. This work provides a green and efficient strategy for fabricating fluorescent information storage and encryption materials.

Fluorescent carbon dots doped with nitrogen for rapid detection of Fe (III) and preparation of fluorescent films for optoelectronic devices

The paper presents a green and easily prepared water-soluble fluorescent nitrogen doped carbon dots (NCDs) synthesized by one-step hydrothermal process. The NCDs displays brilliant blue fluorescence excited by UV light, with excellent water solubility, and a quantum yield of 15.7 %. The fluorescence intensity of NCDs remains unchanged after 48 h of exposure to ultraviolet light, exhibiting good photostability. Moreover, the ion sensing characteristics of these NCDs have been explored for more than a dozen anions and cations. The result reflects that this fluorescent CDs exhibits excellent sensitivity and selectivity for Fe3+ within a range spanning of 40 ∼ 500 μΜ with a limit of detection down to 0.22 μΜ. The principle of sensor sensing is likely related to the formation of the internal filtering effect (IFE), which leads to a decline in the fluorescence intensity of NCDs in aqueous solutions containing Fe3+. Due to the excellent water solubility, good photostability and high yield of NCDs, the application of prepared NCDs/polyvinyl alcohol (PVA) as fluorescent materials for white LED devices was explored. The prepared NCDs/PVA (NCP) composite film can also exhibit bright blue light under 365 nm excitation, indicating good application prospects in the area of white LED devices and agricultural films.

Eco-Friendly Electrophoretic Deposition of Fluorescent Nanocomposite Films in an Aqueous Dispersion of Hydrophilized Core/Shell CuInS2/ZnS Quantum Dots for Optoelectronic Applications.

Low-toxic and efficient fluorescent core-shell CuInS2/ZnS (CIS/ZnS) quantum dots (QDs) are good candidates for optoelectronic device applications. They are synthesized in a hydrophobic environment, while large amounts of organic solvents used in the preparation of fluorescent films have significant problems on environmental load and human health. CIS/ZnS QDs hydrophilized by adsorbing 3-mercaptopropionic acid on their surfaces can be used in the aqueous film fabrication process. In this work, the aqueous electrophoretic deposition (EPD) of the hydrophilized QDs with silicone-modified acrylic resin nanoparticles was performed to fabricate fluorescent nanocomposite films. The hydrophilized QDs and resin nanoparticles were simultaneously dispersed in basic aqueous solutions due to electrostatic repulsion resulting from their negatively charged surfaces. Transparent films were obtained on a transparent conductive substrate at the anode side by the EPD. They showed yellow fluorescence of the QDs. The thickness increased with increasing the deposition time; however, hemispherical holes attributed to oxygen gas generated by water electrolysis were observed at the longer time. The electron microscopy revealed that the films were densely and homogeneously deposited. The QDs were dispersed around the resin nanoparticles without aggregation. The fluorescence (FL) quantum yield was 43%. The optical absorption peak and FL intensity of the QDs increased accompanied by the film growth. The nanocomposite film showed good heat resistance at 80-120 °C for 5 h; therefore, the prepared films have feasibility in white light-emitting diode (LED) applications. A lightening device structured with the obtained EPD film placed on a blue LED successfully emitted white light. In addition, the flexibility of the nanocomposite film was demonstrated. The aqueous EPD method would be one of the suitable methods for the industrial production of fluorescent QD films. This technique can be applied to other hydrophilic fluorescent QDs with charged surfaces. Realization of various fluorescent QD films would expand the application possibilities.

A Nanofilm-Based Fluorescent Sensor toward Highly Efficient Detection of Ethephon.

Ethephon (ETH) is widely used to promote fruit ripening and improve fruit quality. However, improper use is harmful to human health and to the environmental safety. Therefore, development of the techniques for on-site and at real-time monitoring of ETH is of importance for its safe use. In this work, we developed a nanofilm-based fluorescence film sensor (FFS) and realized highly efficient detection of ETH in vapor phase, where the detection limit (DL) is <0.2 ppb, the response time is less than 10 s, and the interference is almost free. The unusual sensing performance of the sensor was ascribed to the specific binding of the nanofilm to ETH and to its great porosity, which enables efficient adlayer mass transfer, a requirement for high signal-to-noise ratio. Moreover, visualization-based qualitative sensing is also realized. The nanofilm, a key component of the sensor, was prepared at the humid air/DMSO interface. The building blocks used were a specially designed fluorescent o-carborane derivative (CB-2CHO) and a cross-linker BTN possessing three acylhydrazine groups. The nanofilm as prepared is flexible, uniform, thickness tunable, and photochemically super stable. We believe our effort not only addresses the challenging issue of on-site and at real-time detection of ETH but also provides another route for developing new FFSs via sensing film innovation.

Aiegen-based fluorescent polymer films with tunable Janus luminescence and structural color

Fluorescent polymer films (FPFs) doped with aggregation-induced emission luminogens (AIEgens) have attracted great attention of scientists for their potential to solve the aggregation-caused quenching effect of traditional fluorescent molecules. Here, to rich the information and enhance the function of FPFs, AIEgens (DCDPP-2TPA) doped FPF was placed in the middle of two different inverse opal photonic crystals (IOPCs), whose photonic band gaps matched with the FPF's red and blue region respectively. Owing to the regulation effect of the IOPCs, tunable Janus luminescence and structural color depending on the viewing angle were achieved. Through designing complex patterns in FPFs, encrypted information can be decoded simply by ultraviolet light. More importantly, the decoded information displays different luminescent colors on each side, and the luminescence on each side is tunable with viewing angles. The “sandwich” structure can be used in most daily environments. Its unique property of variable Janus emissions and structural colors endow the structure with highly safe anti-counterfeiting performance.

Amine vapor-responsive ratiometric sensing tag based on HPTS/TPB-PVA fluorescent film for visual determination of fish freshness

In this study, amine vapor-sensitive films with ratiometric fluorescence attributes were developed. The pH-sensitive fluorescein 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (HPTS) and its tetraphenylethylene derivative (TPB) were selected as ratiometric indicators and incorporated into a polyvinyl alcohol (PVA) matrix to produce HPTS/TPB-PVA films. The films responded well to amine vapors, and the interference of aromatic vapors did not substantially affect the fluorescence signals of the films. Under UV light at a wavelength of 365 nm, the fluorescence of the films changed from dark pink to light pink and finally to yellow when the freshness of the fish was visually checked during storage. In addition, the color difference values of the films showed a positive correlation with the total volatile basic nitrogen (TVB-N), ranging from 12.7 to 24.8 mg/100 g at 25 °C and 8.4 to 25.6 mg/100 g at 4 °C, respectively. This indicates that fluorescent films have good potential for quantifying fish freshness in the near future when connected to an automatic data processing system based on color differences.

A flavonol-labelled cellulose fluorescent probe combined with composite fluorescent film imaging and smartphone technology for the detection of Fe3+

Fe3+ is one of the most widely distributed and abundant elements on earth. Realizing efficient and real-time monitoring of Fe3+ is of great significance for the natural environment and the health of living organisms. In this paper, a flavonol-labelled cellulose-based fluorescent probe (ACHM) was synthesized by using dialdehyde cellulose (DAC) as the backbone and combining with flavonol derivatives (AHM - 1). The mechanism of recognizing Fe3+ was verified by characterizing the structure of ACHM by NMR, HRMS (High Resolution Mass Spectrometry), FTIR (Fourier Transform Infrared Spectroscopy), XRD (X-ray Diffraction), TG (Thermogravimetry) and SEM (Scanning Electron Microscopy). The H2O solution of the probe ACHM showed good fluorescence properties. It has quenching fluorescence properties for Fe3+, with a low limit of detection (LOD) of 0.10 μM and a fast response time of only 20 s. In addition, in order to expand the application range of the probe, ACHM was prepared as a fluorescent composite film with an average tensile strength of 32.9 MPa and an average elongation at break of 3.39 %. It shows its superiority in mechanical properties. The probe also demonstrated its practical application value for detecting Fe3+ in smartphone imaging applications.

Real-time detection of TNT analogues in water using fluorescent dendrimer films

Thin fluorescent dendrimer films detect 2,4,6-trinitrotoluene (TNT) and its analogues dissolved in water.

Robust lanthanide MOFs as multifunctional luminescent sensors for intelligent visualization monitoring of MEAA and texture code anti-counterfeiting applications

Ln-MOFs were designed for anti-counterfeiting labels by using texture codes. Moreover, three visual probes based on 1-Eu for MEAA detection are fluorescent films, RGB intelligent detection sensor platforms, and portable logic detectors.

Bay-substituted octaazaperopyrenedioxides as solid-state emitters for strong light-matter coupling

Organic solid-state emitters based on a twisted octaazaperopyrenedioxide core can be processed from solution into smooth and highly fluorescent thin films and are integrated directly into optical microcavities for strong light-matter coupling.

Modeling and admittance recursive simulation of anti-reflective coatings for photothermal conversion: synergy between subwavelength structures and gradient refractive index layers.

In the field of photothermal conversion, light-absorbing layers show limitations such as low solar energy utilization and excessive surface reflection. This paper proposes a new anti-reflective coating consisting of a gradient-doped fluorescent glass film covering a subwavelength structural layer for photothermal conversion. Its transmittance was simulated using equivalent medium theory and the admittance recursion method. The subwavelength structure provides a refractive index gradient, and its shape solves the problem of the sharp decrease in transmittance at high angles of incidence. Subsequently, we adjust the material parameters of the gradient refractive layers and control the thickness of each layer to minimize interlayer Fresnel reflections. Finally, the efficient light-trapping ability of the model was verified by calculating and comparing the transmittances of the optimized model and bare glass. Notably, within the visible spectrum, our model achieves an average transmittance of over 95% across wavelength and angle ranges, effectively suppressing surface reflections. At a larger light incident angle, the transmittance increases by 29.7%, and the minimum angle transmittance reaches 92.7%. This study proposes an innovative method to enhance the performance of transmission layers in photothermal conversion devices.

Preparation and Properties of Spinach-based Multicolor Luminescent Carbon Dots and Chiral Fluorescent Films

Preparation and Properties of Spinach-based Multicolor Luminescent Carbon Dots and Chiral Fluorescent Films

Self-Assembled and Polymerized Hierarchical Nanostructure Films of Cyanostilbene-Based Reactive AIEgens for Smart Chemosensors.

For the development of acid-responsive advanced fluorescent films with a 2D nanostructure, a pyridyl cyanostilbene-based AIEgen (PCRM) is newly synthesized. The synthesized PCRM exhibits aggregation-induced emission (AIE) and responds reversibly to acid and base stimuli. To fabricate the nanoporous polymer-stabilized film, PCRM and 4-(octyloxy)benzoic acid (8OB) are complexed in a 1:1 ratio through hydrogen bonding. The PCRM-8OB complex with a smectic mesophase is uniaxially oriented at first and photopolymerized with a crosslinker. By subsequently removing 8OB in an alkaline solution, nanopores are generated in the self-assembled and polymerized hierarchical 2D nanostructure film. The prepared nanoporous fluorescent films exhibit not only the reversible response to acid and base stimuli but also mechanical and chemical robustness. Since the nanoporous fluorescent films have different sensitivities to trifluoroacetic acid (TFA) depending on the molecular orientation in the film, advanced acid vapor sensors that can display the risk level according to the concentration of TFA are demonstrated. Reactive AIEgens-based hierarchical nanostructure films with nanopores fabricated by a subsequent process of self-assembly, polymerization, and etching can open a new door for the development of advanced chemosensors.

Alginate-modified surfactants functionalized metal-organic framework-based fluorescent film sensors for detection and adsorption of volatile aldehydes in water

Volatile aldehydes have an adverse impact on both human health and the environment, therefore, a fast, straightforward, highly accurate detection technique for the simultaneous detection and removal of several aldehydes is eagerly anticipated. Herein, novel APGF@ZIF-8 and APOF@ZIF-8 sensing materials were developed by coating fluorescent alginate-modified surfactants (APGF and APOF) into the ZIF-8 MOFs to produce quite porous fluorescent sensors (SBET up to 1519 m2/g). The detection capacity of the prepared sensors for benzaldehyde, glyoxal, formaldehyde, and acetaldehyde has been examined. The detection mechanism was suggested as hydrogen bonding formation between the sensors and volatile aldehydes as confirmed by Gaussian calculations. All the fluorescence spectra of aldehydes display remarkable linear detection relationships in the range of 0.05–200 μM with the limits of detection (LOD) values in the range of 0.001–0.18 μM (0.106–10.44 ppb). These sensors were utilized successfully to detect multiple volatile aldehydes in river water samples with satisfactory recoveries of 96–107 %. Interestingly, fluorescent APGF@ZIF-8/CS and APOF@ZIF-8/CS films as portable disposable removal techniques for benzaldehyde, glyoxal, formaldehyde, and acetaldehyde from water were fabricated. APOF@ZIF-8/CS exhibited an excellent formaldehyde adsorption capacity of 58.30 mg/g and an adsorption removal efficiency of 93.5 %. The adsorption process of biosorbent on various aldehydes was fitted by Freundlich adsorption isotherm. The adsorption kinetics followed Pseudo-second-order kinetic model.

Carbon dots-based fluorescent films to act as a potential antioxidant agent and pH ratiometric sensor for skin applications

The wound healing process is accompanied by changes in pH values. Monitoring this physicochemical parameter can indicate the effectiveness of the applied treatment and act as early identification of wound infection. This study focuses on the development of a fluorescent film-based polyvinyl alcohol (PVA) and carbon dots (CDs) derived from lemon bagasse (CD-L) and ortho-phenylenediamine (CD-oPD) named to act as antioxidants and potential ratiometric fluorescent pH sensors, in wound applications. The I460/I550 intensity ratio, as a function of pH value for the dual-system CDs prepared from the mixture of CD-L and CD-oPD, named CD-L/oPD, was investigated. The fit corresponded to a sigmoidal function in the pH range of 5–10, with a relationship having a r2 = 0.992. The variation in the values of the I460/I550 ratio allows for the visualization of the color change from yellowish-green to green with increasing pH. Through a simulated ex vivo pig skin model, it was possible to note that the films prepared from mixed of the CD-L and CD-oPD carbon dots incorporated in a matrix PVA named CD-L/oPD-F was more efficient at visually discriminating color in relation to changes in pH than the films prepared from both individual CD-L (CD-L-F) and CD-oPD (CD-oPD-F) carbon dots. CD-L and CD-oPD demonstrated antioxidant capacity against reactive oxygen species (ROS). The IC50 values for CD-L and CD-oPD were 56.7 and 39.5 μg mL−1 in the DPPH● inhibition assay, and 25.1 and 63.4 μg mL−1 in the HOCl scavenging one, respectively. MTT viability assays using human non-tumoral skin fibroblast (HFF-1) cell showed a cell survival rate of over 80% for both CDs up to a concentration of 1,000 μg mL−1. Finally, the developed films can act in a bifunctional way, by monitoring healing through pH changes and by acting as an antioxidant agent in the treatment of wounds.

A sensitive fluorometric-colorimetric dual-mode intelligent sensing platform for the detection of formaldehyde

Excess formaldehyde (FA) is a strong carcinogen, so the development of a rapid visualized and portable formaldehyde detection platform is of great research importance. A multi-color fluorescence sensing system constituted of model compound (NAHN) and red-emitting InP/ZnS QDs was constructed herein, which can simultaneously realize fluorometric-colorimetric dual-mode sensing when exposed to FA environment. Its preparation process was simplified, the detection process was green, and the limits of detection (LOD) were 0.623 μM and 0.791 μM, respectively. The high recoveries of FA in actual water samples indicated that the sensor had broad application prospects. The prepared fluorescent film can be utilized for rapid visual simulation analysis of FA on the surface of various fruits and vegetables. In addition, a serial logic gate was designed to quickly semi-quantitatively assess FA concentration, which promoted the realization of on-site intelligent evaluation of FA.

A multifunctional optoelectronic device based on 2D material with wide bandgap

Low-dimensional materials exhibit unique quantum confinement effects and morphologies as a result of their nanoscale size in one or more dimensions, making them exhibit distinctive physical properties compared to bulk counterparts. Among all low-dimensional materials, due to their atomic level thickness, two-dimensional materials possess extremely large shape anisotropy and consequently are speculated to have large optically anisotropic absorption. In this work, we demonstrate an optoelectronic device based on the combination of two-dimensional material and carbon dot with wide bandgap. High-efficient luminescence of carbon dot and extremely large shape anisotropy (>1500) of two-dimensional material with the wide bandgap of >4 eV cooperatively endow the optoelectronic device with multi-functions of optically anisotropic blue-light emission, visible light modulation, wavelength-dependent ultraviolet-light detection as well as blue fluorescent film assemble. This research opens new avenues for constructing multi-function-integrated optoelectronic devices via the combination of nanomaterials with different dimensions.

Perylene Diimide Based Fluorescent Sensors for Drug Simulant Detection: The Effect of Alkyl-Chain Branching on Film Morphology, Exciton Diffusion, Vapor Diffusion, and Sensing Response.

Luminescence-based sensing has been demonstrated to be a powerful method for rapid trace detection of chemical vapors (analytes). Analyte diffusion has been shown to be the critical factor for real-time luminescence-based detection of explosive analytes via photoinduced electron transfer in amorphous films of conjugated polymers and dendrimers. However, similar studies to determine the critical factors for sensing have not been performed on materials that employ photoinduced hole transfer (PHT) to detect low electron affinity analytes such as illicit drugs. Nor have such studies been performed on semicrystalline sensing films. We have developed a family of perylene diimide-based sensing materials capable of undergoing PHT with amine-group containing analytes. It was found that the choice of branched alkyl chain [1-hexylheptyl (PHH), 2-hexyloctyl (PHO), or 2,2-dihexyloctyl (PDHO)] attached to the nitrogen atoms of the imide moiety strongly affected the solution-processed film morphology. PHH and PHO were found to contain crystalline phases, whereas PDHO was essentially amorphous. The degree of crystallinity strongly influenced exciton diffusion, with PHH and PHO exhibiting exciton diffusion coefficients that were 20× and 10× greater than the value of the amorphous PDHO. The degree of film crystallinity was also found to be critical when the films were applied to detect N-methylphenethylamine (MPEA), a simulant of methamphetamine. While PHH had the largest exciton diffusion coefficient [(1.0 ± 0.2) × 10-2 cm2 s-1] and analyte uptake (12.3 ± 1.8 ng) it showed the smallest quenching efficiency (2.6% ng-1). In contrast, PHO, which sorbed the least analyte (6.1 ± 0.4 ng) of the three compounds, had the largest quenching efficiency (7.1% ng-1) due to its molecular packing and hence exciton diffusion coefficient [(4.5 ± 1.4) × 10-3 cm2 s-1] not being affected by sorption of the analyte. These results show that when applying fluorescent films in practical detection scenarios there is a potential trade-off between a high exciton diffusion constant and analyte diffusion for semicrystalline sensing materials and that a high exciton diffusion coefficient in an as-cast film does not necessarily translate into a more efficient fluorescent quenching. The results also show that sensing materials that form semicrystalline films, whose packing is not disrupted by analyte diffusion, provide a route for overcoming these effects and achieving high sensitivity.

Preparation of multicolor carbon quantum dots by hydrothermal method and their functionalization applications

Carbon quantum dots (CQDs) have become a popular research topic because of their many unique virtues, especially the significance of tunable photoluminescence properties. However, the synthesis of multicolor CQDs is still at an exploratory stage, and there are many dilemmas that have not yet been well resolved, such as long-wavelength emission and solid-state luminescence. Here, we selected suitable carbon and dopant sources as precursors for the synthesis of CQDs through the rational design of the experiments in an aqueous system, and the as-prepared CQDs possessed blue, green, yellow and red emissions, with optimal emissions of approximately 475 nm, 530 nm, 580 nm, and 645 nm, respectively. Furthermore, the corresponding PLQYs were 30.13 %, 36.84 %, 39.16 % and 21.36 %, respectively. It was found that the redshift of the emission wavelengths can be attributed to the synergistic effect of the increase in the sp2 conjugate size and the surface states. To conquer the aggregation caused quenching (ACQ) of CQDs and realize the solid-state luminescence of CQDs, we successfully prepared solid-state fluorescent films and solid-state phosphors. Finally, multicolor CQDs were successfully applied to prepare monochromatic and white light-emitting diodes (WLEDs). The adopted green synthesis technology can provide a good technical support for the future development of CQDs synthesis.

Bioinspired thermadapt shape-memory polymer with light-induced reversible fluorescence for rewritable 2D/3D-encoding information carriers

Fluorescent materials have attracted widespread attention for information encryption owing to their stimuli-responsive color-shifting. However, the 2D encoding of fluorescent images poses a risk of information leakage. Herein, inspired by the mimic octopus capable of camouflage by changing colors and shapes, we develop a thermadapt shape-memory fluorescent film (TSFF) for integrating 2D/3D encoding in one system. The TSFF is based on anthracene group with reversible photo-cross-linking and poly (ethylene-co-vinyl acetate) network with thermadapt shape-memory properties. The reversible photo-cross-linking of anthracene is accompanied by repeatable fluorescence-shifting and enables rewritable 2D encoding. Meanwhile, the thermadapt shape-memory properties not only enables the reconfiguration of the permanent shape for creating and erasing 3D patterns, i.e., rewritable 3D information, but also facilitates recoverable shape programming for 3D encoding. This rewritable 2D/3D encoding strategy can enhance information security because only designated inspectors can decode the information by providing sequential heating for shape recovery and UV exposure. Overall, TSFF capable of rewritable 2D/3D encoding will inspire the design of smart materials for high-security information carriers.