Fluorescent Thin Films Research Articles

Red-emitting copper nanoclusters for ultrasensitive and selective detection of creatinine and its application in portable smartphone-based paper strips and polymer thin film

In this work, a quantitative paper-based sensor integrated with smartphone-application was developed using poly(sodium 4-styrenesulfonate) stabilized copper nanoclusters (PSS-CuNCs) as a fluorescence probe to detect creatinine (CRN). The surface morphology and optical properties of PSS-CuNCs were verified using UV–vis absorption, zeta-potential, photoluminescence, high resolution transmission electron microscopy (HR-TEM) and Fourier-transform infrared (FI-IR) and X-ray photoelectron (XPS) spectroscopy. PSS-CuNCs exhibited strong red fluorescence with the emission peak centered at 654 nm upon excitation at 390 nm. PSS-CuNCs was also used to determine CRN because of their excellent fluorescence properties. The fluorescence of PSS-CuNCs was quenched significantly by adding different concentrations of CRN, which mainly originated from the formation of ground state complexation. The PSS-CuNCs probe showed high sensitivity with a low limit of detection (LOD) of 2.48 nM and high selectivity even in the presence of other interfering analytes. This assay was also used to measure CRN in real samples. Additionally, test paper-based assay has been developed to detect CRN using smartphones. The developed assay provides a reliable, cost-effective, sensitive and portable on-site method to measure CRN levels by utilizing fluorescence color changes. Incorporation of PSS-CuNCs into poly(vinyl alcohol) resulted in the formation of fluorescent transparent polymer thin films with high photostability.

Enhanced Quantum Efficiency of Near-IR Perovskite Light Emitting Diodes Via Dual Interfacial Modification

Near-infrared (NIR) light-emitting diodes play a crucial role in a wide range of applications, including sensors, night vision displays, security systems, medicine, spectroscopy, and military applications. The potential for high-performance NIR perovskite light-emitting diodes (NIR-PeLEDs) has been highlighted with the impressive advancement of fluorescent perovskite thin films. These PeLEDs exhibit promising features such as a tunable band gap, high color purity, and low non-radiative recombination rates. Despite these advantages, the current state-of-the-art NIR-PeLEDs faces challenges primarily related to poor film quality and increased defect states, leading to limitations in external quantum efficiency (EQE) and operational stability. In addressing these issues, we present a novel dual interfacial modification approach involving the incorporation of fluorinated phenethylammonium iodide (F-PEAI), a bulky organic cation, at both the bottom and top interfaces of perovskite emitting films. The modified interfaces result in perovskite films with a smoother surface morphology, complete coverage, and high crystallinity, leading to a red-shifted fluorescence band extending toward 800 nm. Furthermore, the introduction of F-PEAI facilitates the formation of compact and fine grains in perovskite films, contributing to an enhanced photoluminescence quantum yield (PLQY). Consequently, NIR-PeLEDs modified with F-PEAI demonstrate improved EQE values coupled with enhanced operational stability. The combination of electrical, optical, and physical analyses of both films and devices underscores the effectiveness of the dual interface modification in developing efficient NIR perovskite LEDs suitable for practical applications.

Preparation of dispersible carbon nitride powder and fabrication of its thin films by wet-process

To establish a low-cost and environment-friendly method for producing blue fluorescent materials and their thin films, we investigated the conditions for synthesizing graphitic carbon nitride (g-C3N4) powder from urea and melamine. We found that urea can be used to synthesize g-C3N4 at lower annealing temperatures than melamine. The synthesized g-C3N4 powder showed good dispersibility in deionized water and methanol, and it was found that relatively uniform g-C3N4 thin films could be obtained by low-speed spin-coating, especially with highly volatile methanol dispersions. These results indicate that blue fluorescent thin films can be fabricated using a wet process at room temperature.

Two-Coordinate Thermally Activated Delayed Fluorescence Coinage Metal Complexes: Molecular Design, Photophysical Characters, and Device Application.

Since the emergence of the first green light emission from a fluorescent thin-film organic light emitting diode (OLED) in the mid-1980s, a global consumer market for OLED displays has flourished over the past few decades. This growth can primarily be attributed to the development of noble metal phosphorescent emitters that facilitated remarkable gains in electrical conversion efficiency, a broadened color gamut, and vibrant image quality for OLED displays. Despite these achievements, the limited abundance of noble metals in the Earth's crust has spurred ongoing efforts to discover cost-effective electroluminescent materials. One particularly promising avenue is the exploration of thermally activated delayed fluorescence (TADF), a mechanism with the potential to fully harness excitons in OLEDs. Recently, investigations have unveiled TADF in a series of two-coordinate coinage metal (Cu, Ag, and Au) complexes. These organometallic TADF materials exhibit distinctive behavior in comparison to their organic counterparts. They offer benefits such as tunable emissive colors, short TADF emission lifetimes, high luminescent quantum yields, and reasonable stability. Impressively, both vacuum-deposited and solution-processed OLEDs incorporating these materials have achieved outstanding performance. This review encompasses various facets on two-coordinate TADF coinage metal complexes, including molecular design, photophysical characterizations, elucidation of structure-property relationships, and OLED applications.

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.

Detection of refractive index and imperfection in thin film transparent polymer by back focal plane imaging

Emission patterns from molecules at interfaces encode many details about their local environment and their axial position, along the microscope’s optical axis. We introduce an advanced approach that synergizes back focal plane (BFP) imaging with innovative ‘smart’ surfaces make surface imaging more qualitative, more reliable, and more robust. Our method is particularly focused on accurately measuring the refractive index (RI) of transparent thin films and their imperfections close to the interfaces. Our technique utilizes a ‘smart’ surface, which features a uniform fluorescent thin film of about 4 nm thickness together with back-focal plane (BFP) imaging. We manage to detect bubbles or other imperfection in 100 nm thin film of polymer with RI of 1.34.

Resonant Critical Coupling of Surface Lattice Resonances with a Fluorescent Absorptive Thin Film

Resonant Critical Coupling of Surface Lattice Resonances with a Fluorescent Absorptive Thin Film

Inducing Circularly Polarized Luminescence by Confined Synthesis of Ultrasmall Chiral Carbon Nanodot Arrays in Pyrene-Based MOF Thin Film.

Combining the features of the host-guest system and chirality is an efficient strategy to achieve circularly polarized luminescence (CPL). Herein, well-defined chiral carbon nanodot (chirCND) arrays were confined-synthesized by low-temperature calcination of a chiral amino acid loaded metal-organic framework (MOF) to induce high CPL. An achiral porous pyrene-based MOF NU-1000 thin film as the host template was prepared by a liquid-phase epitaxial layer-by-layer fashion, and chiral amino acids as the carbon sources could be confined in the porous MOF and carbonized to homogeneous and ultrasmall chirCND arrays, resulting in a chirCNDs@NU-1000 thin film (l-CNDsx@NU-1000; x = l-cysteine (cys), l-serine, l-histidine, l-glutamic acid, and l-pyroglutamic acid). The results show the pristine chirCNDs by directly carbonizing chiral amino acids hardly endow them with a CPL property. By contrast, benefiting from the arrayed confinement and coordination interaction between chirCNDs and NU-1000, the chirality transfer on the excited state of chirCNDs@NU-1000 is enabled, leading to strong CPL performance (a high luminescence dissymmetry factor glum of l-CNDscys@NU-1000 thin film reached 1.74 × 10-2). This study of chirCNDs encapsulated in fluorescent MOF thin films provides a strategy for developing uniform chiral carbon nanoarrays and offers chiral host-guest thin-film materials for optical applications.

Molecular Thin Films Enable the Synthesis and Screening of Nanoparticle Megalibraries Containing Millions of Catalysts.

Megalibraries are centimeter-scale chips containing millions of materials synthesized in parallel using scanning probe lithography. As such, they stand to accelerate how materials are discovered for applications spanning catalysis, optics, and more. However, a long-standing challenge is the availability of substrates compatible with megalibrary synthesis, which limits the structural and functional design space that can be explored. To address this challenge, thermally removable polystyrene films were developed as universal substrate coatings that decouple lithography-enabled nanoparticle synthesis from the underlying substrate chemistry, thus providing consistent lithography parameters on diverse substrates. Multi-spray inking of the scanning probe arrays with polymer solutions containing metal salts allows patterning of >56 million nanoreactors designed to vary in composition and size. These are subsequently converted to inorganic nanoparticles via reductive thermal annealing, which also removes the polystyrene to deposit the megalibrary. Megalibraries with mono-, bi-, and trimetallic materials were synthesized, and nanoparticle size was controlled between 5 and 35 nm by modulating the lithography speed. Importantly, the polystyrene coating can be used on conventional substrates like Si/SiOx, as well as substrates typically more difficult to pattern on, such as glassy carbon, diamond, TiO2, BN, W, or SiC. Finally, high-throughput materials discovery is performed in the context of photocatalytic degradation of organic pollutants using Au-Pd-Cu nanoparticle megalibraries on TiO2 substrates with 2,250,000 unique composition/size combinations. The megalibrary was screened within 1 h by developing fluorescent thin-film coatings on top of the megalibrary as proxies for catalytic turnover, revealing Au0.53Pd0.38Cu0.09-TiO2 as the most active photocatalyst composition.

Bright yellow fluorescent nitrogen and boron doped-CNPs based turn “off–on” probe for highly sensitive and selective detection of glyphosate and hypochlorite

In the present work, water-soluble fluorescent nitrogen/boron-doped carbon nano particles (N/B-CNPs) were prepared using o-phenylenediamine and boric acid precursors by a simple one step hydrothermal (HT) method. High Resolution Transmission Electron Microscope (HR-TEM) analysis showed that the N/B-CNPs are spherical in shape with an average size of ∼ 15 nm. The functional and structural composition of N/B-CNPs were confirmed by Fourier Transform Infrared (FTIR), Raman and Nuclear Magnetic Resonance (NMR) spectral studies. N/B-CNPs exhibited excellent photophysical property and photostability at different physiological conditions. N/B-CNPs showed bright yellow fluorescence at 566 nm upon excitation at 400 nm. N/B-CNPs were utilized as a fluorometric probe towards the simultaneous detection of glyphosate and hypochlorite. The fluorescence intensity of N/B-CNPs was selectively quenched in the presence of glyphosate (turn-off) and quenched emission intensity was restored in the presence of hypochlorite (turn-on). The fluorescence quenching mechanism was further ascertained using Stern-Volmer and time resolved fluorescence analysis. The detection probe showed a linear response for glyphosate over the concentrations range of 5.00 to 85.00 µM, with a limit of detection value of 0.088 µM. While in the case of hypochlorite the turn-on assay exhibited good linearity over the range of 5.00 to 50.00 µM with limit of detection as low as 0.12 nM. The N/B-CNPs turn-off/turn-on fluorometric assay exhibited excellent sensitivity and selectivity towards glyphosate and hypochlorite, even in the presence of other interference ions. The practical applicability of the proposed assay was demonstrated by fabricating a paper strip-based sensor and fluorescent thin film. Furthermore, the in vivo toxicity of the N/B-CNPs was evaluated in plant by performing dosage dependent assay.

Polyvinyl Butyral Polymeric Host Material-Based Fluorescent Thin Films to Achieve Highly Efficient Red and Green Colour Conversion for Advanced Next-Generation Displays.

Rare-earth element-free fluorescent materials are eco-friendlier than other traditional fluorescent precursors, such as quantum dots and phosphors. In this study, we explore a simple and facile solution-based technique to prepare fluorescent films, which are highly stable under ordinary room conditions and show hydrophobic behaviour. The proposed hybrid material was designed with hybrid composites that use polyvinyl butyral (PVB) as a host doped with organic dyes. The red and green fluorescent films exhibited quantum yields of 89% and 80%, respectively, and both are very uniform in thickness and water resistant. Additionally, PVB was further compared with another polymeric host, such as polyvinylpyrrolidone (PVP), to evaluate their binding ability and encapsulation behaviour. Next, the effect of PVB on the optical and chemical properties of the fluorescent materials was studied using UV spectroscopy and Fourier transform infrared spectroscopy. The analysis revealed that no new bond was formed between the host material and fluorescent precursor during the process, with intermolecular forces being present between different molecules. Moreover, the thickness of the fluorescent film and quantum yield relation were evaluated. Finally, the hydrophobic nature, strong binding ability, and optical enhancement by PVB provide a powerful tool for fabricating a highly efficient fluorescent film with enhanced stability in an external environment based on its promising encapsulation properties. These efficient fluorescent films have a bright potential in colour conversion for next-generation display applications.

Investigation into Red Emission and Its Applications: Solvatochromic N-Doped Red Emissive Carbon Dots with Solvent Polarity Sensing and Solid-State Fluorescent Nanocomposite Thin Films.

In this work, a NIR emitting dye, p-toluenesulfonate (IR-813) was explored as a model precursor to develop red emissive carbon dots (813-CD) with solvatochromic behavior with a red-shift observed with increasing solvent polarity. The 813-CDs produced had emission peaks at 610 and 698 nm, respectively, in water with blue shifts of emission as solvent polarity decreased. Subsequently, 813-CD was synthesized with increasing nitrogen content with polyethyleneimine (PEI) to elucidate the change in band gap energy. With increased nitrogen content, the CDs produced emissions as far as 776 nm. Additionally, a CD nanocomposite polyvinylpyrrolidone (PVP) film was synthesized to assess the phenomenon of solid-state fluorescence. Furthermore, the CDs were found to have electrochemical properties to be used as an additive doping agent for PVP film coatings.

Multifunctional Fluorescent Main-Chain Charged Polyelectrolytes Synthesized by Cascade C-H Activation/Annulation Polymerizations.

Fluorescent polyelectrolytes have attracted enormous attention as functional polymer materials. In contrast with the widely studied conjugated polyelectrolytes with ionic groups in side chains, fluorescent main-chain charged polyelectrolytes (MCCPs) have rarely been explored due to the large synthetic difficulty. Herein, we develop a facile and atom-economical N-heterocyclic carbene-directed cascade C-H activation/annulation polymerization strategy that can transform readily available imidazolium substrates and internal diynes into multifunctional fluorescent MCCPs with complex structures and high molecular weights (absolute Mn up to 135 600) in nearly quantitative yields. The presence of multisubstituted polycyclic N-heteroaromatic cations in polymer backbones endow the obtained MCCPs with excellent solution processability, high thermal stability, and dual-state efficient fluorescence in both solution and aggregate states. Benefiting from the strong electron-withdrawing capability of the cationic heterocycles in main chains, multicolored aggregate-state fluorescence can be readily achieved by modifying the substituents around the cationic ring-fused core. Taking advantage of the good photosensitivity of the fluorescent MCCP thin films, multiscale and high-resolution fluorescent photopatterns with different colors can be facilely prepared with potential applications in optical display devices and anticounterfeiting systems. Moreover, the strong electrostatic interactions of these cationic MCCPs with anionic polyelectrolytes enable them to form multicolored fluorescent interfacial polyelectrolyte complexation microfibers with directly visualized internal structures. Such flexible microfibers can be further made into diversified forms of fiber-based macroscopic patterns or painting.

Portable and non-invasive fluorescent thin films from photocatalytically active carbon dots for selective and trace-level detection of picric acid

Multifunctional N, S and P-doped CDs derived from C. thevetia flowers are used in a PVDF-based portable recyclable thin film fluorescent probe for selective trace level detection of picric acid and for the environmental remediation of azo dyes, acting as a potential solar photocatalytic material.

A UOF based on a cyclotriphosphazene skeleton: fluorescence sensing of different substituted aldehydes and NACs.

A novel uranyl organic framework (U-hdpcp) based on flexible cyclic triphosphazene polycarboxylate ligands was prepared, which possesses the ability to sense aromatic aldehyde solutions (benzaldehyde, salicylaldehyde and 2-bromobenzaldehyde) and nitro compounds (2,4,6-trinitrophenol, 2,4-dinitrophenol and o-nitrophenol). A fluorescent thin film based on U-hdpcp@PVA with the ability to sense aldehyde vapors was prepared via a spin coating method. The work expands the library of UOF materials based on large-sized carboxylic acid ligands and demonstrates promising applications in the field of fluorescent sensors.

Solvent-free room-temperature synthesis of brightly luminescent [BMPyr]2[SnCl4

The pseudo-ternary tin(II) halide [BMPyr]2[SnCl4] can be obtained just by mixing the starting materials [BMPyr]Cl and SnCl2 at room temperature without additional solvents. The compound shows bright Sn(II)-based emission of deep-red light (λmax: 740 nm) with a quantum yield of 88 ± 3% after optimised synthesis. Characterization is performed by X-ray structure analysis, infrared and fluorescence spectroscopy. Exemplary fluorescent thinfilms are realized by solvent processing.

An Efficient and Reversible Singlet Oxygen Quencher for Suppressing Photobleaching of Organic Fluorescent Dyes

AbstractQuenching singlet oxygen is the key to improve photostability of fluorescent dyes. We have systematically studied the capability of a new singlet oxygen quencher, DABCOnium (an alkylated derivative of 1,4‐diazabicyclo[2.2.2] octane) on removing singlet oxygen. Results showed that DABCOnium can significantly enhancing photostability of fluorescent thin films for more than 4.3 times compared with that without DABCOnium. After 2 hours of continuous irradiation, fluorescent film doped with DABCOnium retained 90 % of its original fluorescence intensity, which paves a new way in designing high performance singlet oxygen quenchers.

High-axial-resolution optical stimulation of neurons in vivo via two-photon optogenetics with speckle-free beaded-ring patterns

Two-photon optogenetics has become an indispensable technology in neuroscience, due to its capability in precise and specific manipulation of neural activities. A scanless holographic approach is generally adopted to meet the requirement of stimulating neural ensembles simultaneously. However, the commonly used disk patterns fail in achieving single-neuron resolution, especially in axial dimension, and their inherent speckles decrease stimulation efficiency. Here, we propose a novel speckle-free, beaded-ring pattern for high-axial-resolution optical stimulation of neurons in vivo. Using a dye pool and a fluorescent thin film as samples, we verify that, compared to those with disk patterns, higher axial resolution and better localization ability can be achieved with beaded-ring patterns. Furthermore, we perform two-photon based all-optical physiology with neurons in mouse S1 cortex in vivo, and demonstrate that the axial resolution obtained by beaded-ring patterns can be improved by 24% when stimulating multiple neurons, compared to that of disk patterns.

In-situ electro-polymerization of fluorescent electrochromic thin films based on charge-transfer complexes

Fluorescent electrochromic (FEC) materials, which reversibly change their both fluorescence and absorption via electrochemical reactions in response to applied potentials, have received extensive attention. Herein we directly obtained poly (2Z,2′Z)-3,3′-(1,4-phenylene)bis(2-(4-((6-(9H-carbazol-9-yl)hexyl)oxy)phenyl)acrylonitrile) P(CHDCS) and poly (2Z,2′Z)-3,3′-(2,5-dimethoxy-1,4-phenylene)bis(2-(4-((6-(9H-carbazol-9-yl)hexyl)oxy)phenyl)acrylonitrile) P(CHDCSM) as thin films on electrodes via electro-polymerization (EP) from linear donor-acceptor (D-A) monomers with isolated π-conjugation. Surprisingly, interchain charge-transfer complexes (CTCs) with mixed D-A stacks were generated between electroactive bis-carbazole (D) and luminescent dicyanodistyrylbenzene (A) units during the EP process. Consequently, significantly redshifted and bright orange fluorescence (∼600 nm) originated from intermolecular CT excitons were observed from both polymers, which could be reversibly switched upon applied potentials. This is the first time that the CTCs have been prepared via EP and applied as FEC materials. Moreover, the stronger intermolecular CT effect gives rise to an enhancement of electrical conductivity and FEC response in P(CHDCS), resulting in high optical contrasts (T = 33.6%, Ion/Ioff = 28.3) and fast FEC switching (coloring 1.25 s, fading 0.53 s, quenching 2.40 s, brightening 6.17 s) as well as good reversibility. In addition, the CTCs improve the spin delocalization of bis-carbazole radical cations, leading to increased color stability of the FEC films by a decay of only 1.2% in 2 h with no power supply after coloration. This work not only affords an innovative CTC design strategy for FEC materials but also paves the way for constructing highly-performed and energy-efficient FECs via one-step electrochemical methods.

A Quick Responsive Chitosan‐Oxine Based Thin Film to Recognize and Remove Zn2+ Ions from Potable Water

AbstractThrough the functionalization of chitosan (CS) with an oxine derivative, 8‐hydroxy‐2‐methyl‐quinoline5,7‐ sulfonyl chloride (HQSC), a thin film was prepared (CS‐HQSC). The film can recognize and adsorb Zn2+ ions from the aqueous samples. The sensor performances were characterized by UV‐Visible and fluorescence spectroscopic analysis. The weakly fluorescent thin film becomes highly fluorescent in the presence of Zn2+ ions. The solution‐phase study of the functionalized material shows a 30‐fold fluorescence enhancement in the presence of Zn2+ ions. The chelation of Zn2+ ions with CS‐HQSC could be the reason for the fluorescence enhancement. The chelation restricts the excited‐state proton transfer in the quinoline ring and facilitates chelation enhanced fluorescence. The sensor showed a linear detection of Zn2+ ions from 0.2 to 2 ppm, with the lowest detection limit of 0.08 ppm. The practical applicability studies of the sensor prove that the sensor film is quick responsive (30 seconds) and recyclable in acid solution. Also, the functionalized material CS‐HQSC shows 96 % removal of Zn2+ ions from the water samples.