Luminescent Dye Research Articles

Novel Approach for Detecting Vapors of Acids and Bases with Proton-Transfer Luminescent Dyes Encapsulated within Metal–Organic Frameworks

Luminescent metal-organic frameworks (LMOFs) are one of the most promising materials for being implemented as active layers in the fabrication of photonic devices such as luminescent sensors of harmful chemicals. It is highly desirable that these materials undergo quantifiable spectroscopic (absorption or emission) changes in the presence of vapors of those analytes, as in many industrial processes, these toxic compounds are in the gas phase. Although great progresses have been achieved in the field, in most of the examples reported hitherto, the detection of chemicals by LMOFs is attained in solution. Herein, we present a novel approach consisting of the encapsulation of proton transfer dyes (8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt, HPTS, and 3-hydroxyflavone, 3-HF) within the pores of two distinct MOFs. The trapped proton transfer dyes (PT-dyes) may exist as different structures (enol, anion, or zwitterion), each of these exhibiting unique optical properties. Indeed, our findings reveal that the dyes can be encapsulated as anionic or enol species. Remarkably, the PT-dye@MOF composites exhibit a high luminescence quantum yield (up to 30%), which is sensitive (showing shifting in the emission wavelengths with a concomitant quenching/enhancement of the intensity) in the presence of vapors of an acid (HCl) and a base (triethylamine). These results open a novel avenue for the development of smarter vapoluminescent MOF-based materials.

Programming and Dynamic Control of the Circular Polarization of Luminescence from an Achiral Fluorescent Dye in a Liquid Crystal Host by Molecular Motors

AbstractCircular polarized light is utilized in communication and display technologies and a major challenge is to develop systems that can be switched between left and right circular polarized luminescence with high degrees of polarization and enable multiple addressable stable states. Luminescent dyes in Liquid Crystal (LC) cholesteric phases are attractive systems to generate, amplify and modulate circularly polarized luminescence (CPL). In the present study, we employ light‐driven molecular motors as photo‐controlled chiral dopants in LCs to switch the handedness of the LC and the circular polarization of luminescence from an achiral dye embedded in the mesogenic material. Tuning of the color of the CPL and the retention time of the photoprogrammed helicity is demonstrated making use of a variety of motors and dyes. The flexibility offered by the design based on inherently chiral unidirectional rotary motors provides full control over CPL non‐invasively by light, opening possibilities for pixilated displays with externally addressable polarization.

Programming and Dynamic Control of the Circular Polarization of Luminescence from an Achiral Fluorescent Dye in a Liquid Crystal Host by Molecular Motors.

Circular polarized light is utilized in communication and display technologies and a major challenge is to develop systems that can be switched between left and right circular polarized luminescence with high degrees of polarization and enable multiple addressable stable states. Luminescent dyes in Liquid Crystal (LC) cholesteric phases are attractive systems to generate, amplify and modulate circularly polarized luminescence (CPL). In the present study, we employ light-driven molecular motors as photo-controlled chiral dopants in LCs to switch the handedness of the LC and the circular polarization of luminescence from an achiral dye embedded in the mesogenic material. Tuning of the color of the CPL and the retention time of the photoprogrammed helicity is demonstrated making use of a variety of motors and dyes. The flexibility offered by the design based on inherently chiral unidirectional rotary motors provides full control over CPL non-invasively by light, opening possibilities for pixilated displays with externally addressable polarization.

Sensors in a Flash! Oxygen Nanosensors for Microbial Metabolic Monitoring Synthesized by Flash Nanoprecipitation.

Flash nanoprecipitation (FNP) is an efficient and scalable nanoparticle synthesis method that has not previously been applied to nanosensor fabrication. Current nanosensor fabrication methods have traditionally exhibited poor replicability and consistency resulting in high batch-to-batch variability, highlighting the need for a more tunable and efficient method such as FNP. We used FNP to fabricate nanosensors to sense oxygen based on an oxygen-sensitive dye and a reference dye, as a tool for measuring microbial metabolism. We used fluorescence spectroscopy to optimize nanosensor formulations, calibrate the nanosensors for oxygen concentration determination, and measure oxygen concentrations through oxygen-sensitive dye luminescence. FNP provides an effective platform for making sensors capable of responding to oxygen concentration in gas-bubbled solutions as well as in microbial environments. The environments we tested the sensors in arePseudomonas aeruginosa biofilms andSaccharomyces cerevisiae liquid cultures—both settings where oxygen concentration is highly dependent on microbial activity. With FNP now applied to nanosensor fabrication, future nanosensor applications can take advantage of improved product quality through better replicability and consistency while maintaining the original function of the nanosensor.

Effects of Nanoscale Morphology on Optical Properties of Photoluminescent Polymer Optical Fibers.

Bicomponent photoluminescent polymer optical fibers (PL-POFs) have been melt-spun and in-situ drawn to different extents. The results suggest that scattering in the sheath can effectively increase the photoluminescent dye excitation probability in the fiber core. The core/sheath PL-POFs are made of a semi-crystalline fluoropolymer sheath of low refractive index (RI) and an amorphous cycloolefin polymeric core of high RI, which is doped with a luminescent dye. The axial light emission, as well as the guiding attenuation coefficients of the core/sheath PL-POFs, have been measured using a side-illumination set-up. The incident blue laser is down-converted to red light, which is re-emitted and partially guided by the core. The axial light emission is measured at the fiber tip as a function of the distance from the illumination position to the integrating sphere. It is demonstrated that the presence of a semi-crystalline sheath significantly enhances the axial light emission and that it also lowers the attenuation coefficient, compared to the emission and guiding properties of PL core-only fibers. Additionally, the attenuation coefficient has been found to be lower in more strongly drawn PL-POFs. Wide-angle X-ray diffraction and small-angle X-ray scattering experiments reveal structural differences in differently drawn PL-POFs that can be linked to the observed differences in the optical properties.

Tunable emission color of [(2-mb)tpp]2Cd1-xMnxCl4 (x = 0–1) solid solutions synthesized via mechanochemical method for anti-counterfeit luminescent paper and WLEDs

Zero-dimensional (0D) hybrid metal halides (HMHs) have received widespread concern due to their unique structures and splendid luminescent properties. However, the syntheses of HMHs primarily rely on crystal growth methods in solution or ion-thermal conditions, which are time-consuming and require extensive use of organic solvents. On the other hand, the reported HMHs usually exhibiting only one emission color hinder their further applications. Herein, we report a series of 0D HMHs solid solutions of [(2-mb)tpp]2Cd1-xMnxCl4 [(2-mb)tpp = (2-methylbenzyl)triphenylphosphine and x = 0–1] synthesized through a facile mechanochemical method. The emission color of [(2-mb)tpp]2Cd1-xMnxCl4 can be tuned from purplish-blue, bluish-green, to green light by adjusting the Cd/Mn molar ratio or excitation wavelength. Thus different luminescent panda and quick response (QR) code patterns can be designed with [(2-mb)tpp]2Cd1-xMnxCl4 as luminescent dyes for potential applications in multicolor imaging and anti-counterfeiting encryption. Moreover, owing to the excellent thermal stability, the as-fabricated white light emitting diode (WLED) with [(2-mb)tpp]2MnCl4 as the green phosphor possesses an applicable correlated color temperature (CCT = 5305 K), an ultrahigh color rendering index (CRI, Ra = 95.4), and the CIE chromaticity coordinates of (0.3386, 0.3864) corresponding to pure white light. This work provides guidance for the rapid, facile, economical, and large-scale synthesis of HMHs with multiple luminescent centers, and exhibits the development of these materials in potential applications such as anti-counterfeiting luminescent papers and WLEDs.

Dye-modified halide perovskite materials

Halide perovskites have been successfully adopted as the cutting-edge solar cell materials owing to their excellent optoelectronic properties; yet, further performance enhancement is required to realize their wide industrial deployment. In this manuscript, we review recent progresses of the “dye-modified halide perovskite materials” for perovskite solar cells, where the concept of the dye-modified perovskite materials is proposed to exploit the intricate dye···perovskite interactions and combines the merits of the molecular dyes and the halide perovskite materials toward the enhanced optoelectronic performance and stability of perovskite solar cells. The detailed interactions between the dyes and the halide perovskite materials are explained. The organic and organometallic dyes that have been successfully deployed for the perovskite solar cells are discussed, which includes the porphyrin dyes, ruthenium dyes, luminescent dyes and a series of D-π-A organic dyes. The structural design parameters of the dyes that are compatible with the halide perovskite materials are elucidated, such as the anchoring groups, π-conjugation, aggregation and charge redistribution motifs. Finally, suggestions on the future development of the dye-modified halide perovskite materials for solar cells are provided. This manuscript facilitates the fundamental understanding of the dye···perovskite interactions and anticipates further deployment of the dye-modified perovskite materials for optoelectronic and energy applications. • Diverse categories of dyes improve perovskite solar cell performance. • Correlations between dyes and perovskites' optoelectronic properties are revealed. • Anchors, π-groups and side groups of the dyes dictate perovskite properties. • Suggestions for future efforts on dye-sensitized perovskites materials are provided.

Towards facile fabrication of photonics components from inorganic and hybrid sol-gel films. Preparation and optical properties characterization

New trends towards development of integrated optics and miniaturization of photonic devices require fabrication of miniaturized photonic components. Fabrication of waveguiding films with designed optical properties is a fundamental process for production of planar integrated devices.We report here preparation of thin layers based on TiO2 precursor (TET – titanium(IV) ethoxide) and SiO2 precursors, namely inorganic (TEOS – tetraethyl orthosilicate) or organically modified (GLYMO − 3-glycidoxypropyltrimethoxysilane) as candidates for potential application in the planar integrated circuits.The thin layers were deposited on soda-lime glass substrates using the sol-gel method and dip-coating technique and processed at relatively low temperature (up to 300 °C). Several parameters e.g. a) the type of SiO2 precursor, b) the presence of complexing agent for TET and c) heat treatment temperature were tested for their influence on thickness and refractive index of the obtained films.Furthermore, a few series of sol-gel films activated with luminescent dye (Rhodamine B) was fabricated. The influence of the above-listed parameters on luminescent properties of the films was characterized because of lack of systematic study in the literature in this aspect. Moreover, a spectrum of the light at the output of a chosen luminescent dye-doped waveguiding film excited by laser source was investigated.In addition, the subject of our investigations were films prepared at 200 °C with various amounts of TET and organically modified SiO2 precursor in concentration range not presented before. Their optical properties such as homogeneity and values of optical band gap of TiO2 clusters were explored. For selected samples the waveguide properties including the optical losses were evaluated. For the first time, hybrid films with presented composition and refractive index in range of 1.59–1.71 were used for patterning by nanoimprint technique allowing for reproduction of periodic structures, which may serve for example as grating couplers or DFB (distributed feedback) resonators.

Probing the Local Polarity in Biocompatible Nanocarriers with Solvatofluorochromism of a 4-Carbazole-1,8-naphthalimide Dye

The study of local polarity at the nanoscale is of crucial importance for the development of smart drug delivery systems and photonic materials and is frequently accomplished with the use of luminescent tracer dyes. Nile Red is often used for this purpose, owing to its polarity-sensitive internal charge transfer transition, but its performance is affected by specific solute-solvent interactions that prevent its widespread applicability. Herein, we develop a new 1,8-naphthalimide dye with a strong charge-transfer transition that results in a large dipole moment change upon excitation. This leads to luminescence properties with high sensitivity to solvent polarity, that are independent of specific or inductive interactions. These properties are explored to probe the polarity of biocompatible nanocarriers. This dye was effective in probing the properties of polymeric nanoparticles, allowing the accurate calculation of polarity descriptors and dielectric constants.

Excitation wavelength-dependent continuous color-tunable luminescence of fluorescent dyes encapsulated into lanthanide metal-organic framework for anti-counterfeiting

Excitation dependent luminescent materials, which have attracted significant scientific attention in the field of information security owing to information storage and luminescence properties. However, it remains a formidable challenge in developing excitation dependent luminescent materials with a simple synthesis method and predictably modulated luminescent outputs. Herein, a novel Ln3+/Fluorescent dyes@MOFs strategy is developed to generate excitation dependent continuous color-changing luminescent materials via a hydrothermal method and post-synthetic modification (PSM), based on metal-organic frameworks (MOFs) matrix doped with lanthanide cations and fluorescent dyes encapsulated into the lanthanide MOFs. The continuous proportional emission of mixed luminescence appeared within a single matrix in response to the different excitation wavelength and the proportional emission control (PEC) mechanism between the two luminescent centers is proposed. In addition, the photoluminescence platform demonstrates a distinct security method based on covert color that are controlled by distinct excitation wavelengths and excellent luminescence stability have also been verified in these new materials.

Real‐Time Tunable Red/Near‐Infrared Solid‐State Emitters in the First Biological Window: 9,9‐Diethyl‐2‐diphenylaminofluorene‐Based Push‐Pull Fluorophores for Distributed Feedback and Random Lasing Applications

AbstractIn biological imaging, red‐to‐infrared emissive dyes facilitate direct visualization of molecular interactions, through deep tissue penetration, along with minimal tissue damage. This work uses simple systems based on a single dye‐doped polymeric thin film for distributed feedback and random lasing investigations. As active compounds, novel push‐pull luminescent diphenylaminofluorene derivatives are used, functionalized with different acceptor groups. Integration of such luminescent dyes with a transparent polymeric medium allows fabrication of real‐time lasing tunability in the first biological window (650–950 nm). The observed spectral tuning of 150 nm is a groundbreaking value obtained in a single‐dye system.

Controlled Synthesis of Luminescent Xanthene Dyes and Use of Ionic Liquid in Thermochromic Reaction.

In this study, we demonstrate six novel xanthene derivatives and their spectroscopic and chemical properties. The presented synthesis examination allowed us to obtain two different compounds during one step, with open and closed lactone rings substituted with different length alkyl chains. Increasing the reaction efficiency to 77% was obtained using the microwave-assisted method. Moreover, the modification of O-alkylation synthesis in an ecofriendly way using a ball mill led to achieving exclusively one opened ring product. All of the synthesized compounds showed different spectroscopic behaviors in comparison with the different organic dyes; the typical concentration quenching of luminescence was not observed. The relationship between the length of the alkyl chain and the time of luminescence decay is presented. Synthetized closed forms of dyes turned out to be promising leuco dyes. For the first time, an ionic liquid was used as a developer of synthesized xanthene derivatives (as leuco dyes), which led to obtaining an irreversible thermochromic marker.

Chemical Doping of a Silica Matrix with a New Organic Dye from the Group of Heterocyclic Compounds—Chemical, Optical and Surface Characteristics

This paper presents the results of research on a luminescent dye bound in a silica matrix. The new developed dye from the group of azaheterocyclic compounds was used: 3-(p-hydroxyphenyl)-1-phenyl-1H-pyrazolo [3,4-b]quinoxaline. The structure and composition of the dye was examined by 1HNMR, 13CNMR, FTIR, and elemental analysis. Its absorption and photoluminescence characteristics were tested in solvents of different polarity in UV-Vis range. The films were prepared by sol–gel method and dip-coating technique. The dye was introduced into a sol in the course of a synthesis of the latter. DLS and FTIR measurements of sols were performed. Optical properties were investigated using UV-Vis spectrophotometry and monochromatic ellipsometry. The surface morphology of the layers was examined by atomic force microscopy. Our investigations showed that the dye bound in the silica matrix does not lose its photoluminescent properties. The emission band at λPL = 550 nm (λex = 365 nm) was recorded for the dye in the matrix. The layers are optically homogeneous with smooth surfaces. Dye doped silica films have RMS surface roughness of 2.17 nm over areas of 2 × 2 μm2. The idea of binding a photoluminescent dye in a silica matrix presented in the paper can be applied in the technology of luminescent solar concentrators.

Luminescence of Reichardt's dye in polyelectrolyte-modified saponite colloids

Reichardt’s dye (RD) exhibits solvatochromic properties across the entire visible spectrum. This work reports, for the first time, luminescence of RD in colloidal systems of layered silicate saponite (Sap) modified with poly(diallyldimethylammonium) polycations (PDDA), and provides an interpretation of this unique phenomenon. The application of tailored theoretical chemistry methods such as DFT and other approaches supplies a theoretical interpretation of the phenomenon to supplement the results of the experiments. RD luminescence was achieved by preventing the movement of molecules and suppressing non-radiative relaxation processes. This effect only occurred if the negatively-charged phenolate group in the RD molecule interacted with the positively-charged groups of the PDDA cations, while at the same time the positively-charged pyridinium group was also adsorbed onto the negatively-charged Sap siloxane surface. Only at small coverage of the Sap surface by PDDA cations is there sufficient fixation of the RD molecules for them to exhibit luminescent properties. The results suggest that the application of this dye may be extended to luminescent probes, which could be used to characterize the distribution of charge centers on the surfaces of various materials, biopolymers, biological tissues, etc.

Sunlike White Light-Emitting Diodes Based on Rare-Earth-Free Luminescent Materials.

Solid-state lighting (SSL) sources based on light-emitting diodes represent the new generation of highly efficient illumination systems that significantly impact energy-saving. The development of white light-emitting diodes (WLEDs) with a combination of high color rendering index (CRI) and high deep-red color rendering R9 is an important challenge in the field of solid-state lighting. On the other hand, most WLEDs use rare-earth inorganic luminescent materials. The annual demand for rare-earth metals has doubled to 125,000 tons in 15 years, and the demand is projected to reach 315,000 tons in 2030. The explosion in demand for these materials, combined with a monopolistic supply source, represents a real risk for the development of WLEDs in the next few years. Luminescent organic materials are a relevant and promising alternative. Here, we report a WLED with a very high CRI of 95.7 and R9 of 78.7, obtained using a combination of a blue LED chip (excitation source) and two organic luminescent dyes (Coumarin 6 and Lumogen Red) acting as spectral converters in a multilayer remote phosphor configuration. To the best of our knowledge, this is the first rare-earth-free WLED with such high values of CRI and R9.

Advances in quantum dots as diagnostic tools.

Quantum dots (QDs) are crystalline inorganic semiconductor nanoparticles a few nanometers in size that possess unique optical electronic properties vs those of larger materials. For example, QDs usually exhibit a strong and long-lived photoluminescence emission, a feature dependent on size, shape and composition. These special optoelectronic properties make them a promising alternative to conventional luminescent dyes as optical labels in biomedical applications including biomarker quantification, biomolecule targeting and molecular imaging. A key parameter for use of QDs is to functionalize their surface with suitable (bio)molecules to provide stability in aqueous solutions and efficient and selective tagging biomolecules of interest. Researchers have successfully developed biocompatible QDs and have linked them to various biomolecule recognition elements, i.e., antibodies, proteins, DNA, etc. In this chapter, QD synthesis and characterization strategies are reviewed as well as the development of nanoplatforms for luminescent biosensing and imaging-guided targeting. Relevant biomedical applications are highlighted with a particular focus on recent progress in ultrasensitive detection of clinical biomarkers. Finally, key future research goals to functionalize QDs as diagnostic tools are explored.

Universal Figure of Merit of Luminescent Dye Solar Concentrators

Universal Figure of Merit of Luminescent Dye Solar Concentrators

White-light emission from organic aggregates: a review

White light, which contains polychromic visible components, affects the rhythm of organisms and has the potential for advanced applications of lighting, display, and communication. Compared with traditional incandescent bulbs and inorganic diodes, pure organic materials are superior in terms of better compatibility, flexibility, structural diversity, and environmental friendliness. In the past few years, polychromic emission has been obtained based on organic aggregates, which provides a platform to achieve white-light emission. Several white-light emitters are sporadically reported, but the underlying mechanistic picture is still not fully established. Based on these considerations, we will focus on the single-component and multicomponent strategies to achieve efficient white-light emission from pure organic aggregates. Thereinto, single-component strategy is introduced from four parts: dual fluorescence, fluorescence and phosphorescence, dual phosphorescence with anti-Kasha’s behavior, and clusteroluminescence. Meanwhile, doping, supramolecular assembly, and cocrystallization are summarized as strategies for multicomponent systems. Beyond the construction strategies of white-light emitters, their advanced representative applications, such as organic light-emitting diodes, white luminescent dyes, circularly polarized luminescence, and encryption, are also prospected. It is expected that this review will draw a comprehensive picture of white-light emission from organic aggregates as well as their emerging applications.

Development of Efficient One-Pot Methods for the Synthesis of Luminescent Dyes and Sol-Gel Hybrid Materials.

This paper presents a comparison of the simultaneous preparation of di-O-alkylated and ether–ester derivatives of fluorescein using different methods (conventional or microwave heating). Shortening of the reaction time and increased efficiency were observed when using a microwave reactor. Moreover, described here for the first time is the application of a fast, simple, and eco-friendly ball-assisted method to exclusively obtain ether–ester derivatives. We also demonstrate that fluorescein can be effectively functionalized by O-alkylation carried out under microwave or ball-milling conditions, saving time and energy and affording the desired products with good yields and minimal byproduct formation. All the synthesized products as well as pH-dependent (prototropic) forms trapped in the SiO2 matrix were examined using UV–Vis and fluorescence spectroscopy.

Encapsulation of aggregation-caused quenching dye in metal-organic framework as emissive layer of organic light-emitting diodes

Direct use of commercial luminescent dyes as an emissive layer for organic light-emitting diodes (OLEDs) has limitations due to aggregation-caused quenching (ACQ) effect of the dyes in solid state. Highly porous metal-organic frameworks (MOFs) have been employed as a host to prevent aggregation of dye molecules. A prototype Al-based MOF (MIL-100) was synthesized as a processable fluid gel and fabricated as thin film with sub-100 nm thickness for further encapsulation of ACQ dye. Luminescence of Coumarin 6 dye in MOF film was preserved in solid state with a quantum yield of 21.4%. The obtained composite film was directly used as an emissive layer for OLED fabrication. The device was turned on at low voltage of 4.4 V with the maximum electroluminescence and external quantum efficiency of 1.65 × 103 cd m−2 and 0.9%, respectively. This study shows the potential of using commercial ACQ dyes that are incorporated in porous platform as Emissive layer for OLED applications.