Tunable Spectral Properties Research Articles

Tailoring of Spectral Behaviors in Ce3+-Activated Ba2Gd8(SiO4)6O2 Cyan-Emitting Phosphors via Site Substitution Engineering for Plant Growth and Full-Spectrum White Light-Emitting Diodes.

Highly efficient Ce3+-activated Ba2Gd8(SiO4)6O2 (BGSO) cyan-emitting phosphors were designed to simultaneously fulfill the applications of plant growth and a white-light-emitting diode (white-LED). Here, the spectral behaviors of the studied samples are manipulated by arranging Ce3+ to occupy various crystallographic sites (i.e., Ba2+ and Gd3+) in BGSO host lattices. Upon ultraviolet light excitation, all the samples emit an intense asymmetric broadband emission from Ce3+ and its fluorescence intensity is strongly impacted by the dopant concentration and occupied position. In addition, the resultant phosphors do not only possess satisfied thermal stability but also present high internal and extra quantum efficiencies of 78.6 and 61.8%, respectively, which can be regulated by selecting the substituted sites. Two cyan-emitting LEDs are fabricated by integrating the synthesized phosphors, and their emission bands align well with the absorption peaks of plant pigments, enabling their uses in plant growth. Furthermore, the controlled plant growth environments also clarify that the packaged cyan-emitting LED can effectively promote plant growth. Additionally, via adopting the resulting phosphors as cyan-emitting converters, full-spectrum white-LED with good electroluminescence behaviors is developed. These findings manifest that the Ce3+-activated BGSO phosphors with tunable spectral properties are promising cyan-emitting components for both artificial plant growth LED and full-spectrum white-LED.

Nitrated benzothiadiazole-based D-A electrochromic polymers with tunable spectral properties

Nitrated benzothiadiazole (BT) is the promising acceptor units in constructing D-A-D electrochromic polymers, but its researches in the electrochromic field was very limited so far. In this work, four kinds of nitrated polymer precursors (Th-NO2-BT, EDOT-NO2-BT, Th-2NO2-BT, and EDOT-2NO2-BT) were synthesized by Stille coupling reaction with EDOT and thiophene units as the end groups (electron donor units) and mono-nitrated benzothiadiazole and di-nitrated benzothiadiazole as the core groups (electron acceptor units). The chemical structure and optical properties of the precursor were investigated by means of 1H NMR, UV–vis absorption and fluorescence spectra; the corresponding mono-nitrated polymer films were obtained in CH2Cl2-Bu4NPF6 system by electrochemical deposition method. The optical band gap of di-nitrated polymer precursor is obviously larger than the corresponding mono-nitrated polymer precursor (both ultraviolet and fluorescence spectra are obviously blue-shifted), accompanied with the obvious increased initial oxidation potential. Due to the fluorescence quenching effect of -NO2 group, their absolute quantum yields are all very low (0.0006–0.015). The spectroelectrochemistry and electrochromic kinetics of mono-nitrated polymer films (P(Th-NO2-BT) and P(EDOT-NO2-BT)) were studied. It was found that P(EDOT-NO2-BT) can show better electrochromic performance than P(Th-NO2-BT), with dark green in the neutral state and more obvious electrochromic performance in the near-infrared region (optical contrast: 38.4 %, coloration efficiency: 129.1 cm2/C, and fast response time: 1.4 s). This systematically study about the effects of nitro substitution effect on the properties of D-A electrochromic polymers, which will further expand the selection of the new acceptor units and the application prospect of nitrated electrochromic materials.

Tunable spectral properties of PVB/WS2 impregnated fabrics in VIS, IR and RF part of the EMS

The application of nanomodified polymer impregnation on knitted polyester fabrics was studied to improve camouflage characteristics in VIS, IR, and RF domains to enhance multispectral camouflage protection. Nanoparticles of tungsten disulfide (WS2) were dispersed in an ethanol solution of poly (vinyl butyral) (PVB) and applied as a thin impregnation on polyester fabrics already dyed in camouflage shades. A reference sample impregnated only with PVB, without WS2, was also prepared in the same way. Parallel to the impregnated fabrics, a neat knitted polyester textile sample was submitted to all the examination methods. Diffuse reflection, specular gloss, and color coordinates were measured for all the samples. Moreover, the samples were observed using IR thermography in medium and long-wavelength infrared parts of the electromagnetic spectrum. The best suppression (≥20%) in the IR range of EMS was achieved for the dark green shade sample by applying PVB alone and/or adding PVB/ WS2. RF domain measurement analysis of how impregnated fabrics influence effective Radar Cross Section (RCS), K band radar was used, with the measurements done in terrain conditions. The decrease of the mean RCS value between 11% and 41% was achieved. The obtained results indicate that the addition of WS2 has a positive effect on the observed characteristics and that there is a possibility of using this newly impregnated knitwear in the wider area of the EMS as a camouflage material.

Enhanced Lifetime of Cyanine Salts in Dilute Matrix Luminescent Solar Concentrators via Counterion Tuning.

Organic luminophores offer great potential for energy harvesting and light emission due to tunable spectral properties, strong luminescence, high solubility, and excellent wavelength-selectivity. To realize their full potential, the lifetimes of luminophores must extend to many years under illumination. Many organic luminophores, however, have a tendency to degrade and undergo rapid photobleaching, leading to the perception of intrinsic instability of organic molecules. In this work we demonstrate that by exchanging the counterion of a heptamethine cyanine salt the photostability and corresponding lifetime of dilute cyanine salts can be enhanced by orders of magnitude from 10 hours to an extrapolated lifetime of greater than 65,000 hours under illumination. To help correlate and comprehend the underlying mechanism behind this phenomenon, the water contact angle and binding energy of each pairing were measured and calculated. We find that increased water contact angle, and therefore increasing hydrophobicity, generally correlate to improved lifetimes. Similarly, a lower absolute binding energy between cation and anion correlates to increased lifetimes. Utilizing the binding energy formalism, we predict the stability of a new anion and experimentally verify with good consistency. Moving forward, these factors could be used to rapidly screen and identify highly photostable organic luminophore salt systems for a range of energy harvesting and light emitting applications.

Stimulated Resonance Raman and Excited-State Dynamics in an Excitonically Coupled Bodipy Dimer: A Test for TD-DFT and the Polarizable Continuum Model.

Bodipy is one of the most versatile and studied functional dyes due to its myriad applications and tunable spectral properties. One of the strategies to adjust their properties is the formation of Bodipy dimers and oligomers whose properties differ significantly from the corresponding monomer. Recently, we have developed a novel strategy for synthesizing α,α-ethylene-bridged Bodipy dimers; however, their excited-state dynamics was heretofore unknown. This work presents the ultrafast excited-state dynamics of a novel α,α-ethylene-bridge Bodipy dimer and its monomeric parent. The dimer's steady-state absorption and fluorescence suggest a Coulombic interaction between the monomeric units' transition dipole moments (TDMs), forming what is often termed a "J-dimer". The excited-state properties of the dimer were studied using molecular excitonic theory and time-dependent density functional theory (TD-DFT). We chose the M06 exchange-correlation functional (XCF) based on its ability to reproduce the experimental oscillator strength and resonance Raman spectra. Ultrafast laser spectroscopy reveals symmetry-breaking charge separation (SB-CS) in the dimer in polar solvents and the subsequent population of the charge-separated ion-pair state. The charge separation rate falls into the normal regime, while the charge recombination is in the inverted regime. Conversely, in nonpolar solvents, the charge separation is thermodynamically not feasible. In contrast, the monomer's excited-state dynamics shows no dependence on the solvent polarity. Furthermore, we found no evidence of significant structural rearrangement upon photoexcitation, regardless of the deactivation pathway. After an extensive analysis of the electronic transitions, we concluded that the solvent fluctuations in the local environment around the dimer create an asymmetry that drives and stabilizes the charge separation. This work sheds light on the charge-transfer process in this new set of molecular systems and how excited-state dynamics can be modeled by combining the experiment and theory.

2,7-Diaminobenzopyrylium Dyes Are Live-Cell Mitochondrial Stains.

Small-molecule fluorescent stains enable the imaging of cellular structures without the need for genetic manipulation. Here, we introduce 2,7-diaminobenzopyrylium (DAB) dyes as live-cell mitochondrial stains excited with violet light. This amalgam of the coumarin and rhodamine fluorophore structures yields dyes with high photostability and tunable spectral properties.

Fluorescent amino acids as versatile building blocks for chemical biology.

Fluorophores have transformed the way we study biological systems, enabling non-invasive studies in cells and intact organisms, which increase our understanding of complex processes at the molecular level. Fluorescent amino acids have become an essential chemical tool because they can be used to construct fluorescent macromolecules, such as peptides and proteins, without disrupting their native biomolecular properties. Fluorescent and fluorogenic amino acids with unique photophysical properties have been designed for tracking protein-protein interactions in situ or imaging nanoscopic events in real time with high spatial resolution. In this Review, we discuss advances in the design and synthesis of fluorescent amino acids and how they have contributed to the field of chemical biology in the past 10 years. Important areas of research that we review include novel methodologies to synthesize building blocks with tunable spectral properties, their integration into peptide and protein scaffolds using site-specific genetic encoding and bioorthogonal approaches, and their application to design novel artificial proteins, as well as to investigate biological processes in cells by means of optical imaging.

Induction, control, and rationalization of supramolecular chirogenesis using metalloporphyrin tweezers: a structure-function correlation.

Supramolecular chirogenesis is one of the most rudimentary topics in the interdisciplinary sciences and essentially deals with various natural processes and innovative modern technologies. A comprehensive and rigorous understanding of such phenomenon is necessary to have a clear insight into the fundamental mechanisms and the various controlling factors, which would eventually lead to a range of practical applications of chiral supramolecular science. Metalloporphyrin tweezers have been extensively employed for such chirogenic processes due to their exciting physicochemical and tunable spectral properties, large stabilities, easily available synthetic protocols, and excellent abilities to form molecular assemblies. During the last few decades, various metalloporphyrin tweezers have been developed and considerably utilized by several research groups for assigning the absolute configuration to a variety of chiral diamines, conjugates of primary and secondary amines, amino alcohols, secondary alcohols, α-chiral carboxylic acids, etc. Our group has been at the forefront in trying to establish the structure-property correlation in this important area of interdisciplinary research. A brief account of our systematic investigation for understanding the underpinning mechanism of chirality induction and control at the molecular level over the last few years is presented in this Perspective article. The comprehensive understanding of such mechanistic details will be helpful in understanding various natural processes and designing modern technologies for various chirogenic functions in the fields of molecular sensors, nanotechnology, and supramolecular chemistry.

Benzoxazine monomers containing triphenylimidazole: Polymerization of monomers and properties of polybenzoxazines

In this study, two novel benzoxazine monomers containing triphenylimidazole (TBZ) and triphenylimidazolium (MTBZ) moieties are synthesized and fully characterized. The thermal ring-opening polymerization process of the two monomers is monitored by the 1H NMR and GPC analyses, which demonstrates that such a polymerization proceeds through a rearrangement of ketal-type linkage in the main chain into Mannich-type polymer along with the fast increasing in molecular weight. The structures of the triphenylimidazole-containing polybenzoxazines, poly-TBZ and poly-MTBZ, are verified by 1H NMR and FT-IR spectroscopies, and the thermal and mechanical properties of such polybenzoxazines are investigated by TGA and DMA analyses. Owing to the good solubility of poly-TBZ and poly-MTBZ in common organic solvents, poly-TBZ can be easily converted into poly-MTBZ through a facile post-modification approach. More importantly, the poly-TBZ shows the acid-dependent spectral properties due to formation of amine salts, whereas poly-MTBZ can be used as a chemodosimeter for the detection of Ag+, which exhibits high selectivity, good linearity and naked-eye distinguishable color change. This strategy can be utilized to prepare triphenylimidazole-containing polybenzoxazines with good solubility and tunable spectral properties, thereby extending their functionalities and applications.

π-Conjugated Donor-Acceptor Systems as Metal-Free Sensitizers for Dye-Sensitized Solar Cell Applications

High extinction coefficients and easily tunable spectral properties of π - conjugated donor-acceptor dyes are of superior advantage for the design of new metal- free organic sensitizers for applications in dye-sensitized solar cells. Ultrafast transient absorption spectroscopy on the femtosecond and nanosecond time scales provided deep insights into the dependence of charge carrier dynamics in fully organic dye/TiO2 systems on i) the donor-acceptor distance, ii) the π-conjugation length, and iii) the coupling to TiO2 by different anchoring groups. Importantly, the observed differences in charge transfer dynamics justify the variations of photovoltaic performances of the dyes as applied in solar cell devices. This leads to the conclusion that the photoconversion efficiencies strongly depend on a delicate interplay between the dyes’ building blocks, i.e. the donor, the π-conjugated spacer and the anchor/acceptor moieties, and may easily be tuned by molecular design.

Tunable size and spectral properties of fluorescent nanoGUMBOS in modified sodium deoxycholate hydrogels.

Microstructures of sodium deoxycholate hydrogels were altered considerably in the presence of variable tris(hydroxymethyl)aminomethane (TRIS) concentrations. These observations were confirmed by use of X-ray diffraction, polarized optical microscopy, rheology, and differential scanning calorimetry measurements. Our studies reveal enhanced gel crystallinity and rigidity with increasing TRIS concentrations. The tunable hydrogel microstructures obtained under various conditions have been successfully utilized as templates to synthesize cyanine-based fluorescent nanoGUMBOS (nanoparticles from a group of uniform materials based on organic salts). A systematic variation in size (70-200 nm), with relatively low polydispersity and tunable spectral properties of [HMT][AOT] nanoGUMBOS, was achieved by use of these modified hydrogels. The gel microstructures are observed to direct the size as well as molecular self-assembly of the nanomaterials, thereby tuning their spectral properties. These modified hydrogels were also found to possess other interesting properties such as variable morphologies ranging from fibrous to spherulitic, variable degrees of crystallinity, rigidity, optical activity, and release profiles which can be exploited for a multitude of applications. Hence, this study demonstrates a novel method for modification of sodium deoxycholate hydrogels, their applications as templates for nanomaterials synthesis, as well as their potential applications in biotechnology and drug delivery.

Quantum quench dynamics and population inversion in bilayer graphene

The gap in bilayer graphene (BLG) can directly be controlled by a perpendicular electric field. By tuning the field through zero at a finite rate in neutral BLG, excited states are produced. Due to screening, the resulting dynamics is determined by coupled non-linear Landau-Zener models. The generated defect density agrees with Kibble-Zurek theory in the presence of subleading logarithmic corrections. After the quench, population inversion occurs for wavevectors close to the Dirac point. This could, at least in principle provide a coherent source of infra-red radiation with tunable spectral properties (frequency and broadening). Cold atoms with quadratic band crossing exhibit the same dynamics.

Simple Conjugation and Purification of Quantum Dot−Antibody Complexes Using a Thermally Responsive Elastin-Protein L Scaffold As Immunofluorescent Agents

Fluorescent quantum dots (QDs), because of their tunable spectral properties, are ideal for simultaneous multiplexed detection in an antibody array format. Despite these advantages, their widespread usage is limited by the costly and tedious conjugation and separation protocol. Herein, we report a simple platform for the direct conjugation and separation of highly luminescent CdSe-ZnS QD-antibody complexes using a genetically engineered polyhistidine tagged elastin-protein L fusion (His-ELP-PL). The principle of immunoassay-ready conjugates was to take advantage of the direct conjugation of QDs via metal coordination with the His tag, the unique temperature-responsive property of ELP, and the high affinity of the antibody-binding protein L domain toward IgGs. Simple separation of the QD- His-ELP-PL-IgG complex was achieved by thermally triggered precipitation without any interference on the QD functionality. The utility of the biofunctionalized OD probes was demonstranted in an antibody array for the detection of carcinoembryonic antigen.

Directing energy flow through quantum dots: towards nanoscale sensing

Nanoscale sensors can be created when an expected energetic pathway is created and then that pathway is either initiated or disrupted by a specific binding event. Constructing the sensor on the nanoscale could lead to greater sensitivity and lower limits of detection. To this end, quantum dots (QDs) can be considered prime candidates for the active components. Relative to organic chromophores, QDs have tunable spectral properties, show less susceptibility to photobleaching, have similar brightness, and have been shown to display electro-optical properties. In this review, we discuss recent articles that incorporate QDs into directed energy flow systems, some with the goal of building new and more powerful sensors and others that could lead to more powerful sensors.