Weak Absorption Bands Research Articles

Unveiling Suppressed Concentration Quenching Enhanced Broadband Near-Infrared Emitters.

Transition metal ions are exceptional emitters of broadband near-infrared (near-IR) luminescence, enabling various applications in photonics and optics; however, their weak absorption and excitation bands often limit conversion performance. Among potential sensitizers, Cr3+ stands out, allowing the excitation of Ni2+ with broadband visible-near-IR light while preserving luminescence properties. Nevertheless, concentration-induced quenching in doped luminescent solids fundamentally undermines brightness due to a trade-off between internal quantum efficiency and excitation energy dynamics. In this study, we demonstrate unprecedented brightness in the broadband near-IR photoluminescence (PL) of the Cr3+-Ni2+ system, where single, heavily doped Cr3+ exhibits minimal PL, and tuning Ni2+ concentration offsets the competitive relationship between the light emitter and quencher. By coupling InGaN light-emitting diodes (LEDs) with an ultrabroadband near-IR PL phosphor, we achieve phosphor-converted LEDs with a record output power of 41.5 mW at 100 mA and a photoelectric efficiency of 19.53% at 20 mA, nearly doubling previous reports. Our findings unveil intrinsic suppression of concentration quenching and eliminate competing energy sinks by emphasizing the dominant role of emitters in downshifting excitation energies, thus opening new avenues for the design of bright, sensitized luminescent materials.

9,10-Bis(5H-dibenzo[b,f]azepino)anthracene

The title compound with a donor–π–donor (D–π–D) type triad structure was synthesized by Buchwald–Hartwig amination using 9,10-dibromoanthracene and 5H-dibenzo[b,f]azepine, and characterized by 1H, 13C{1H} NMR, HRMS, and X-ray diffraction analysis. The azepine–anthracene–azepine units are nearly orthogonal to each other, with a torsion angle of 88°. A broad and weak absorption band around 410–480 nm and the low emission character (ΦF = 0.01) suggest the weak intramolecular charge transfer from the azepine to the anthracene unit due to the twisted structure.

Spectroscopic Properties of TmF3-Doped CaF2 Crystals.

In this study, we report the growth and comprehensive spectroscopic analysis of TmF3-doped CaF2 crystals, grown using the vertical Bridgman method. The optical absorption and photoluminescence properties of both trivalent (Tm3+) and divalent (Tm2+) thulium ions were investigated. Optical absorption spectra in the UV-VIS-NIR range reveal characteristic transitions of Tm3+ ions, as well as weaker absorption bands corresponding to Tm2+ ions. The Judd-Ofelt (JO) formalism was applied to determine the intensity parameters Ω2, Ω4, and Ω6, which were used to calculate radiative transition probabilities, branching ratios, and radiative lifetimes for the Tm3+ ions. The emission spectra showed concentration-dependent quenching effects, with significant emissions observed for the concentration of 0.1 mol% TmF3 under excitation at 260 nm and 353 nm for Tm3+ ions and at 305 nm for Tm2+ ions. A new UV emission associated with divalent Thulium is reported. The results indicate that higher TmF3 concentrations lead to increased non-radiative energy transfer, which reduces luminescence efficiency. These findings contribute to the understanding of the optical behavior of Tm-doped fluoride crystals, with implications for their application in laser technologies and radiation dosimetry.

Nondestructive and quick differentiation between loupe-clean low-alkali natural and hydrothermal synthetic aquamarines: Constraints of infrared spectroscopy

A considerable increase in the price of natural aquamarine has led to the emergence of hydrothermal synthetic aquamarine as a cheap substitute in the market. In this study, comparative analysis was conducted between natural aquamarine obtained from Altay Prefecture in Xinjiang, China, and hydrothermal synthetic aquamarine in the Chinese market to distinguish them with loupe-clean clarity. Nondestructive tests including microscopic observation, X-ray fluorescence spectroscopy, infrared spectroscopy, ultraviolet–visible–near-infrared spectroscopy, and Raman spectroscopy were conducted. The two samples were low-alkali aquamarine, dominated by type Ⅰ H2O, and the infrared spectra showed similar water-related peaks, exhibiting weak absorption bands related to Cl− at 2736 and 2449 cm−1 and CO2 in the crystal channels at 2358 cm−1. Apart from the strong irregular and distinctive growth patterns, infrared absorption bands at 3313 and 4060 cm−1 due to the N–H bond (derived from ammonium halide used in crystal growth) vibrations were found to be present only in hydrothermal synthetic aquamarine. This study reveals implications for identifying hydrothermal synthetic aquamarine when the internal features of loupe-clean aquamarine are not obvious.

Improved Methods for Retrieval of Chlorophyll Fluorescence from Satellite Observation in the Far-Red Band Using Singular Value Decomposition Algorithm

Solar-induced chlorophyll fluorescence (SIF) is highly correlated with photosynthesis and can be used for estimating gross primary productivity (GPP) and monitoring vegetation stress. The far-red band of the solar Fraunhofer lines (FLs) is close to the strongest SIF emission peak and is unaffected by chlorophyll absorption, making it suitable for SIF intensity retrieval. In this study, we propose a retrieval window for far-red SIF, significantly enhancing the sensitivity of data-driven methods to SIF signals near 757 nm. This window introduces a weak O2 absorption band based on the FLs window, allowing for better separation of SIF signals from satellite spectra by altering the shape of specific singular vectors. Additionally, a frequency shift correction algorithm based on standard non-shifted reference spectra is proposed to discuss and eliminate the influence of the Doppler effect. SIF intensity retrieval was achieved using data from the GOSAT satellite, and the retrieved SIF was validated using GPP, enhanced vegetation index (EVI) from the MODIS platform, and published GOSAT SIF products. The validation results indicate that the SIF products provided in this study exhibit higher fitting goodness with GPP and EVI at high spatiotemporal resolutions, with improvements ranging from 55% to 129%. At low spatiotemporal resolutions, the SIF product provided in this study shows higher consistency with EVI and GPP spatially.

The Population of Small Near-Earth Objects: Composition, Source Regions, and Rotational Properties

The study of small (<300 m) near-Earth objects (NEOs) is important because they are more closely related than larger objects to the precursors of meteorites that fall on Earth. Collisions of these bodies with Earth are also more frequent. Although such collisions cannot produce massive extinction events, they can still produce significant local damage. Here we present the results of a photometric and spectroscopic survey of small NEOs that include near-infrared spectra of 84 objects with a mean diameter of 126 m and photometric data of 59 objects with a mean diameter of 87 m. We found that S-complex asteroids are the most abundant among the NEOs, comprising ∼66% of the sample. Most asteroids in the S-complex were found to have compositions consistent with LL-chondrites. Our study revealed the existence of NEOs with spectral characteristics similar to those in the S-complex but that could be hidden within the C- or X-complex due to their weak absorption bands. We suggest that the presence of metal or shock darkening could be responsible for the attenuation of the absorption bands. These objects have been grouped into a new subclass within the S-complex called Sx-types. The dynamical modeling showed that 83% of the NEOs escaped from the ν 6 resonance, 16% from the 3:1, and just 1% from the 5:2 resonance. Lightcurves and rotational periods were derived from the photometric data. No clear trend between the axis ratio and the absolute magnitude or rotational period of the NEOs was found.

Hydrothermal synthesis of (C5H14N2)[CoCl4]⸳0.5H2O: Crystal structure, spectroscopic characterization, thermal behavior, magnetic properties and biological evaluation

The organic-inorganic compound (C5H14N2)[CoCl4]⸳0.5H2O, I, was characterized by various physicochemical techniques. The X-ray diffraction analysis revealed that the compound crystallizes in the centrosymmetric space group C2/c of the monoclinic system. The atomic arrangement the Co(II) complex is built from isolated [CoCl4]2– anions, 1-methylpiperazine-1,4-diium [C5H14N2]2+ cations and free water molecules. The crystal structure study showed that the cohesion of I is assured through N–H···Cl and N–H···O hydrogen bonds giving birth to a 3-D architecture. Hirshfeld surface analysis revealed that Cl···H/H···Cl and H···H (58.5 and 36.4%, respectively) are the most significant interactions between species. Minor O···H/H···O interactions are also present. The compound was characterized by thermal analysis, TGA-DTA showed the removal of the co-crystallized water before 100 °C and a first mass loss at around 120 °C. Magnetic measurements are in good agreement with isolated, S = 3/2, tetrahedral [CoCl4]2− anions. The negative Weiss constant of -1.35 indicates single-ion anisotropy and very weak antiferromagnetic interactions. UV–visible spectroscopy reveals three weak absorption bands in the visible range due to the d-d electronic transitions typical of the Co(II) tetra-coordinated. A bioassay showed antibacterial activity against the gram negative Klebsiella pneumonia and gram positive Bacillus ceureus, Listeria monocytogenes, and Micrococcus lutues.

The Spectral Characteristics of Lunar Agglutinates: Visible–Near‐Infrared Spectroscopy of Apollo Soil Separates

AbstractThe lunar surface evolves over time due to space weathering, and the visible–near‐infrared spectra of more mature (i.e., heavily weathered) soils are lower in reflectance and steeper in spectral slope (i.e., darker and redder) than their immature counterparts. These spectral changes have traditionally been attributed to the space‐weathered rims of soil grains (and particularly nanophase iron therein). However, understudied thus far is the spectral role of agglutinates—the agglomerates of mineral and lithic fragments, nanophase iron, and glass that are formed by micrometeoroid impacts and are ubiquitous in mature lunar soils. We separated agglutinates and non‐agglutinates from six lunar soils of varying maturity and composition, primarily from the 125–250 μm size fraction, and measured their visible–near‐infrared reflectance spectra. For each soil, the agglutinate spectra are darker, redder, and have weaker absorption bands than the corresponding non‐agglutinate and unsorted soil spectra. Moreover, greater soil maturity corresponds to darker agglutinate spectra with weaker absorption bands. These findings suggest that agglutinates (rather than solely the space‐weathered rims) play an important role in both the darkening and reddening of mature soils—at least for the size fractions examined here. Comparisons with analog soils suggest that high nanophase iron abundance in agglutinates is likely responsible for their low reflectance and spectrally red slope. Additional studies of agglutinates are needed both to more comprehensively characterize their spectral properties (across size fractions and in mixing with non‐agglutinates) and to assess the relative roles of agglutinates and rims in weathering‐associated spectral changes.

Оптические свойства триэтиламиниевой соли трифторуксусной кислоты

. Triethylaminium trifluoroacetate (CH3CH2)3NH+ ‒O(O)C‒CF3, obtained by reacting tri-fluoroacetic acid with triethylamine, is a colorless ionic liquid that passes into the vapor phase when heated to 200–220 °C. The compound has been characterized by elemental analysis, infrared spectroscopy, 1H and 13C nuclear magnetic resonance, mass spectroscopy, thermogravimetry, differential scanning calorimetry, refractometry, electron absorption and emission spectroscopy. In the UV spectrum there is a weak absorption band in the range of 260–340 nm. When excited at 320 nm, the compound shows two photoluminescence bands at 375 and 425 nm. The ionic liquid readily dissolves lanthanide coordination compounds: erbium(III) phenanthroline thenoyltrifluoromethyl acetonate Er(tta)3·phen, europium(III) tris(3-trifluoroacetamidobenzoyltrifluoroacetonate) and holmium(III) acetylacetonate Ho(acac)3. The absorption spectra of erbium(III), europium(III), holmium(III) β-diketonates and emission spectra of erbium(III) and europium(III) β-diketonates are presented.

Effect of doping on the optical properties of lanthanum-gallium tantalate

Nominally pure lanthanum-gallium tantalate La3Ga5.5Ta0.5O14 crystals doped with aluminum, silicon and gallium oxide to above stoichiometric content have been grown by the Czochralski technique in iridium crucibles in argon and in agron with addition of oxygen atmospheres. The transmittance spectra of the crystals have been measured on a Cary-5000 UV-Vis-NIR spectrophotometer in the 200–800 nm range. Absorption spectra α(λ) have been plotted on the basis of the experimental data. The absorption spectra of the undoped crystals grown in an oxygen-free atmosphere have one weak absorption band at λ ~ 290 nm. The absorption spectra of the crystals grown in an agron with addition of oxygen have absorption bands at λ ~ 290, 360 and 480 nm. We show that for the crystals grown in an oxygen-free atmosphere, gallium doping to above stoichiometric content reduces the intensity of its only λ ~ 290 nm absorption band. Aluminum doping of the La3Ga5.5Ta0.5O14 crystals grown in an oxygen-free atmosphere significantly reduces the intensity of the λ ~ 290 nm absorption band and increases the intensity of the λ ~ 360 and 480 nm bands. Aluminum doping of the La3Ga5.5Ta0.5O14 crystals grown in an oxygen-containing atmosphere reduces the intensity of the λ ~ 360 and 480 nm bands and increases the intensity of the λ ~ 290 nm absorption band. Silicon doping of these crystals significantly reduces the intensity of the λ ~ 480 nm band and also reduces the intensity of the λ ~ 290 and 360 nm bands.

INFLUENCE OF B2O3 ON THE INTERACTION IN THE SiO–GeO2 SYSTEM

The influence of the B2O3 additive on the nature of the interaction in the SiO–GeO2 system was investigated by X-ray diffraction and IR transmission spectroscopy. The nature of the diffractograms of the SiO–GeO2–B2O3 system with a composition of 1:1:0.5 and 1:1:1 corresponds to the presence of SiO2 phases of hexagonal modification (quartz) and GeO2 of various modifications, as well as, possibly, a crystalline B2O3 phase. The exact value of the content of the reaction products and initial components could not be determined due to the significant content of the X-ray amorphous component of unknown composition. The broadening of the diffraction peaks and the presence of a distinct halo testify to the benefit of the processes of nanostructuring and glass formation. However, the absence of elemental germanium in the SiO–GeO2–B2O3 system, in contrast to the SiO–GeO2 system, was clearly established. The nature of the IR transmission spectra of samples with different content of B2O3 additive differ significantly from each other. Thus, the IR transmission spectra of the sample with a composition of 1:1:0.5 contain weak absorption bands due to the oscillations of the B–O bonds; instead, they reveal periodic oscillations characteristic of nanostructured systems. In the spectra of the sample with a composition of 1:1:1, the absorption bands due to the oscillations of the B–O bonds are very distinct, but there are no oscillations. Therefore, the addition of B2O3 probably accelerates the formation of Germanium monoxide, which in turn reacts with the B2O3 additive and possibly with SiO2 as one of the reaction products. Testing of samples of the SiO–GeO2–B2O3 system by the method of thermal evaporation in a vacuum revealed the advantages of the sample with a composition of 1:1:1 in the ability to form a strong and durable coating. It was possible to determine the refractive index for it, which is 1.93 at a wavelength of 1000 nm. Instead, the coating obtained from the 1:1:0.5 composition sample turned out to be unstable. A conclusion was made about the need for further optimization of the composition and synthesis conditions to obtain materials with the required parameters.

Effect of doping on the optical properties of lanthanum-gallium tantalate

Nominally pure lanthanum-gallium tantalate La3Ga5.5Ta0.5O14 crystals doped with aluminum, silicon and gallium oxide to above stoichiometric content have been grown by the Czochralski technique in iridium crucibles in argon and in agron with addition of oxygen atmospheres. The transmittance spectra of the crystals have been measured on a Cary-5000 UV-Vis-NIR spectrophotometer in the 200–800 nm range. Absorption spectra α(λ) have been plotted on the basis of the experimental data. The absorption spectra of the undoped crystals grown in an oxygen-free atmosphere have one weak absorption band at λ ~ 290 nm. The absorption spectra of the crystals grown in an agron with addition of oxygen have absorption bands at λ ~ 290, 360 and 480 nm. We show that for the crystals grown in an oxygen-free atmosphere, gallium doping to above stoichiometric content reduces the intensity of its only λ ~ 290 nm absorption band. Aluminum doping of the La3Ga5.5Ta0.5O14 crystals grown in an oxygen-free atmosphere significantly reduces the intensity of the λ ~ 290 nm absorption band and increases the intensity of the λ ~ 360 and 480 nm bands. Aluminum doping of the La3Ga5.5Ta0.5O14 crystals grown in an oxygen-containing atmosphere reduces the intensity of the λ ~ 360 and 480 nm bands and increases the intensity of the λ ~ 290 nm absorption band. Silicon doping of these crystals significantly reduces the intensity of the λ ~ 480 nm band and also reduces the intensity of the λ ~ 290 and 360 nm bands.

An algorithm for correction of atmospheric scattering dilution effects in volcanic gas emission measurements using skylight differential optical absorption spectroscopy

Differential Optical Absorption Spectroscopy (DOAS) is commonly used to measure gas emissions from volcanoes. DOAS instruments measure the absorption of solar ultraviolet (UV) radiation scattered in the atmosphere by sulfur dioxide (SO2) and other trace gases contained in volcanic plumes. The standard spectral retrieval methods assume that all measured light comes from behind the plume and has passed through the plume along a straight line. However, a fraction of the light that reaches the instrument may have been scattered beneath the plume and thus has passed around it. Since this component does not contain the absorption signatures of gases in the plume, it effectively “dilutes” the measurements and causes underestimation of the gas abundance in the plume. This dilution effect is small for clean-air conditions and short distances between instrument and plume. However, plume measurements made at long distance and/or in conditions with significant atmospheric aerosol, haze, or clouds may be severely affected. Thus, light dilution is regarded as a major error source in DOAS measurements of volcanic degassing. Several attempts have been made to model the phenomena and the physical mechanisms are today relatively well understood. However, these models require knowledge of the local atmospheric aerosol composition and distribution, parameters that are almost always unknown. Thus, a practical algorithm to quantitatively correct for the dilution effect is still lacking. Here, we propose such an algorithm focused specifically on SO2 measurements. The method relies on the fact that light absorption becomes non-linear for high SO2 loads, and that strong and weak SO2 absorption bands are unequally affected by the diluting signal. These differences can be used to identify when dilution is occurring. Moreover, if we assume that the spectral radiance of the diluting light is identical to the spectrum of light measured away from the plume, a measured clean air spectrum can be used to represent the dilution component. A correction can then be implemented by iteratively subtracting fractions of this clean air spectrum from the measured spectrum until the respective absorption signals on strong and weak SO2 absorption bands are consistent with a single overhead SO2 abundance. In this manner, we can quantify the magnitude of light dilution in each individual measurement spectrum as well as obtaining a dilution-corrected value for the SO2 column density along the line of sight of the instrument. This paper first presents the theory behind the method, then discusses validation experiments using a radiative transfer model, as well as applications to field data obtained under different measurement conditions at three different locations; Fagradalsfjall located on the Reykjanaes peninsula in south Island, Manam located off the northeast coast of mainland Papua New Guinea and Holuhraun located in the inland of north east Island.

Bodipy−corrole tetrads as heavy−atom−free triplet photosensitizers: Study of the energy transfer and application in triplet−triplet annihilation upconversion

Free base corrole can generate triplet state without invoking of heavy−atom effect, however, its weak and narrow absorption band in the visible spectral range make corrole not an ideal triplet photosensitizer. Herein, novel Bodipy−corrole tetrads were prepared by attaching visible light-harvesting antennae of Bodipy or electron spin converter with fullerene units (2B−Tur−Cor and B−C60−Tur−Cor) to solve the above problems, which show a stronger and broader absorption band in the visible region, and the maximum molar absorption coefficient is up to 2.58 × 105 M−1 cm−1 at 504 nm for 2B−Tur−Cor. By using of fluorescence spectroscopy, steady-state and time-resolved transient absorption spectroscopic methods, the singlet energy transfer progress from the Bodipy moiety to the corrole moiety was confirmed. Through fluorescence lifetimes and fluorescence excitation spectrum study, the rate constant of the singlet energy transfer was calculated as 9.58 × 107 s−1 for 2B−Tur−Cor and 2.45 × 108 s−1 for B−C60−Tur−Cor, respectively. The TD−DFT computation suggests that the first and second triplet state is localized in the corrole moiety and the Bodipy moiety for 2B−Tur−Cor, respectively, and the triplet state energy was calculated to be 1.37 eV and 1.61 eV, respectively. Nanosecond time−resolved transient difference absorption spectra show that the triplet excited states of these tetrads are localized on corrole unit, the lifetime of 2B−T−Cor is up to 143 μs, however, the lifetime of B−C60−Tur−Cor is only 3.3 μs. Long-lived triplet excited states play important role in applications of the triplet photosensitizers in photocatalysis or other photophysical processes concerning triplet–triplet−energy−transfer. As a proof of concept, these tetrads were used as heavy−atom−free organic triplet photosensitizers for triplet−triplet annihilation based upconversion. The upconversion quantum yield was up to 5.86% for 2B−Tur−Cor, however, it is only 0.52% for B−C60−Tur−Cor.

SYNTHESIS AND PHOTOCHEMICAL PROPERTIES OF NOVEL AZOQUINOLINE CONTAINING POLYMERS

The development of modern technologies are constantly requires seeking new low-cost, efficient materials and establish new technical methods for application these materials. Synthesis of polymers with predicted and expected properties on the one hand and using specific features of interaction light with photoactive fragments in polymers, on the other hand, opens new prospects of application for new materials based on these polymers. The side chain methacrylic polymers with different active functional group have been well studied and widely applied in many fields, such as optoelectronics, nonlinear optics, optical storage materials, biochemicals, and medicine.&#x0D; The present work focused on synthesis new azostyrylcontaining methacrylic monomers and copolymers with methylmetacrylate (MMA) based on these monomers. The pre­sent study is a first reported notice of the synthesis and photochemical properties of methacrylic polymers with 6-azo-phenylquinoline frag­ments in side chain. Moreover in this work the features of syntheses have been described in detail for monomers and polymers based on new azocompounds. Absorption spectroscopic properties for new quinoline polymers with azo fragment were investigated with UV-Vi­sible spectrophotometry in THF solutions. All studi­ed polymers show a strong absorption band in the range of 300–375 nm resulting from π-π* electronic transition and a weak absorption band in the range of 400–490 nm assigned to n-π* transitions. Electron donating and electron withdrawing substituents at quinoline moity of azo-quinoline polymer solutions lead to bathochromic shift of the π-π*absorption band which agrees well with the result of work. We found that this red-shift increases with an increase of electron donating strength of the substituent as well as with an increase of electron withdrawing strength of the substituent. Based on of the result achieved we can suppose that irradiation of polymers with azo fragment lead to photoinduced trans-cis-isomerization.&#x0D; From the obtained and presented results one can conclude that novel quinoline polymers with azo fragment can be considered as promising materials for applications requiring photosensitivity in certain of range of wavelength.

Efficient Zn2+ doping into CsBr nanocrystals using benzoyl bromide

The potential route to induce effective metal doping into the colloidal nanocrystal (NC) lattice is still limited due to the unfavorable energy cost and needs further investigation for colloidal chemistry involved in the optical properties and device development with optimized NC design. In this study, we reports a bright blue emitting Zn2+-doped CsBr NCs (6.7 at.%) by introducing reactive benzoyl bromide to promote a preferential reaction with metal cations that are not favorably incorporated into the CsBr lattice. In particular, the acyl group (R-C = O-) of benzoyl bromide is more effective to adopt additional metal cations into the crystal lattice during the nucleation and growth process of colloidal CsBr NCs compared to alkylammonium bromides with long hydrocarbon chains, providing a new synthetic route for metal doping into the metal halide perovskites NCs. Zn2+-doped CsBr NCs exhibit a blue PL emission at 425 nm with a Stokes shift of 113 nm for the weak absorption band edge.

Green preparation of electrically conductive solution blow spun nanofibers from recycled polyethylene terephthalate via plasma-assisted oxidation-reduction.

Simple and green strategy was described for the development of multifunctional polyester nanofibers (PNFs). Solution blow spinning (SBS) technology was applied to in situ immobilize nanocomposites of polyaniline (PANi) and silver nanoparticles (AgNPs) into plasma-treated polyester nanoscaled fibers prepared. The polyester nanofibers were prepared from recycled polyethylene terephthalate waste, which was exposed plasma-curing and a REDOX reaction in the presence of AgNO3, aniline, and CH3COONH4. Plasma-catalyzed oxidative polymerization of aniline to polyaniline together with a reductive process of Ag+ to silver nanoparticles led to their enduring insoluble dispersion into the surface of polyester nanofibers. By taking the advantage of the PANi oxidation, AgNPs were precipitated from an aqueous medium of AgNPs. The morphological properties were investigated by various analytical techniques. The polyester fiber diameter was determined in the range of 450-650nm. In addition, transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were utilized to examine AgNPs, demonstrating diameters of 4-20nm. The plasma-uncured AgNPs/PANi immobilized nanofibrous film displayed weak absorption bands at 399nm and 403nm upon increasing the concentration of AgNPs. On the other hand, the plasma-cured AgNPs/PANi immobilized nanofibers displayed strong absorption bands at 526nm and 568nm upon increasing the concentration of AgNPs. The AgNP-induced antimicrobial performance and the PANi-induced electrically conductivity were explored. The prepared PNFs showed high UV protection.

A Switchable Near‐Infrared‐Absorbing Dye Based on Redox‐Bistable Benzitetraazaporphyrin

AbstractActivatable near‐infrared (NIR) dyes responsive to external stimuli are used in medical and other applications. Here, we describe the design and synthesis of bench‐stable 18π‐ and 20π‐electron benzitetraazaporphyrins (BzTAPs) possessing redox‐switchable NIR properties. X‐Ray, NMR, and UV/Visible‐NIR analyses revealed that 20π‐electron BzTAP 1 exhibits NIR absorption and antiaromaticity with a paratropic ring‐current, while 18π‐electron BzTAP 2 shows weakly aromatic character with NIR inertness. Notably, the NIR‐silent BzTAP 2 was readily converted to the NIR‐active BzTAP 1 in the presence of mild reducing agents such as amine. The intense NIR absorption band of BzTAP 1 is in sharp contrast to the very weak absorption bands of previously reported antiaromatic porphyrinoids. Molecular orbital analysis revealed that symmetry‐lowering perturbation of the 20π‐electron porphyrinoid skeleton enables the HOMO–LUMO transition of 1 to be electric‐dipole‐allowed. BzTAPs are expected to be useful for constructing activatable NIR probes working in reductive environments.

A Switchable Near-Infrared-Absorbing Dye Based on Redox-Bistable Benzitetraazaporphyrin.

Activatable near-infrared (NIR) dyes responsive to external stimuli are used in medical and other applications. Here, we describe the design and synthesis of bench-stable 18π- and 20π-electron benzitetraazaporphyrins (BzTAPs) possessing redox-switchable NIR properties. X-Ray, NMR, and UV/Visible-NIR analyses revealed that 20π-electron BzTAP 1 exhibits NIR absorption and antiaromaticity with a paratropic ring-current, while 18π-electron BzTAP 2 shows weakly aromatic character with NIR inertness. Notably, the NIR-silent BzTAP 2 was readily converted to the NIR-active BzTAP 1 in the presence of mild reducing agents such as amine. The intense NIR absorption band of BzTAP 1 is in sharp contrast to the very weak absorption bands of previously reported antiaromatic porphyrinoids. Molecular orbital analysis revealed that symmetry-lowering perturbation of the 20π-electron porphyrinoid skeleton enables the HOMO-LUMO transition of 1 to be electric-dipole-allowed. BzTAPs are expected to be useful for constructing activatable NIR probes working in reductive environments.

Crystal-Chemical and Spectroscopic Study of Gem Sphalerite from Banská Štiavnica, Slovakia

A complex crystal-chemical investigation based on spectroscopic methods, Electron MicroProbe Analysis (EMPA), and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) was made on sphalerite samples from the Terézia and Rozália veins in the Banská Štiavnica ore district. The yellow (sample A) and olive-green sphalerite (C) are in association only with quartz; orange sphalerite (B) is associated with quartz and chalcopyrite; and black sphalerite (D) is associated with galena, chalcopyrite, quartz, and baryte. EMPA revealed that Cd and Fe are substituting for Zn with variable proportions; the Cd/Fe ratio decreases from 2.82–2.85 in the A sample to 0.42 in the D sample. LA-ICP-MS showed that, except Cd and Fe, only Mn has content above 20; Co and Cu vary between 2 and 17 ppm. The optical absorption spectra exhibit absorption between 644 and 740 nm with three smaller humps at 669–671, 698–702, and 732–743 nm, and weaker absorption bands at 858–894 nm in the NIR region, which can be all assigned to crystal-field transitions of Fe2+. The absorption edge starts at about 600 nm to the UV region. Minimal absorption is in the yellow-red part of the visible spectrum giving rise to yellowish-orange and orange-red colors. Absorption in the red region for olive-green sphalerite is more pronounced, explaining the shift to greenish hues. In black sphalerite, the absorption pattern is similar to the olive-green sphalerite, but the bands in the 644 to 740 nm region are less defined. The black color could be caused by slightly higher concentrations of Fe, the smaller size of individual crystals in the aggregate reducing macroscopic transparency, and/or the presence of submicroscopic inclusions.