Wavelength Dependence Research Articles

Phototransposition of Indazoles to Benzimidazoles: Tautomer‐Dependent Reactivity, Wavelength Dependence, and Continuous Flow Studies

Herein, we report a detailed investigation of the photomediated transformation of indazoles to benzimidazoles through a nitrogen‐carbon transposition. This phototransposition is known to occur in low yield when 1H‐indazoles are subjected to high‐energy UVC irradiation. The 2H‐tautomer of indazole absorbs light more strongly than the 1H‐tautomer at longer wavelengths. We leveraged this improved absorbance profile to develop a general system for the high‐yielding conversion of N2‐derivatized indazoles (prepared from the corresponding 1H‐indazoles) to the corresponding benzimidazoles under UVB or UVA irradiation in up to 98% yield. Investigation of the substrate scope revealed a strong correlation between reaction yield and electron density at N2 of the indazole substrate, suggesting the importance of the availability of the lone pair at this position for reaction efficiency. In addition, evaluation of wavelength‐dependent reactivity through the generation of a photochemical action plot revealed that the highest conversion does not only occur at the substrate's maximum absorbance wavelength but also on its red‐side, enabling the use of longer wavelength irradiation to achieve high yields. Building on these insights, a continuous flow protocol was established that enables the phototransposition on preparative scale.

Phototransposition of Indazoles to Benzimidazoles: Tautomer-Dependent Reactivity, Wavelength Dependence, and Continuous Flow Studies.

Herein, we report a detailed investigation of the photomediated transformation of indazoles to benzimidazoles through a nitrogen-carbon transposition. This phototransposition is known to occur in low yield when 1H-indazoles are subjected to high-energy UVC irradiation. The 2H-tautomer of indazole absorbs light more strongly than the 1H-tautomer at longer wavelengths. We leveraged this improved absorbance profile to develop a general system for the high-yielding conversion of N2-derivatized indazoles (prepared from the corresponding 1H-indazoles) to the corresponding benzimidazoles under UVB or UVA irradiation in up to 98% yield. Investigation of the substrate scope revealed a strong correlation between reaction yield and electron density at N2 of the indazole substrate, suggesting the importance of the availability of the lone pair at this position for reaction efficiency. In addition, evaluation of wavelength-dependent reactivity through the generation of a photochemical action plot revealed that the highest conversion does not only occur at the substrate's maximum absorbance wavelength but also on its red-side, enabling the use of longer wavelength irradiation to achieve high yields. Building on these insights, a continuous flow protocol was established that enables the phototransposition on preparative scale.

Wavelength dependence of photoresponse in tin(IV) oxide nanowire-based ultraviolet photodetectors

Wavelength dependence of photoresponse in tin(IV) oxide nanowire-based ultraviolet photodetectors

Large Faraday Rotation in Pyrolysis Synthesized Carbon Dots

Pyrolysis of citric acid produced carbon dots on the 10 nm size scale, tunable by synthesis time. Magneto-optical spectroscopy revealed a size-dependent Faraday rotation. For particles with optimal synthesis time, the Verdet constant was measured as >300 times larger than that of water on a per-mass basis. Introducing ethylenediamine substrate as a nitrogen dopant in the synthesis resulted in a similar effect. These behaviors are indicative of extended sp2 networks in the particles. A strong wavelength dependence with largest rotation at the shortest measured wavelength of 405 nm was observed. This dependence is explained by a comparison with the theory of electron-photon interactions, which predicts an increase of the Verdet constant with 1/(ω02-ω2)2 for an angular frequency ω and an absorption line at ω0. The fitting of the analytical function to the measured Faraday rotation indicates a wavelength near 300 nm corresponding to the ω0, consistent with an extended electron delocalization. Nanomaterials with large magneto-optical effects have new proposed technological applications, such as in their use as magnetic field sensors. The Faraday rotation is related to spin-induced effects, foremost nuclear spin optical rotation, suggesting further applications of these materials for the optical readout of spin states in quantum information science.

Probing the rest-frame wavelength dependence of quasar variability. Insights from the Zwicky Transient Facility Survey

Quasar variability can potentially unlock crucial insights into the accretion process. Understanding how this variability is influenced by wavelength is crucial for validating and refining quasar variability models. This paper aims to enhance the understanding of the dependence of variability on the rest-frame wavelength (λ_RF) by isolating the variance in different timescales in well-defined wavelength bins and examining the corona-heated accretion disk (CHAR) model. We investigated the relation between variance and rest-frame wavelength (λ_RF) using optical g- and r-band light curves from the Zwicky Transient Facility (ZTF) Data Release 15 (DR15) for ∼ 5000 quasars within narrow ranges of the black hole mass (M_BH) and Eddington ratio (R_Edd). A spectral model taking into account disk continuum emission, Balmer transitions, Fe II pseudo-continuum emission, and other emission lines is necessary to best interpret the variance spectrum. Our analysis indicates a strong anticorrelation between median variance and λ_RF for quasars with M_ BH M_ ⊙ and R_ Edd at different timescales. This anticorrelation is more pronounced at shorter timescales. The results align well with a bending power-law power spectral density (PSD) model with both the damping timescale and the high-frequency slope of the PSD depending on the wavelength. The predictions provided by the CHAR model on the variance spectrum across most timescales studied showcase its potential in constraining temperature variations within the accretion disk.

Phase-resolved Hubble Space Telescope WFC3 Spectroscopy of the Weakly Irradiated Brown Dwarf GD 1400 and Energy Redistribution–Irradiation Trends in Six White Dwarf–Brown Dwarf Binaries

Abstract Irradiated brown dwarfs offer a unique opportunity to bridge the gap between stellar and planetary atmospheres. We present high-quality Hubble Space Telescope/Wide Field Camera 3/G141 phase-resolved spectra of the white dwarf–brown dwarf binary GD 1400, covering more than one full rotation of the brown dwarf. Accounting for brightness variations caused by ZZ Ceti pulsations, we revealed weak (∼1%) phase-curve amplitude modulations originating from the brown dwarf. Subband light-curve exploration in various bands showed no significant wavelength dependence on amplitude or phase shift. Extracted day- and nightside spectra indicated chemically similar hemispheres, with slightly higher dayside temperatures, suggesting efficient heat redistribution or the dominance of radiative escape over atmospheric circulation. A simple radiative and energy redistribution model reproduced the observed temperatures well. Cloud-inclusive models fit the day and night spectra better than cloudless models, indicating global cloud coverage. We also begin qualitatively exploring atmospheric trends across six irradiated brown dwarfs, from the now complete “Dancing with the Dwarfs” white dwarf–brown dwarf sample. The trend we find in the dayside/nightside temperature and irradiation levels is consistent with efficient heat redistribution for irradiation levels less than ∼109 erg s−1 cm−2 and decreasing efficiency above that level.

Excited-State Proton Transfer Dynamics of Cyanonaphthol in Protic Ionic Liquids: Concerted Effects of Basicity of Anions and Alkyl Carbons in Cations.

Excited-state proton transfer (ESPT) reactions of 5-cyano-2-naphthol (5CN2) and 5,8-dicyano-2-naphthol (DCN2) were investigated in protic ionic liquids (PILs) composed of quaternary ammonium (NnnnH+) (n = 2, 4, or 8) and hexanoate (C5H11COO-) using time-resolved fluorescence spectroscopy. The effects of the number of alkyl carbons in the cation and the basicity of the anion on the reaction yield and dynamics were examined. In a series of [NnnnH][C5H11COO], fluorescence from the hydrogen-bonding complex (AHBX-*) of a proton-dissociated form (RO-*) with a solvent acid in the electronic excited state was observed between the fluorescence bands of an acidic form (ROH*) and an anionic form (RO-*) as in the case of [N222H][CF3COO] (Fujii et al., J. Phys. Chem B, 2017, 121, 6042). The yield, formation rate, and decay rate of AHBX-* were assessed by the steady-state fluorescence intensity ratio of AHBX-* to RO-* and by analysis of the time-resolved fluorescence spectra within several tens of nanoseconds. The stability of AHBX-* was significantly different from that in [N222H][CF3COO] and depended on the number of alkyl carbons in the cation. The formation of AHBX-* was quite fast compared to the case in [N222H][CF3COO] and almost close to the excitation pulse width. Excitation wavelength dependence of the fluorescence dynamics was observed within several hundred picoseconds for the series of [NnnnH][C5H11COO]. The origin was ascribed to the complex with solvent IL formed in the electronic ground state, as suggested by the density-functional theory (DFT) calculations.

Cobalt Hydroxide Modification of TiO2 Nanosheets for Visible-Light-Responsive Photocatalysts.

To make full use of sunlight for water splitting reactions for hydrogen production, a visible-light-driven photocatalyst was developed by modifying TiO2 nanosheets with Co(OH)2. By adding an aqueous Co(NO3)2·6H2O solution to a TiO2 nanosheet suspension, the TiO2 nanosheets aggregated and Co(OH)2 was formed. In the ultraviolet-visible (UV-vis) diffuse reflectance spectrum of the photocatalyst, new absorption bands attributable to Co(OH)2 and the interfacial charge transfer between Co(OH)2 and the TiO2 nanosheets appeared at around 600 and 400 nm, respectively. The photocatalytic activity of Co(OH)2/TiO2 nanosheets was evaluated in terms of the O2 evolution reaction in an aqueous AgNO3 solution, finding that the reaction proceeds under visible light. Furthermore, the investigation of the wavelength dependence of the photocatalytic activity revealed that the photocatalytic reaction on Co(OH)2/TiO2 nanosheets proceeds via Co(OH)2 photocatalysis and interfacial charge transfer between Co(OH)2 and the TiO2 nanosheets under visible light irradiation.

The Optical Extinction Law Depends on Magnetic Field Orientation: The RV–ψ Relation

Abstract For aspherical interstellar dust grains aligned with their short axes preferentially parallel to the local magnetic field, the amount of extinction per grain is larger when the magnetic field is along the line of sight and smaller when in the plane of the sky. To the extent that optical extinction arises from both aligned and unaligned grain populations with different extinction properties, changes in the magnetic field orientation induce changes in its wavelength dependence, parameterized by R V ≡ A V /E(B − V). We demonstrate that the measured total and polarized extinction curves of the diffuse Galactic interstellar medium imply R V varies from 3.21 when the magnetic field is along the line of sight (ψ = 0) to R V = 3.05 when in the plane of the sky (ψ = 90°). This effect could therefore account for much of the large-scale R V variation observed across the sky (σ(R V ) ≃ 0.2), particularly at high Galactic latitudes.

Coexistence Demonstration and Wavelength Dependency Analysis of S-Band CV-QKD Signal with Fully Loaded C+L-Band DWDM Signals.

We demonstrated the coexistence of an S-band CV-QKD signal with fully loaded C+L-band classical signals for the first time. The secret key rate of the S-band QKD system was 986 kbps with the C+L-band WDM signals transmitted through a 20 km G.654.E fiber link. We also revealed that the S-band CV-QKD performance limiting factor under the C+L-band WDM condition is the spontaneous Raman scattering light similar to the C-band CV-QKD performance limiting factor, confirming the validity of estimating the wavelength dependency of the secret key rate under the WDM condition from the fiber loss and the spontaneous Raman scattering light power. These results show that the CV-QKD performance under the C+L band WDM conditions becomes comparable to that under the C-band WDM conditions by wavelength design in the S-band.

ТЕМПЕРАТУРАНЫҢ ҚИҒАШ БРЭГГ ТОРЛАРЫНЫҢ ПАРАМЕТРЛЕРІНЕ ӘСЕРІ

The presented article states that various control methods based on optical technologies are currently relevant and are used in areas other than engineering and science. It is said that there is interest in Bragg gratings, including oblique Bragg gratings. The history of the oblique Bragg grating is briefly discussed, and its definition is given. Focusing on their features, the main formulas were reviewed in detail. Brief details of the conducted research are given, and data on experiments performed in certain temperature ranges are given. Sets of spectral characteristics are given, and graphs of temperature dependence of Bragg and host wavelengths of OBG are given. At the same time, the temperature sensitivity and coefficients of OBG were calculated and the results were presented in the form of a table.

Reactive Radical Etching of Quartz by Microwave Activated CH4/H2 Plasmas Promotes Gas Phase Nanoparticle Formation.

An attenuation of visible probe radiation identified in earlier absorption studies of microwave plasma-activated CH4/H2/Ar gas mixtures is shown to arise from nanoparticles in under-pumped regions on opposing sides of a reactor used for diamond chemical vapor deposition. The present modeling studies highlight (i) ejection of Si-containing species into the gas phase by reactive radical etching of the quartz window through which the microwave radiation enters the reactor, enabled by suitably high window temperatures (TSiO2) and the synergistic action of near-window H atoms and CyHx radicals; (ii) subsequent processing of the ejected material, some of which are transported to and accumulate in stagnation regions in the entrance to the reactor side arms; and (iii) the importance of Si in facilitating homogeneous gas phase nucleation, clustering, and nanoparticle growth in these regions. The observed attenuation, its probe wavelength dependence, and its variations with changes in process conditions can all be rationalized by a combination of absorption and scattering contributions from Si/C/H containing nanoparticles with diameters d in the range of 50-100 nm. Possible implications for Si incorporation in CVD diamond samples are discussed.

Photoconduction in 2D Single‐Crystal Hybrid Perovskites

AbstractSingle‐crystal hybrid perovskites represent an emerging class of next‐generation semiconductors due to their excellent and tunable optoelectronic properties, along with a solution‐based, low‐temperature growth process. 2D single‐crystal hybrid perovskites are especially promising as their long‐range ordered multiple quantum well structure induces many peculiar properties, such as large exciton binding energy, large in‐plane conductivity, and improved environmental stability, which make them suitable for low‐dimensional optoelectronics applications and fundamental studies. Herein, the structural properties, morphology, and optoelectronic behavior of 2D thin film phenethylammonium lead iodide (PEA2PbI4) single‐crystals, synthesized using the space‐confined growth technique are explored. A planar device is fabricated and its spectral photoresponse is studied under broadband supercontinuum white light. Remarkably, the device exhibits an ultra‐low dark current (10−14 A), indicative of low defect density and suppressed ion migration. Under white light, the current increases linearly with the incident power, up to a factor of 105, and the device achieves a specific detectivity of 109 Jones. The temperature and wavelength dependence of the photocurrent suggests the dissociation of excitons as one of the main mechanisms affecting photoconduction. Furthermore, stability under air exposure and illumination turns out to be remarkable.

Ultrafast Intelligent Sensor for Integrated Biological Fluorescence Imaging and Recognition.

Fluorescence imaging and recognition are core technologies in targeted medicine, pathological surgery, and biomedicine. However, current imaging and recognition systems are separate, requiring repeated data transfers for imaging and recognition that lead to delays and inefficiency, hindering the capture of rapidly changing physiological processes and biological phenomena. To address these problems, we propose an integrated intelligent sensor for biological fluorescence imaging and ultrafast recognition. This sensor integrates an imaging system based on a photodetector array and a recognition system based on neural networks on a single chip, featuring a highly compact structure, a continuously adjustable optical response, and reconfigurable electrical performance. The unified architecture of the imaging and recognition systems enables ultrafast recognition (19.63 μs) of tumor margins. Additionally, the special organic materials and bulk heterojunction structure endow the photodetector array with strong wavelength dependence, achieving high specific detectivity (3.06 × 1012 Jones) in the narrowband near-infrared range commonly used in biomedical imaging (600-800 nm). After training, the sensor can accurately recognize biological fluorescence edges in real time, even under interference from other colored light noise. Benefiting from its rapidity and high accuracy, we demonstrated a simulated surgical experiment showcasing tumor edge fluorescence imaging, recognition, and cutting. This integrated approach holds the potential to establish a novel paradigm for designing and manufacturing intelligent medical sensors.

Self-similar solutions of the bed deformation

In this paper, a conclusion about the self-similar behavior of the bed surface evolution is made. It is based on the analysis of experimental and numerical studies of the bed surface evolution under the mechanical impact of liquid flow. The bottom wave has a form close to one period of a sinusoidal function with a time-varying wavelength and constant steepness. A method of constructing the automodel dependence of the bed surface on time and spatial coordinate in analytical form is proposed. It was shown that it is enough to select five bottom surfaces with given wavelengths from a series of shapes. Next, the mean values of shear stresses are calculated for them, and the rates of change of wavelengths are found. Then a degree of approximation of the wavelength dependence of its rate of change is determined, and, finally, the exact solution of the corresponding differential equation is obtained. Comparison with experimental data and numerical solutions shows that the solution error does not exceed a few percent and that computational time is reduced by 25–30 times.

Wavelength-Dependent DNA Damage Induced by Single Wavelengths of UVC Light (215 to 255 nm) in a Human Cornea Model.

Scientific bodies overseeing UV radiation protection recommend safety limits for exposure to ultraviolet light in the workplace based on published peer-reviewed data. To support this goal, a 3D model of the human cornea was used to assess the wavelength dependence of corneal damage induced by UVC light. In the first set of experiments the models were exposed with or without simulated tears; at each wavelength (215-255 nm) cells with DNA dimers and their distribution within the epithelium were measured. Simulated tears reduced the fraction of damaged cells to an extent dependent on the wavelength and tissue layer. Another set of models were exposed without tears; yields of DNA-damaged cells and their distribution within the corneal epithelium were evaluated at each wavelength, together with other markers of cell and tissue integrity. Unlike relatively longer wavelengths, the range commonly referred to as far-UVC (215-235 nm) only induced dimers in the uppermost layers of the epithelium and did not result in lasting damage or halt proliferation of the germinative cells. These results provide evidence for the recommended exposure limits for far-UVC wavelengths, which have been proposed as a practical technology to reduce the risk of transmission of airborne diseases in occupied locations.

Probing electronic-structure pH-dependency of Au nanoparticles through X-ray Absorption Spectroscopy

Research on gold nanoparticles (Au NPs) remains a field of intense activity due to their broad range of applications in diverse fields like catalysis, renewable energy, environmental science, and medicine. Herein, the morphological and electronic structures investigation of Au NPs prepared at different pH values is reported. The dependence of the localized surface plasmon resonance wavelength and electronic structure with size was determined by combining transmission electron microscopy, and various spectroscopic methods led by X-ray absorption spectroscopy. The X-ray absorption experiments evidenced that the citrate-stabilized Au NPs bulk electronic structure remains intact over a broad range of pHs, and changes were detected resulting from differences in NPs surface terminations.

Brownness of organics in anthropogenic biomass burning aerosols over South Asia

Abstract. In South Asia, biomass is burned for energy and waste disposal, producing brown carbon (BrC) aerosols whose climatic impacts are highly uncertain. To assess these impacts, a real-world understanding of BrC's physio-optical properties is essential. For this region, the order-of-magnitude variability in BrC's spectral refractive index as a function of particle volatility distribution is poorly understood. This leads to oversimplified model parameterization and subsequent uncertainty in regional radiative forcing. Here we used the field-collected aerosol samples from major anthropogenic biomass activities to examine the methanol-soluble BrC optical properties. We show a strong relation between the absorption strength, wavelength dependence, and thermo-optical fractions of carbonaceous aerosols. Our observations show strongly absorbing BrC near the Himalayan foothills that may accelerate glacier melt, further highlighting the limitations of climate models where variable BrC properties are not considered. These findings provide crucial inputs for refining climate models and developing effective regional strategies to mitigate BrC emissions.

Developing a novel evaluation technique of Raman spectra for PAN-based carbon fibers using dependence of excitation wavelength and differential spectra

Developing a novel evaluation technique of Raman spectra for PAN-based carbon fibers using dependence of excitation wavelength and differential spectra

Astrometric Redshifts of Supernovae

Differential Chromatic Refraction (DCR) is caused by the wavelength dependence of our atmosphere’s refractive index, which shifts the apparent positions of stars and galaxies and distorts their shapes depending on their spectral energy distributions. While this effect is typically mitigated and corrected for in imaging observations, we investigate how DCR can instead be used to our advantage to infer the redshifts of supernovae from multiband, time-series imaging data. We simulate Type Ia supernovae in the proposed Vera C. Rubin Observatory Legacy Survey of Space and Time Deep Drilling Field, and evaluate astrometric redshifts. We find that the redshift accuracy improves dramatically with the statistical quality of the astrometric measurements as well as with the accuracy of the astrometric solution. For a conservative choice of a 5 mas systematic uncertainty floor, we find that our redshift estimation is accurate at z < 0.6. We then combine our astrometric redshifts with both host-galaxy photometric redshifts and supernovae photometric (light-curve) redshifts and show that this considerably improves the overall redshift estimates. These astrometric redshifts will be valuable, especially since Rubin will discover a vast number of supernovae for which we will not be able to obtain spectroscopic redshifts.