Optical Spectroscopic Studies Research Articles

First-principles molecular dynamics of exciton-driven initial stage of plasma phase transition in warm dense molecular nitrogen.

Understanding the properties of molecular nitrogen N2 at extreme conditions is the fundamental problem for atomistic theory and the important benchmark for the capabilities of first-principles molecular dynamics (FPMD) methods. In this work, we focus on the connection between the dynamics of ions and electronic excitations in warm dense N2. The restricted open-shell Kohn-Sham method gives us the possibility to reach relevant time and length scales for FPMD modeling of an isolated exciton dynamics in warm dense N2. Wannier localization sheds light on the corresponding mechanisms of covalent bond network rearrangements that stand behind polymerization kinetics. FPMD results suggest a concept of energy transfer from the thermal energy of ions into the internal energy of polymeric structures that form in warm dense N2 at extreme conditions. Our findings agree with the thermobaric conditions for the onset of absorption in the optical spectroscopy study of Jiang et al. [Nat. Commun. 9, 2624 (2018)].

A proton-coupled electron transfer process from functionalized carbon dots to molecular substrates: the role of pH.

Multiple electron and proton transfers in nanomaterials pose significant demands and challenges across the various fields such as renewable energy, chemical processes, biological applications, and photophysics. In this context, pH-responsive functional group-enriched carbon dots (C-Dots) emerge as superior proton-coupled electron transfer (PCET) agents owing to the presence of multiple functional groups (-COOH, -NH2, and -OH) on the surface and redox-active sites in the core. Here, we elucidate the 2e-/2H+ transfer ability of carboxyl-enriched C-Dots (C-Dot-COOH) and amine-enriched C-Dots (C-Dot-NH2) with molecular 2e-/2H+ acceptor (benzoquinone, BQ) as a function of pKa, facilitated by the formation of new O-H bonds. The ground state and excited state pKa values of different functional groups on the surface of C-Dots are determined using steady-state absorbance and photoluminescence (PL) spectroscopy. The optical spectroscopy and electrochemical studies are employed to comprehend the influence of the surface and core of C-Dots on the proton and electron transfer processes as a function of pH. The cyclic voltammetry analysis reveals a standard Nernstian shift in E1/2 per pH unit of 30 mV, indicating that the functionalized C-Dots hold promise as candidates for the 2e-/2H+ transfer process. The calculated bond dissociation free energy (BDFE) of the electroactive O-H/N-H bonds provides a more nuanced and detailed understanding of PCET thermodynamic landscapes. These findings underscore the potential of nanoscale functionalized C-Dots for facilitating multiple PCET reactions in future energy technologies.

Dynamics of charged and neutral silicon-vacancy color centers in electron-irradiated 28Si-doped single crystal chemical vapor deposition diamond upon annealing: Optical spectroscopy study

Diamond synthesis with silicon-vacancy (SiV) color centers is of high interest to nanophotonics and optical quantum technologies. The methods to control and/or maximize concentration of Si atoms incorporated in diamond lattice, and coupled to vacancies, together with improving crystallinity of diamond structure, are in demand. Here, we studied the effect of heat treatment of electron-irradiated single crystal CVD diamond doped with 28S isotope, on evolution of the neutral SiV0 and negatively charged SiV− centers. The crystal subjected to stepwise annealing at temperatures Tann from 200 °C to 1640 °C has been analyzed with photoluminescence (PL) and optical absorption spectroscopies at room and low-temperature (T = 5 K). We found a complex non-monotonous behavior of SiV0 and SiV− intensity both in absorption and PL, with sharp rise at Tann > 600 °C, reaching a maximum concentration peak, decline at 850 °C, and a repeated elevation to higher Tann, reflecting creation and annihilation processes of these defects. Moreover, we detected a group of seven lines of a Si-related defect in the range 828–871 nm, which strongly correlate with annealing dynamics of the SiV− and, especially, of SiV0 centers, and estimated the isotope spectral shift. In parallel, dynamics of other optical centers such as NV, R11 and GR1, in course of the annealing is traced. The controlled annealing opens the way to preparation of the SiV color centers with optimized optical properties, promising for quantum technologies.

Synthesis and Effect of MgSO4 co-doping on the Optical, IR, and Raman Spectroscopic Studies of Eu3+-Doped Alkaline Silica Borate Glasses Produced with SLS Glass as a Silica Source

Synthesis and Effect of MgSO4 co-doping on the Optical, IR, and Raman Spectroscopic Studies of Eu3+-Doped Alkaline Silica Borate Glasses Produced with SLS Glass as a Silica Source

Extended Kataura plot of single-walled carbon nanotubes and on-demand fabrication of mixed-dimensional heterostructures

We present a comprehensive optical spectroscopic study on air-suspended single-walled carbon nanotubes (SWNTs) with diameters ranging from 1.7 nm to 3.4 nm and at higher-order optical transitions, a previously inaccessible regime. We establish an atlas of resonant radial breathing modes (RBMs) for more than 100 new SWNTs in this unknown regime, thus significantly extending the RBM dataset in Kataura plot and enhancing our knowledge of SWNTs. Additionally, we develop an innovative transfer technique for manipulating individual SWNTs of known chiralities (determined by optical spectroscopies) by integrating a polarization imaging technique with the conventional van der Waals (vdW) dry transfer. The unprecedented spatial and structural control of this technique enables a deterministic fabrication and integration of a variety of novel mixed-dimensional vdW heterostructures that were considered unachievable before. Our work significantly extends RBM dataset of SWNT Kataura plot and represents a huge advancement towards controlled fabrication and integration of mixed-dimensional vdW heterostructures encompassing one-dimensional vdW materials.

Simultaneous Far-ultraviolet and Near-ultraviolet Observations of T Tauri Stars with UVIT/AstroSat: Probing the Accretion Process in Young Stars

We present results from simultaneous far-ultraviolet (FUV) and near-ultraviolet (NUV) observations of T Tauri stars (TTSs) in the Taurus molecular cloud with UVIT/AstroSat. This is the very first UVIT study of TTSs. From the spectral energy distribution of TTSs from FUV to IR, we show that classical TTSs (CTTSs) emit significantly higher UV excess compared to weak-line TTSs (WTTSs). The equivalent blackbody temperatures corresponding to the UV excess in CTTSs (>104 K) are also found to be relatively higher than those in WTTSs (<9250 K). From the UV excess, we have reclassified two WTTSs (BS Tau and V836 Tau) as CTTSs, which has been supported by the follow-up optical spectroscopic study using the Himalayan Chandra Telescope, showing strong Hα line emission. We find that CTTSs show strong excess emission in both the FUV (>107) and NUV (>103) bands, while WTTSs show strong excess only in the FUV (≲105), suggesting that excess emission in the NUV can be used as a tool to classify the TTSs. We also find a linear correlation between UV luminosity (a primary indicator of mass accretion) and Hα luminosity (a secondary indicator of mass accretion) with a slope of 1.20 ± 0.22 and intercept of 2.16 ± 0.70.

Comprehensive study of optical contrast, reflectance, and Raman spectroscopy of multilayer graphene

Graphene research has developed quite rapidly partially because even a monatomic layer can be visualized with a conventional optical microscope. Although optical properties of multilayer graphene such as optical contrast, reflectance (R), and Raman scattering have been well studied, they are studied independently and the thickness dependence is limited to a rather thin region. In this paper, the evolution of optical properties by thickness from monolayer to multilayer graphene up to 107 nm thick is studied comprehensively. The empirically known change of color of multilayer graphene is confirmed from the R, G and B intensities extracted from the optical images. It is also found that, as far as R for visible light is concerned, multilayer graphene is not necessarily considered as a layered material, and the refractive index for monolayer graphene is applicable even for the thickest multilayer graphene flake in this study. On the other hand, the layered structure and Raman scattering at each layer are essential to reproduce the G-band intensity of Raman scattering (I(G)). Not only the multiple reflection but also the interference of scattered Raman light should be considered for I(G) of multilayer graphene thicker than ∼30 nm.

Heteroatom-Promoted Polyhexagonal Saddle-Shaped Molecular Structures and their Supramolecular Coassembly with C60.

Molecules with curved architecture can exhibit unique optoelectronic properties due to the concave-convex π-surface. However, synthesizing negatively curved saddle-shaped aromatic systems has been challenging due to the internal structural strain. Herein, we report the facile synthesis of two polyhexagonal molecular systems, 1 and 2, with saddle shape geometry by judiciously varying the aromatic moiety, avoiding the harsh synthetic methods as that of heptagonal aromatic saddle systems. The unique geometry preferences of B, N, and S furnish suitable curvature to the molecules, featuring saddle shape. The saddle geometry also enables them to interact with fullerene C60 , and the supramolecular interactions of fullerene C60 with 1 and 2 modify their optoelectronic properties. Crystal structure analysis reveals that 1, with a small π-surface, forms a double columnar array of fullerenes in the solid state. In contrast, 2 with a large π-surface produces a supramolecular capsule entrapping two discrete fullerenes. The intermolecular interactions between B, N, S, and the aryl-π surface of the host and C60 guest are the stabilizing factors for creating these supramolecular structures. Comprehensive computational, optical, and Raman spectroscopic studies establish the charge transfer interactions between B-N doped heterocycle host and fullerene C60 guest.

A novel interferometry-based method to study the anisotropy and kinetics of liquid to solid transition in polymer

We propose and demonstrate a first Twin -interferometry based optical approach for studying and exploring anisotropy and directional dependent crystallization kinetic of curing polymers under isothermal condition. A commercial polymeric solution of polyvinylidene fluoride hexa-fluoropropylene (PVDF-HFP) with five different concentrations were prepared and utilised for this study. A Twin-interferometer (TIM) is designed to record the rate of shift in Michelson’s fringes caused by rate of change of optical path length of a transparent polymeric solution in two orthogonal directions during curing. Pair of interferogram referred as Twin- interferogram (TIG) is recorded for the sample of all concentration during its liquid to solid transition. An extraction approach for various crystallization parameters such as anisotropy, crystallization half-life time, constants governing the rate and dimensionality of crystallization, and their variation along distinct direction from TIM is demonstrated. The results provided by TIM are verified by a method of anisotropy annihilation and other experimental techniques includes Scanning electron microscopic (SEM), Polarising optical microscopic (POM) and Dielectric spectroscopic studies.

Defect Passivation of 2D Semiconductors by Fixating Chemisorbed Oxygen Molecules via h-BN Encapsulations.

Hexagonal boron nitride (h-BN) is a key ingredient for various 2D van der Waals heterostructure devices, but the exact role of h-BN encapsulation in relation to the internal defects of 2D semiconductors remains unclear. Here, it is reported that h-BN encapsulation greatly removes the defect-related gap states by stabilizing the chemisorbed oxygen molecules onto the defects of monolayer WS2 crystals. Electron energy loss spectroscopy (EELS) combined with theoretical analysis clearly confirms that the oxygen molecules are chemisorbed onto the defects of WS2 crystals and are fixated by h-BN encapsulation, with excluding a possibility of oxygen molecules trapped in bubbles or wrinkles formed at the interface between WS2 and h-BN. Optical spectroscopic studies show that h-BN encapsulation prevents the desorption of oxygen molecules over various excitation and ambient conditions, resulting in a greatly lowered and stabilized free electron density in monolayer WS2 crystals. This suppresses the exciton annihilation processes by two orders of magnitude compared to that of bare WS2. Furthermore, the valley polarization becomes robust against the various excitation and ambient conditions in the h-BN encapsulated WS2 crystals.

Valence state conversion of Mn ions in Li2O–ZnO-GeO2 glass-ceramics: Spectral, structural, ESR and XRF studies

Lithium-zinc-germanate glass-ceramics doped with Mn ions are synthesized by volume crystallization method. Structural studies show nucleation of different forms of lithium germanate crystals depending on the isothermal treatment regime of the initial glass. With the increase of the heat treatment temperature and the lithium content in the initial glass, the [GeO4] /[GeO6] ratio in the nucleated crystalline phases increases. The initial distribution of Mn2+/Mn3+/Mn4+ is defined by the Li2O/ZnO ratio in the glass composition: the ratio growth increases the contribution of Mn4+ over the Mn2+ and Mn3+. Low-temperature heat treatment of initial glass leads to uprise of intense red emission of Mn4+ ions in the octahedral environment. High-temperature heat treatment leads to occurrence of intense green emission related to Mn2+ ions in a tetrahedral environment. Discussions on all transformations of symmetry, the crystal field strength of Mn ions’ environment and their valence state based on the results of optical spectroscopy, ESR and XRF studies are provided. The maximum quantum yield of red luminescence is 61%, and of green luminescence is 23%. The synthesized glass-ceramics can be used as a luminescent converter of the UV LED radiation with the maximum energy efficiency of 20%.

Discovery of Kiloparsec-scale Semirelativistic Fe Kα Complex Emission in NGC 5728

We present Chandra ACIS-S imaging spectroscopy results of the extended (1.″5–8″, 300–1600 pc) hard X-ray emission of NGC 5728, the host galaxy of a Compton-thick active galactic nucleus. We find spectrally and spatially resolved features in the Fe Kα complex (5.0–7.5 keV) redward and blueward of the neutral Fe line at 6.4 keV in the extended narrow-line region bicone. A simple phenomenological fit of a power law plus Gaussians gives a significance of 5.4σ and 3.7σ for the red and blue wings, respectively. Fits to a suite of physically consistent models confirm a significance of ≥3σ for the red wing. The significance of the blue wing may be diminished by the presence of rest-frame highly ionized Fe xxv and Fe xxvi lines (1.4σ–3.7σ range). A detailed investigation of the Chandra ACIS-S point-spread function and comparison with the observed morphology demonstrates that these red and blue wings are radially extended (∼5″, ∼1 kpc) along the optical bicone axis. If the wing emission is due solely to redshifted and blueshifted high-velocity neutral Fe Kα, then the implied line-of-sight velocities are +/− ∼0.1c, and their fluxes are consistent with being equal. A symmetric high-velocity outflow is then a viable explanation. This outflow has deprojected velocities ∼100 times larger than the outflows detected in optical spectroscopic studies, potentially dominating the kinetic feedback power.

Spectroscopic analysis of hot, massive stars in large spectroscopic surveys with de-idealized models

ABSTRACT Upcoming large-scale spectroscopic surveys with e.g. WEAVE (William herschel telescope Enhanced Area Velocity Explorer) and 4MOST (4-metre Multi-Object Spectroscopic Telescope) will provide thousands of spectra of massive stars, which need to be analysed in an efficient and homogeneous way. Usually, studies of massive stars are limited to samples of a few hundred objects, which pushes current spectroscopic analysis tools to their limits because visual inspection is necessary to verify the spectroscopic fit. Often uncertainties are only estimated rather than derived and prior information cannot be incorporated without a Bayesian approach. In addition, uncertainties of stellar atmospheres and radiative transfer codes are not considered as a result of simplified, inaccurate, or incomplete/missing physics or, in short, idealized physical models. Here, we address the question of ‘How to compare an idealized model of complex objects to real data?’ with an empirical Bayesian approach and maximum a posteriori approximations. We focus on application to large-scale optical spectroscopic studies of complex astrophysical objects like stars. More specifically, we test and verify our methodology on samples of OB stars in 30 Doradus region of the Large Magellanic Clouds using a grid of fastwind model atmospheres. Our spectroscopic model de-idealization analysis pipeline takes advantage of the statistics that large samples provide by determining the model error to account for the idealized stellar atmosphere models, which are included into the error budget. The pipeline performs well over a wide parameter space and derives robust stellar parameters with representative uncertainties.

Understanding the Magnetic Activity of M Dwarfs: Optical and Near-Infrared Spectroscopic Studies

We present here preliminary results of stellar activities on three active M dwarfs having strong magnetic fields using optical and Near-Infrared (NIR) (0.38 μm − 2.5 μm) spectroscopic observational data using HFOSC on the 2-m HCT and TANSPEC on the 3.6-m DOT. The sample includes new observations of AD Leo, EV Lac, and Stkm2-809 M dwarfs, including published literature values of 89 M dwarfs. To understand the magnetic field activity on those dwarfs, we used the equivalent widths of spectral features Ca IRT triplet (0.850 μm, 0.854 μm, 0.866 μm), which are generally chromospheric and coronal indicators in M dwarfs, and investigate the correlation between those line strengths with Rossby number, which is defined as the ratio of rotation period (Prot) to convective turnover time (τconv). We find a strong correlation between the equivalent widths of Ca IRT b and Ca IRT c and Rossby number (R0). The correlation shows an increasing trend of equivalent widths of those lines with decreasing R0, and saturation of the equivalent widths of those at lower R0 ≤0.1. To estimate R0, we estimate the rotation periods of three observed M dwarfs in our sample from TESS data, and in the case of other M dwarfs, we used the literature values. Interestingly, in TESS light curves of AD Leo, EV Lac, and Stkm2-809 M dwarfs, we find several flare events. We estimated the bolometric flared energy in a range of 1034 to 1037 erg, which is in the superflare range (more than 1032 erg). We estimate the highest flared energy of 1.22 × 1037 erg for EV Lac in TESS sector 57. To produce such kind of high superflare event, we have estimated the required magnetic field strength of 10.53 kG, which will have an impact on the life habitability of planets around such M dwarfs.

Sixty years of electrochemical optical spectroscopy: a retrospective.

Sixty years ago, Reddy, Devanatan, and Bockris performed the first in situ electrochemical ellipsometry experiment, which ushered in a new era in the study of electrochemistry, using optical spectroscopy. After six decades of development, electrochemical optical spectroscopy, particularly electrochemical vibrational spectroscopy, has advanced from a phase of immaturity with few methods and limited applications to a phase of maturity with excellent substrate generality and significantly improved resolutions. Here, we divide the development of electrochemical optical spectroscopy into four phases, focusing on the proof-of-concept of different electrochemical optical spectroscopy studies, the emergence of plasmonic enhancement-based electrochemical optical spectroscopic (in particular vibrational spectroscopic) methods, the realization of electrochemical vibrational spectroscopy on well-defined surfaces, and the efforts to achieve operando spectroelectrochemical applications. Finally, we discuss the future development trend of electrochemical optical spectroscopy, as well as examples of new methodology and research paradigms for operando spectroelectrochemistry.

(Invited) Towards GaN Passivation: Identification of GaN Surface/Interface States

GaN has been emerging as the next technological semiconductor after silicon and has already secured its superiority in the niche of power electronics with a rapidly growing interest since the advent of electric vehicles. To enable GaN to concur more microelectronic applications, one major barrier has yet to be surpassed. Rather limited control has so far been achieved over the density of GaN interface states. To achieve it, native and process-induced surface states need to be fully identified. Photoluminescence (PL) has been the most commonly used method in the study of GaN defects, and it typically shows a wide sub-bandgap peak centered at 2.2 eV that has been called the yellow luminescence (YL) band. Despite 30 years of studies, the debate as to whether this is a bulk or surface defect has not been settled. Present deep level characterization methods have not provided clear enough evidence. Theoretical studies attempted to associate this luminescence with various bulk defects, e.g., Ga-vacancies, O or O-C complexes,[1] while various optical spectroscopy studies, point to a surface origin.[2]Here, we report results of using an optical spectroscopy method based on surface photovoltage before and after a mild anneal in vacuum. The method is capable of showing the energy distribution of charge density trapped in surface states and thus of monitoring changes thereof. Using the method in air on untreated GaN reveals two peaks over the same ranges of the yellow and blue peaks observed by PL. After a mild anneal at 170 C for 24 hrs in vacuum, the “yellow” charge density peak was absent. Exposure to air was then observed to fully restore the “yellow” charge density peak. This observation clearly points to the involvement of an airborne molecule, a constituent of air, as the source for charge in the yellow-luminescence-related state. If this deep level were a bulk defect, it would not be able to interact with air. This observed interaction with air thus provides a first direct evidence that the yellow luminescence-related defect is a surface state. Experiments of controlled exposure to the various air constituents to identify the related airborne molecule are currently ongoing. The same method is now used in a search for passivation method for this surface state.The method we use is based on the following model. Illumination using sub-band gap photon energies excites electrons from the surface states over the surface potential barrier, consequently, reducing the surface band bending, and this change is observed as photovoltage (Fig. 1). We have already shown how this photovoltage can be used for calculation of the surface charge distribution in GaN HEMT.[3] In the case of bulk crystal, the model is slightly different, and a quantitative relation may be obtained between the measured photovoltage and the surface state charge distribution. Quantitative calculation requires knowledge of the surface band bending in equilibrium, which may not always be reliably obtained. However, when the spectrum is acquired using low photon flux, assuring the change in the band bending is small compared with the equilibrium band bending the surface charge density is practically relative to the derivative of the photovoltage, and thus, qualitative distribution may be obtained.[4]Figure 2 exemplifies the use of the model presented here to obtain a qualitative charge density spectrum. It shows surface charge density obtained using the model from the photovoltage spectrum shown as inset.This method is then used in Fig. 3 to compare three spectra of the same sample: In air (red), in vacuum (green) - the yellow peak is slightly reduced, and after heating up to 450 K for 24 h in vacuum (blue) - the yellow peak is practically gone.These results suggest that the charge in the yellow-luminescence-related state is contributed by a non-inert constituent of air, and this interaction may not be possible unless this state is a surface state. In the talk, preliminary results on the chemical identity of this air constituent will be presented.[1] Van de Walle et al., Microscopic origins of surface states on nitride surfaces, J. Appl. Phys. 101, 081704 (2007).[2] Shalish et al., Yellow luminescence and related deep levels in unintentionally doped GaN films, Phys. Rev. B 59, 9748 (1999).[3] Turkulets et el., Surface states in AlGaN/GaN high electron mobility transistors: Quantitative energetic profiles and dynamics of the surface Fermi level, Appl. Phys. Lett. 115, 023502 (2019).[4] Turkulets et al. The GaN(0001) yellow-luminescence-related surface state and its interaction with air. Surfaces and Interfaces 38, 102834 (2023). Figure 1

Optical emission spectroscopy of vanadium cathodic arc plasma at different nitrogen pressure

Optical emission spectroscopy studies of vanadium plasma in a cathodic-arc discharge in a nitrogen atmosphere have been carried out. Spectral lines of neutral atoms and ions of the cathode material V, V1+, and V2+, and nitrogen N2 and N2+ were observed in the discharge plasma. Analysis and comparison of the intensity of vanadium and nitrogen spectral lines as a function of nitrogen pressure showed that in vacuum excited ions V2+ and V+ are registered, with increasing pressure, the lines V+*, N2*, and N2+* are observed, and at pressures above 0.5 Pa, the neutral vanadium lines are additionally registered. The electron temperature of Te decreases from 5.9 to 3–4 eV with increasing pressure. Studies of cross-sectional scanning electron microscopy images of VN coatings deposited at different nitrogen pressures have shown that a dense, homogeneous, fine-grained microstructure is formed in the coating when the number of neutral V in the plasma is low, while in the presence of a large number of neutrals, the coating structure changes to a dense structure with columnar growth.

Synchrotron X-Ray Topography Studies for Defect Formation at the Early Stage of PVT-Grown 4H-SiC Crystals

Silicon Carbide (SiC), typically 4H-SiC, is replacing conventional silicon materials for high power and high frequency applications due to its excellent electrical and thermal properties [1]. However, high quality SiC wafers with low defect density are still in urgent need for automotive and energy saving applications. SiC wafers are obtained from bulk growth by physical vapor transport (PVT) method and considerable efforts have been expended to optimize growth process to lower defect densities. One major approach is the study of initial stages of crystal growth as most defects are nucleated at this stage and propagate into the boule. Ailihumaer et al [2] demonstrated the behaviors of threading edge dislocations (TEDs), threading screw dislocations (TSDs)/threading mixed dislocations (TMDs), and basal plane dislocations (BPDs) across the seed/newly grown layer interface in PVT-grown 4H-SiC. Sanchez et al [3] revealed the nucleation of TEDs and TSDs at the initial growth stage in PVT-grown SiC.However, more detailed investigations are still in demand for PVT grown 4H-SiC crystals during initial stage of growth. This study investigates 4° off-axis 4H-SiC wafers with several hundred microns of initial-stage growth PVT method. Synchrotron X-ray topography (SXRT) technique is employed and shows dramatically modified defect distribution across the seed/newly grown layer interface (Figure 1). The formation of Shockley stacking fault starting at initial stage of crystal growth is suggested as partial dislocations running along <11-20> directions on basal plane are observed to form rhombus shapes (Figure 2). Prismatic slip is observed to take place near the wafer edges and prismatic dislocations undergo cross slip to form unique dislocation configurations. A statistical analysis on defect changes across the seed/newly grown layer is being carried out and the results will be reported. These results will be complemented by observations from Nomarski optical microscopy (NOM) and Raman Spectroscopy studies to propose the formation mechanism of defects across the seed/newly grown layers.

Structural, optical, dielectric relaxation, complex impedance and modulus spectroscopic studies of pure and glutamic acid doped potassium dihydrogen phosphate

Structural, optical, dielectric relaxation, complex impedance and modulus spectroscopic studies of pure and glutamic acid doped potassium dihydrogen phosphate

Mechanistic insights into excited-state palladium catalysis for C–S bond formations and dehydrogenative sulfonylation of amines

Photocatalytic selective C(sp3)–H activation/cross-coupling reactions are appealing in organic synthesis. In this manuscript, we describe the development of photoexcited-state Pd-catalyzed dehydrogenative β-sulfonylation reactions using amines and aryl sulfonyl chlorides via intermolecular hydrogen atom transfer and C−S cross-coupling processes at room temperature. The transformation can be achieved by the direct generation of two distinct Pd-radical hybrid species and their capability to promote two different reactivities from Pd(0) and aryl sulfonyl chlorides, allowing for the efficient conversion of readily available amines into stable sulfonyl-substituted enamines at room temperature. The in-depth experimental, computational, and transient optical spectroscopic study and catalytic applications of a dehydrogenative functionalization event provide evidence for both static and dynamic quenching, as well as inner-sphere and outer-sphere mechanisms.