near-IR Region Research Articles

Back electron transfer rates determine the photoreactivity of donor-acceptor stilbene complexes in a macrocyclic host.

Host-guest 2 : 1 complexation of photoreactive alkene guests improves the selectivity of [2 + 2] photodimerizations by templating alkene orientation prior to irradiation. Host-guest chemistry can also provide 1 : 1 : 1 complexes through the inclusion of electronically complementary donor and acceptor guests, but the photoreactivity of such complexes has not been investigated. We imagined that such complexes could enable selective cross-[2 + 2] photocycloadditions between donor and acceptor stilbenes. In pursuit of this strategy, we investigated a series of stilbenes and found 1 : 1 : 1 complexes with cucurbit[8]uril that exhibited charge-transfer (CT) absorption bands in the visible and near-IR regions. Irradiation of the CT band of an azastilbene, 4,4'-stilbenedicarboxylate, and cucurbit[8]uril ternary complex led to a selective cross-[2 + 2] photocycloaddition, while other substrate pairs exhibited no productive chemistry upon CT excitation. Using transient absorption spectroscopy, we were able to understand the variable photoreactivity of different stilbene donor-acceptor complexes. We found that back electron transfer following CT excitation of the photoreactive complex is positioned deep in the Marcus inverted region due to electrostatic stabilization of the ground state, allowing [2 + 2] to effectively compete with this relaxation pathway. Control reactions revealed that the cucurbit[8]uril host not only serves to template the reaction from the ground state, but also protects the long-lived radical ions formed by CT from side reactions. This protective role of the host suggests that donor-acceptor host-guest ternary complexes could be used to improve existing CT-initiated photochemistry or access new reactivity.

Оптические свойства нановискеров Cu-=SUB=-2-=/SUB=-O

The optical properties of Cu2O nanowhiskers grown by the liquid method with material deposition in an electric field have been studied. The spectral lines forbidden by the selection rules for perfect Cu2O crystals were found in the Raman spectra. The nature of related phonon states is analyzed. In the photoluminescence spectra in the red and near-IR regions, broad bands of defective origin are observed. It was found that the presence of a band at 650 nm (1.9 eV) is a specific feature of the photoluminescence of nanowhiskers. Its properties are studied and possible radiation mechanisms are discussed. In the intrinsic absorption region of nanowhiskers, the photoluminescence band at 572 nm (2.17 eV) associated with band−band transitions is detected. At a low excitation level, the emission of a free exciton n = 1 of the yellow exciton series is observed with simultaneous emission of an optical phonon.

Two-photon absorption and triplet excited state quenching of near-IR region aza-BODIPY photosensitizers via a triphenylamine moiety despite heavy bromine atoms.

Aza-BODIPY compounds with methoxy groups at -3 and -5 and triphenylamine moieties at -1 and -7 positions with and without heavy bromine atoms at -2 and -6 positions have been designed and synthesized. The chemical structures of the novel compounds were fully characterized using 1H NMR, 13C NMR, FTIR, and HRMS-TOF-ESI techniques. Steady-state absorption and emission features were investigated to analyze ground-state interactions. The effects of triphenylamine moieties and bromine atoms on charge transfer dynamics and two-photon absorption (TPA) properties were investigated using femtosecond transient absorption spectroscopy measurements and open-aperture (OA) Z-scan experiments, respectively. Contrary to popular belief, the compound containing heavy bromine atoms and triphenylamine moieties did not demonstrate any triplet transition. Since the triphenylamine moiety has high electron-donating properties and a long conjugation length, it exhibited intramolecular charge transfer (ICT) features from electron-donating moieties to the aza-BODIPY core. Additionally, it is concluded that the excited-state lifetime is shortened in the presence of a bromine atom with triphenylamine moieties. This result is rather interesting since the triplet excited state is quenched by the triphenylamine moiety despite the presence of a heavy bromine atom. The performed OA Z-scan experiments revealed that the aza-BODIPY compound containing bromine atoms has a higher TPA cross-section value (116 GM) due to efficient intramolecular charge transfer compared to that without bromine atoms (89 GM). Additionally, in the theoretical calculations, it was found that the charge transfer percentage (CT%) was the strongest in compounds containing bromine atoms.

PLS-R Calibration Models for Wine Spirit Volatile Phenols Prediction by Near-Infrared Spectroscopy.

Near-infrared spectroscopic (NIR) technique was used, for the first time, to predict volatile phenols content, namely guaiacol, 4-methyl-guaiacol, eugenol, syringol, 4-methyl-syringol and 4-allyl-syringol, of aged wine spirits (AWS). This study aimed to develop calibration models for the volatile phenol’s quantification in AWS, by NIR, faster and without sample preparation. Partial least square regression (PLS-R) models were developed with NIR spectra in the near-IR region (12,500–4000 cm−1) and those obtained from GC-FID quantification after liquid-liquid extraction. In the PLS-R developed method, cross-validation with 50% of the samples along a validation test set with 50% of the remaining samples. The final calibration was performed with 100% of the data. PLS-R models with a good accuracy were obtained for guaiacol (r2 = 96.34; RPD = 5.23), 4-methyl-guaiacol (r2 = 96.1; RPD = 5.07), eugenol (r2 = 96.06; RPD = 5.04), syringol (r2 = 97.32; RPD = 6.11), 4-methyl-syringol (r2 = 95.79; RPD = 4.88) and 4-allyl-syringol (r2 = 95.97; RPD = 4.98). These results reveal that NIR is a valuable technique for the quality control of wine spirits and to predict the volatile phenols content, which contributes to the sensory quality of the spirit beverages.

Efficient Achromatic Broadband Focusing and Polarization Manipulation of a Novel Designed Multifunctional Metasurface Zone Plate.

In this paper, comprehensively utilizing the diffraction theory and electromagnetic resonance effect is creatively employed to design a multifunctional metasurface zone plate (MMZP) and achieve the control of polarization states, while maintaining a broadband achromatic converging property in a near-IR region. The MMZP consists of several rings with fixed width and varying heights; each ring has a number of nanofins (usually called meta-atoms). The numerical simulation method is used to analyze the intensity distribution and polarization state of the emergent light, and the results show that the designed MMZP can realize the polarization manipulation while keeping the broadband in focus. For a specific design wavelength (0.7 μm), the incident light can be converted from left circularly polarized light to right circularly polarized light after passing through the MMZP, and the focusing efficiency reaches above 35%, which is more than twice as much as reported in the literature. Moreover, the achromatic broadband focusing property of the MMZP is independent with the polarization state of the incident light. This approach broadens degrees of freedom in micro-nano optical design, and is expected to find applications in multifunctional focusing devices and polarization imaging.

The influence of the surface density of oriented nickel networks on the conducting electrode’s optical transparency

This study is part of the work on the creation of a transparent conductive coating based on oriented nanonetwork and submicron nickel fibres. It is devoted to finding the optimal values of electrical conductivity and optical transparency of the developed coating. In this work, we study the transmission spectra of oriented nickel networks on a glass substrate in the UV, visible and near-IR regions at different amounts of deposited metal. An exciting feature of the coating was discovered: in the range of 950 nm and above, there is a "bend" of the transmission spectrum downward. This bend (increased absorption of radiation in the near-IR region) is observed only in the presence of nickel nanonetwork and is not typical for a pure submicron network.

Optical-parametric-oscillation-based χ(2) frequency comb in a lithium niobate microresonator

Microresonator frequency combs based on the χ(3) nonlinearity are nowadays well understood and making their way into different applications. Recently, microresonator frequency combs based on the χ(2) nonlinearity are receiving increasing attention, as they promise certain benefits, but still require further study. Here, we present the first indication of χ(2) frequency comb generation, initiated via optical parametric oscillation (OPO) in a lithium niobate mm-sized microresonator. By pumping at 532 nm with 300 µW of power, we observe 1-THz-wide comb spectra around 1064 nm with degenerate and non-degenerate states. We also show that comb generation requires signal and idler waves to be degenerate in mode numbers and how the fulfillment of this condition can be identified from the temperature tuning curves. The results demonstrate the potential to directly generate frequency combs via OPO beyond 3 μm wavelengths in the mid-IR by puming in the near-IR region.

Solid-State Structures and Photoluminescence of Lamellar Architectures of Cu(I) and Ag(I) Paddlewheel Clusters with Hydrogen-Bonded Polar Guests.

Two hexanuclear paddlewheel-like clusters appending six carboxylic-acid pendants have been isolated with the inclusion of polar solvent guests: [Cu6(Hmna)6]·7DMF (1·7DMF) and [Ag6(Hmna)6]·8DMSO (2·8DMSO), where H2mna = 2-mercaptonicotininc acid, DMF = N,N’-dimethylformamide, and DMSO = dimethyl sulfoxide. The solvated clusters, together with their fully desolvated forms 1 and 2, have been characterized by FTIR, UV–Vis diffuse reflectance spectroscopy, TG-DTA analysis, and DFT calculations. Crystal structures of two solvated clusters 1·7DMF and 2·8DMSO have been unambiguously determined by single-crystal X-ray diffraction analysis. Six carboxylic groups appended on the clusters trap solvent guests, DMF or DMSO, through H-bonds. As a result, alternately stacked lamellar architectures comprising of a paddlewheel cluster layer and H-bonded solvent layer are formed. Upon UV illumination (λex = 365 nm), the solvated hexasilver(I) cluster 2·8DMSO gives intense greenish-yellow photoluminescence in the solid state (λPL = 545 nm, ΦPL = 0.17 at 298 K), whereas the solvated hexacopper(I) cluster 1·7DMF displays PL in the near-IR region (λPL = 765 nm, ΦPL = 0.38 at 298 K). Upon complete desolvation, a substantial bleach in the PL intensity (ΦPL < 0.01) is observed. The desorption–sorption response was studied by the solid-state PL spectroscopy. Non-covalent interactions in the crystal including intermolecular H-bonds, CH⋯π interactions, and π⋯π stack were found to play decisive roles in the creation of the lamellar architectures, small-molecule trap-and-release behavior, and guest-induced luminescence enhancement.

Near-Infrared Quantum Cascade Lasers Designed with van der Waals Materials

Quantum cascade lasers (QCLs) constitute a leading source of coherent radiation in the mid-IR region. However, their performance outside this region remains unsatisfactory. Indeed, there are currently no QCLs in the near-IR region. Here, we propose that a superlattice of atomically thin layers held together by van der Waals forces may operate near room temperature as a compact and powerful near-IR QCL emitting at a wavelength of $1.66\phantom{\rule{0.2em}{0ex}}\ensuremath{\mu}\mathrm{m}$. It can compress over 100 stages within $0.5\phantom{\rule{0.2em}{0ex}}\ensuremath{\mu}\mathrm{m}$. The electric field required for operation is about $3\ifmmode\times\else\texttimes\fi{}{10}^{6}\phantom{\rule{0.2em}{0ex}}{\mathrm{V~cm}}^{\ensuremath{-}1}$, while the lasing threshold current density is about $22.4\phantom{\rule{0.2em}{0ex}}{\mathrm{kA~cm}}^{\ensuremath{-}2}$ depending on parameters. Rate-equation analysis reveals that the peak power per unit volume can reach over $0.1\phantom{\rule{0.2em}{0ex}}\mathrm{mW}\phantom{\rule{0.2em}{0ex}}\ensuremath{\mu}{\mathrm{m}}^{\ensuremath{-}3}$ in cw operation. Unlike existing QCLs, our device is $p$-type working with holes.

Polycyclic aromatic hydrocarbon-substituted push-pull chromophores: an investigation of optoelectronic and nonlinear optical properties using experimental and theoretical approaches.

A series of new push–pull chromophores were synthesized in moderate to very high yields (65%–97%) by treating TCNE and TCNQ with alkynes substituted by electron-rich diethylaniline and polycyclic aromatic hydrocarbons. Some of the chromophores exhibit strong intramolecular charge-transfer bands in the near-IR region with λmax values between 695 and 749 nm. With the help of experimental and theoretical analysis, it is concluded that the trend in λ max values is affected by PAH substituents sterically, not electronically. Steric constraints led to the increased dihedral angles, reducing conjugation efficiencies. The absorption properties of push-pull compounds have been investigated in solvents possessing different polarities. All chromophores exhibited positive solvatochromism. As an additional proof of efficient charge-transfer in push–pull chromophores, quinoid character (dr) values were predicted using calculated bond lengths. Remarkably, substantial dr values (0.045–0.049) were predicted for donor diethylaniline rings in all compounds. The effects of various polycyclic aromatic hydrocarbons on optical and nonlinear optical properties were also studied by computational methods. Several parameters, such as band gaps, Mulliken electronegativity, chemical hardness and softness, dipole moments, average polarizability, first hyperpolarizability, were predicted for chromophores at the B3LYP/6-31++G(d,p) level of theory. The predicted first hyperpolarizability β(tot) values vary between 198 to 538 × 10–30 esu for the reported push–pull chromophores in this study. The highest predicted β(tot) value in this study is 537.842 × 10–30 esu, 8150 times larger than the predicted β(tot) value of benchmark NLO material urea, suggests possible utilization of these chromophores in NLO devices. The charge-transfer character of the synthesized structures was further confirmed by HOMO-LUMO depictions and electrostatic potential maps.

Simultaneously surface- and edge-emitting plasmonic laser operating in the near-infrared region

Near-infrared (IR) plasmonic lasers are a crucial stepping stone toward building sustainable nanoscale optoelectronic circuitry. Nevertheless, plasmonic lasers are at their infancy, and optimized designs for improved characteristics and novel applications are essential. We design an efficient plasmonic laser that simultaneously works in the near-IR region as a surface- and edge-emitting laser with collimated far-field beam pattern. While the surface emission is enhanced with a planar two-dimensional (2D) metal nanohole array (NHA) interfaced with the gain medium, the edge emission is enhanced with a 2D array of grooves. Additionally, 2D NHA or grooves on the metal layer collimate the far-field beam pattern of surface emission in the forward and backward direction, respectively. By contrast, the edge emission diverges at the far-field with an angle-resolved beam pattern from -90° to 90°. We propose and design a plasmonic collimator that uses groove-aperture nanostructures carved on gold slabs mounted on the laser facet to collimate the far-field beam patterns for edge emission. We determine the optimal dimensional parameters of the collimator. The optimized collimator produces a far-field beam that is focused to a narrow spot of 3° × 4° only.

Infrared spectroscopy of the protonated HCl dimer and trimer.

The protonated HCl dimer and trimer complexes were prepared by pulsed discharges in supersonic expansions of helium or argon doped with HCl and hydrogen. The ions were mass selected in a reflectron time-of-flight spectrometer and investigated with photodissociation spectroscopy in the IR and near-IR regions. Anharmonic vibrational frequencies were computed with VPT2 at the MP2/cc-pVTZ level of theory. The Cl-H stretching fundamentals and overtones were measured in addition to stretch-torsion combinations. VPT2 theory at this level confirms the proton-bound structure of the dimer complex and provides a reasonably good description of the anharmonic vibrations in this system. The trimer has a HCl-HClH+-ClH structure in which a central chloronium ion is solvated by two HCl molecules via hydrogen bonding. VPT2 reproduces anharmonic frequencies for this system, including several combinations involving core ion Cl-H stretches, but fails to describe the relative band intensities.

Polarization enhancement of linearly polarized light through foggy environments at UV-NIR wavelengths.

Wavelength is an essential factor affecting polarization propagation. We investigate the polarization persistence of linearly polarized light from ultraviolet to near-IR in foggy environments. Certain spectral bands, from ultraviolet to IR wavelengths that exhibit lower path loss, were initially selected. Using polarization-tracking Monte Carlo simulations for varying particle size, wavelength, refractive index and detection range, it is shown that linear polarization exhibits different persistence performance at different wavelengths in various foggy environments. For wet haze of 0.6 µm or 1 µm droplets, parallel polarization increases persistently as the wavelength increases, and has superior persistence in the near-IR region. For radiation fog of 5 µm or 7.5 µm droplets, parallel polarization shows superior persistence in the ultraviolet region. For advection fog of 15 µm or 45 µm droplets, parallel polarization shows a superior persistence in the ultraviolet region. It is therefore shown that changing the wavelength can improve linear polarization persistence in foggy environments.

A computational approach on engineering short spacer for carbazole-based dyes for dye-sensitized solar cells

Donor-π-linker-acceptor (D-π-A) push–pull dye molecules are most common in dye-sensitized solar cells (DSSCs) applications. Selection of dye molecules for DSSCs is based on their ability to absorb light in the visible spectrum. This can be done more efficiently by positioning the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) with respect to the conduction band of the semiconductor and the redox potential of the electrolyte, respectively. The photocurrent is manipulated by the extent of light absorption, planarity of the π-linker for efficient intramolecular charge transfer (ICT), oxidized dye reorganization energy (Λ) and dye regeneration driving force (ΔGreg). In a quest of achieving panchromatic absorption up to near-IR region, mostly electron-rich chromophores and their oligo form were used in the π-segment, but this approach led to poor ICT. In this computational analysis, we have explored the effect of electron-withdrawing (cyano (–CN)) and donating groups (methoxy (-OMe)) in three different π-segment length to understand the carbazole dyes’ suitability for DSSCs using onset wavelength (λonset), Λ, ICT and ΔGreg as the figure-of-merits.

Synthesis and characterization of AgBiS2/rGO nanocomposites: Interfacial charge transfer process

AgBiS2-rGO hybrid nano composite has been synthesized by the facile solvothermal technique. The phase formation has been identified by structural analysis which confirmed the formation of AgBiS2-rGO hybrid composite. Raman analysis ensured the presence of AgBiS2, GO and defect state of the graphene. The morphology of composite shown as flakes composed of sphere shaped structure aggregate on the rGO sheets and also well aligned crystallinity with lattice spacing of 0.28 nm of AgBiS2. The embedded AgBiS2 flakes on rGO sheets are highly favourable for fast electron transfer because of its large surface area. The absorption spectrum gradually increased in the near-IR region with the increased content of GO. Tauc plot was used to estimate the optical band gap. The impedance analysis exposed the less charge transfer resistance with the increased GO composition. These results have confirmed the formation of AgBiS2 on rGO and interaction between them.

Ultrafast Dynamics in Cu-Deficient CuInS2 Quantum Dots: Sub-Bandgap Transitions and Self-Assembled Molecular Catalysts

The photophysical properties of Cu-deficient Cu0.2In1Sx quantum dots synthesized through a facile aqueous-based procedure have been investigated. Transient absorption experiments were carried out probing in the UV–vis, near-IR, and mid-IR regions, with the aim to (i) study the photophysical properties of the quantum dots and (ii) monitor kinetics of electron transfer to a molecular catalyst. When pumping sub-bandgap transitions, negative (bleach) signals were observed that were spectrally and kinetically distinct from those observed with bandgap pump wavelengths. Herein, these distinct contributions are suggested to result from the overlapping bleaching of state filling electrons and trapped holes. Such an interpretation highlights the importance of considering the hole-contributions to the bleach for the proper determination of carrier kinetics in similar systems. A model complex of the [Fe2]-hydrogenase active site was introduced to explore the potential of the quantum dots as photosensitizers for molecular catalysts. The quantum dot photoluminescence was quenched upon catalyst addition, and direct evidence of the singly reduced catalyst was found by transient absorption in the UV–vis and mid-IR. The catalyst accepted reducing equivalents on a subpicosecond time scale upon photoexcitation of the quantum dots, despite no covalent linking chemistry being applied. This implies that charge transfer is not limited by diffusion rates, thus confirming the presence of spontaneous quantum dot and catalyst self-assembly.

Synthesis and Study of the Optical Properties of PMMA Microspheres and Opals.

Polymethylmethacrylate (PMMA) microspheres were synthesized by surfactant-free emulsion polymerization. These microspheres were used to obtain opals by the self-assembly method. Monomer and initiator quantities were varied systematically to monitor the size of PMMA microspheres. From SEM and DLS measurements, a trend was observed showing as the monomer and initiator amounts increased the average diameter of PMMA microspheres increased except when a minimum monomer amount was reached, for which the size of the microspheres remained practically constant. Diffuse reflectance spectra were processed by the Kubelka–Munk treatment to estimate the energy band gap (Eg) of the PMMA microspheres. It was found that PMMA microspheres present an indirect transition. From SEM micrographs, it is seen that PMMA opals photonic crystals are formed by microspheres in a uniform periodic face-centered cubic (fcc) array. Variable-angle specular reflectance spectra show that the opals possess a pseudo photonic band gap (PBG) in the visible and near-IR regions. Furthermore, it was found that PBGs shift towards larger wavelengths as the average diameter of the PMMA microspheres increases.

Phenacyl Phenothiazinium Salt as a New Broad-Wavelength-Absorbing Photoinitiator for Cationic and Free Radical Polymerizations.

A novel broad-wavelength-absorbing photoinitiator based on phenacyl phenothiazinium hexafluroantimonate (P-PTh) possessing both phenacyl and phenothiazine chromophoric groups was reported. P-PTh absorbs light at UV, Visible and Near-IR region. Photophysical, photochemical, and computational investigations revealed that P-PTh in solution decomposes at all wavelengths by homolytic and heterolytic cleavages and generates cationic and radical species, which could efficiently initiate cationic and free radical polymerizations. It is anticipated that the photoinitiator with such wavelength flexibility may open up new pathways in curing applications of formulations of pigment systems.

Synthesis, structure, electronic characterization, and halogenation of gold(III) phlorin complexes

The metalation chemistry of the phlorin, which is a non-aromatic tetrapyrrole macrocycle containing a single sp3-hybridized meso-carbon has remained underdeveloped, as compared to that of more traditional tetrapyrroles such as porphyrins, corroles and phthalocyanines. There have been few prior efforts to prepare metallophlorins, and those that have been reported have relied on either reduction or nucleophilic attack of parent metalloporphyrins, rather than direct metalation of freebase phlorin constructs. In this work, an alternate synthetic approach for preparation of gold(III) phlorin complexes that involves the first direct metalation of two different freebase phlorin derivatives (3H(Phl[Formula: see text] and 3H(Phl[Formula: see text] with AuBr3to produce the stable and fully isolable gold(III) phlorin complexes Au(Phl[Formula: see text] and Au(Phl[Formula: see text] is reported. The first structural characterization of a metallophlorin bearing geminal dimethyl substituents at the sp3-hybridized meso-carbon via X-ray crystallography is also reported. In addition to the preparation of Au(Phl[Formula: see text] and Au(Phl[Formula: see text], the UV-vis absorption and redox properties of these two gold(III) phlorins in comparison to those of their freebase homologues is also detailed. Notably, the metallophlorins are characterized by panchromatic absorbance profiles and intense and broad bands that span the long-visible and into the near-IR regions, as well as two fully reversible oxidation and reduction waves as probed by cyclic voltammetry. Finally, the chlorination of Au(Phl[Formula: see text] using PhI(Cl[Formula: see text] was probed and it was found that this regioslective reaction generates monochlorinated (Au(Phl[Formula: see text]Cl)) and dichlorinated (Au(Phl[Formula: see text]Cl[Formula: see text] products, which were both structurally characterized by X-ray crystallography.

Large scale self-assembly of plasmonic nanoparticles on deformed graphene templates

Hierarchical heterostructures of two-dimensional (2D) nanomaterials are versatile platforms for nanoscale optoelectronics. Further coupling of these 2D materials with plasmonic nanostructures, especially in non-close-packed morphologies, imparts new metastructural properties such as increased photosensitivity as well as spectral selectivity and range. However, the integration of plasmonic nanoparticles with 2D materials has largely been limited to lithographic patterning and/or undefined deposition of metallic structures. Here we show that colloidally synthesized zero-dimensional (0D) gold nanoparticles of various sizes can be deterministically self-assembled in highly-ordered, anisotropic, non-close-packed, multi-scale morphologies with templates designed from instability-driven, deformed 2D nanomaterials. The anisotropic plasmonic coupling of the particle arrays exhibits emergent polarization-dependent absorbance in the visible to near-IR regions. Additionally, controllable metasurface arrays of nanoparticles by functionalization with varying polymer brushes modulate the plasmonic coupling between polarization dependent and independent assemblies. This self-assembly method shows potential for bottom-up nanomanufacturing of diverse optoelectronic components and can potentially be adapted to a wide array of nanoscale 0D, 1D, and 2D materials.