Low Energy UV Research Articles

Deciphering the Effects of Different Types of Sunlight Radiation on Skin Function: A Review

Sunlight radiation is a fundamental component of our daily lives. Specifically, blue light as well as UV light appear to play a role in the development of oxidative stress, DNA damage, photoaging, and pigmentation through the chromophores in skin tissues. However, several skin problems like psoriasis, eczema, and atopic dermatitis can be avoided with short-duration exposures to low-energy blue light radiation or UV radiation. In addition, exploring the effects of blue light as well as UV radiation on skin is quite essential for the development of minimally invasive antiaging strategies and for the design of innovative cosmetic formulations in modern aesthetics and cosmetology. Thus, in this review, we present the advantages as well as the disadvantages of light radiation, with a special focus on blue light and UV radiation activity on the human skin. We also discuss the molecular action of blue light and UV radiation on human skin. Other types of light radiation are included to holistically approach the effect of light on human skin.

High reflectivity, ultraflat-spectrum chirped fiber Bragg grating written using low energy UV femtosecond pulses

Chirped fiber Bragg gratings (CFBGs) have been extensively used in applications such as ultrafast lasers, fiber sensors, and fiber communications. This work presents a comprehensive investigation of CFBG written using a 257 nm femtosecond laser and a linear chirped phase mask. The CFBG, written on a hydrogen-loaded polarization-maintaining fiber, exhibited a center wavelength of 1031.7 nm and a bandwidth of 11.97 nm. The CFBG achieved an average reflectivity of 98.2 % within its bandwidth, demonstrating an ultrahigh flatness of the reflection spectrum with a low spectral reflectivity variance of 0.00003 (σ2). The high group velocity dispersion (GVD) of 60.7 ps2 signifies its potential in fiber chirped pulse amplification systems and dispersion compensation system. Meanwhile, the fs-laser + PM writing method shows advantages of high efficiency and low energy consumption (as low as 2 nJ), owing to the high photosensitivity of the fiber to the UV band, which holds significant promise in fiber grating inscription.

Synthesis of amorphous titania nanostructures by pulsed-laser decomposition of liquid metal-organic precursor with post-annealing transformation into crystalline-layered TiO2 nanorods and nanospheres

Amorphous and non-stoichiometric titania nanoparticles and films are produced by pulsed-laser decomposition of a liquid titanium tetra-isopropoxide (TTIP) precursor bath. Nanoparticles are formed in the TTIP solution, where the submerged laser-induced plasma generates vaporized species that are rapidly quenched by the surrounding (chilled) liquid precursor. Additionally, relatively-dense films are formed on a glass substrate above the surface of the TTIP bath by vapor transport and condensation of pyrolyzed species. Interestingly, upon post-annealing at 400 °C (∼ 0.3 TM) in ambient air of the collected nanoparticles in the bath, a transformation of the amorphous non-stoichiometric titania nanoparticles occurs, producing novel anatase-TiO2 morphologies, such as crystalline-layered nanorods and onion-like nanospheres.Chemical analysis of the as-synthesized particles and films shows they are rich in oxygen and carbon relative to TiO2. As a result, an amorphous-to-crystalline phase transformation during heat treatment in air starts at the surfaces of the nanoparticles, irrespective of their morphologies, and propagates into the interior. During annealing, the in-situ reaction of trapped-in species likely yields gaseous products (e.g., CO, CH4, H2O) that diffuse out of the particles, leaving sufficient Ti and O to enable crystallization of anatase-TiO2.Preliminarily, enhanced photocatalytic activity is found for the novel TiO2 nanostructures for hydrogen production from water reduction with methanol as a sacrificial agent. Decreased band-gap energy and increased absorbance in both the high-energy (i.e., 200 nm – 250 nm) and low-energy (i.e., 340 nm – 440 nm) UV regions are measured compared to that of commercial anatase.

Photocatalytic Hydrolysis-A Sustainable Option for the Chemical Upcycling of Polylactic Acid.

Plastic waste is a critical global issue, yet current strategies to avoid committing plastic waste to landfills include incineration, gasification, or pyrolysis high carbon emitting and energy consuming approaches. However, plastic waste can become a resource instead of a problem if high value products, such as fine chemicals and liquid fuel molecules, can be liberated from controlled its decomposition. This letter presents proof of concept on a low-cost, low energy approach to controlled decomposition of plastic, photocatalytic hydrolysis. This approach integrates photolysis and hydrolysis, both slow natural decomposition processes, with a photocatalytic process. The photocatalyst, α-Fe2O3, is embedded into a polylactic acid (PLA) plastic matrix. The photocatalyst/plastic composite is then immersed in water and subjected to low-energy (25 W) UV light for 90 h. The monomer lactide is produced as the major product. α-Fe2O3 (6.9 wt %) was found to accelerate the PLA degradation pathway, achieving 32% solid transformation into liquid phase products, in comparison to PLA on its own, which was found to not decompose, using the same conditions. This highlights a low energy route toward plastic waste upgrade and valorization that is less carbon intensive than pyrolysis and faster than natural degradation. By directly comparing a 25 W (0.025 kWh) UV bulb with a 13 kWh furnace, the photocatalytic reaction would directly consume 520× less energy than a conventional thermochemical pathway. Furthermore, this technology can be extended and applied to other plastics, and other photocatalysts can be used.

An ab initio insight into the structural, physical, thermodynamic and optoelectronic properties of superconducting Heusler-like LiGa2Rh

Heusler alloys have drawn attention in material science because some of them show ferromagnetism without a classical magnetic element within the structure and a few of them show superconductivity. In our study, we observe the structural, mechanical, thermodynamic, electronic and optical properties of LiGa2Rh Heusler superconductor in a cubic system using DFT based first-principles calculation. The structure is found to be very ductile with high anisotropy nature and band structure suggests its metallicity. According to optical properties, the maximum amount of absorption occurs for low energy UV photons, with plasma frequency occurring at 16.309 eV. In the UV region, the amount of reflectivity and optical conductivity also high but the refractive index has a broad peak in the visible region. We found here a negative magnetic moment which is -0.98µB. Our analysis shows that this structure has a huge probability in optoelectronic applications.

Water Clusters in Interaction with Corannulene in a Rare Gas Matrix: Structures, Stability and IR Spectra

The interaction of polycyclic aromatic hydrocarbons (PAHs) with water is of paramount importance in atmospheric and astrophysical contexts. We report here a combined theoretical and experimental study of corannulene-water interactions in low temperature matrices and of the matrix’s influence on the photoreactivity of corannulene with water. The theoretical study was performed using a mixed density functional based tight binding/force field approach to describe the corannulene-water clusters trapped in an argon matrix, together with Born-Oppenheimer molecular dynamics to determine finite-temperature IR spectra. The results are discussed in the light of experimental matrix isolation FTIR spectroscopic data. We show that in the solid phase, π isomers of (C20H10)(H2O)n, with n = 2 or 3, are energetically favored. These π complexes are characterized by small shifts in corannulene vibrational modes and large shifts in water bands. These π structures, particularly stable in the case of the water trimer where the water cluster is trapped “inside” the corannulene bowl, may account for the difference in photoreactivity of non-planar–compared to planar–PAHs with water. Indeed, planar PAHs such as pyrene and coronene embedded in H2O:Ar matrices form σ isomers and react with water to form alcohols and quinones under low energy UV irradiation, whereas no photoreactivity was observed for corannulene under the same experimental conditions.

Molecular Solar Thermal Systems towards Phase Change and Visible Light Photon Energy Storage.

Molecular solar thermal (MOST) systems have attracted tremendous attention for solar energy conversion and storage, which can generate high-energy metastable isomers upon capturing photon energy, and release the stored energy as heat on demand during back conversion. However, the pristine molecular photoswitches are limited by low storage energy density and UV light photon energy storage. Recently, numerous pioneering works have been focused on the development of MOST systems towards phase change (PC) and visible light photon energy storage to increase their properties. On the one hand, the strategy of simultaneously capturing isomerization enthalpy and PC energy between solid and liquid can not only offer high latent heat, but also promote the development of sustainable energy systems. On the other hand, the efficient photon energy storage in the visible light range opens a tremendously fascinating avenue to fabricate MOST systems powered under natural sunlight. Here, the recent advances of MOST systems towards PC and visible light photon energy storage are systematically summarized, the most promising advantages and current challenges are analyzed, and emerging strategies and future research directions are proposed.

Electron Holes in G-Quadruplexes: The Role of Adenine Ending Groups.

The study deals with four-stranded DNA structures (G-Quadruplexes), known to undergo ionization upon direct absorption of low-energy UV photons. Combining quantum chemistry calculations and time-resolved absorption spectroscopy with 266 nm excitation, it focuses on the electron holes generated in tetramolecular systems with adenine groups at the ends. Our computations show that the electron hole is placed in a single guanine site, whose location depends on the position of the adenines at the 3′ or 5′ ends. This position also affects significantly the electronic absorption spectrum of (G+)● radical cations. Their decay is highly anisotropic, composed of a fast process (<2 µs), followed by a slower one occurring in ~20 µs. On the one hand, they undergo deprotonation to (G-H2)● radicals and, on the other, they give rise to a reaction product absorbing in the 300–500 nm spectral domain.

UV–annealing synthesis of sulfur-doped graphene for bisphenol A electrocatalytic degradation

Introducing sulfur atoms into the graphene structure is effective in improving the properties of graphene materials. Considering that the traditional annealing process consumes high energy for high-content sulfur doping, a simple and low-energy UV–annealing method is proposed to prepare sulfur-doped graphene. As a result, the sulfur-doped graphene synthesized using this method had higher sulfur content, larger defect degree, and excellent electrocatalytic degradation performance than materials obtained from the annealing method. Under optimum conditions, the degradation efficiency of bisphenol A (BPA) could reach 100% within 40 min. Results showed that 1O2, O2·−, and active chlorine played major roles in the electrocatalytic degradation of BPA. S atoms were doped at the edge of graphene by using the UV–annealing method, whereas S atoms were doped at the skeleton of graphene by using the traditional annealing process. In addition, the possible degradation pathways of BPA were proposed. Therefore, this study provides a new strategy for the practical application of sulfur-doped graphene by using the UV–annealing method in the future.

Guanine Radicals Generated in Telomeric G-Quadruplexes by Direct Absorption of Low-Energy UV Photons: Effect of Potassium Ions.

The study deals with the primary species, ejected electrons, and guanine radicals, leading to oxidative damage, that is generated in four-stranded DNA structures (guanine quadruplexes) following photo-ionization by low-energy UV radiation. Performed by nanosecond transient absorption spectroscopy with 266 nm excitation, it focusses on quadruplexes formed by folding of GGG(TTAGGG)3 single strands in the presence of K+ ions, TEL21/K+. The quantum yield for one-photon ionization (9.4 × 10−3) was found to be twice as high as that reported previously for TEL21/Na+. The overall population of guanine radicals decayed faster, their half times being, respectively, 1.4 and 6.7 ms. Deprotonation of radical cations extended over four orders of magnitude of time; the faster step, concerning 40% of their population, was completed within 500 ns. A reaction intermediate, issued from radicals, whose absorption spectrum peaked around 390 nm, was detected.

A Study on a 355nm UV-pulsed Laser Processing of Polypropylene Filled with Copper Micro-particles

This study investigated 355nm UV-pulsed laser processing of a 150 thick film of polypropylene filled with copper particles. Generally, processing polypropylene with a low beam energy UV laser is difficult because the material’s absorption rate is less than 1% in UV wavelengths. However, polypropylene filled with copper particles is easily processed by UV laser, because copper has a UV absorption rate of more than 70%. The absorbed heat of the copper is transmitted to the polypropylene, accomplishing the machining process. Experimental results were observed while changing the laser processing speed rate. Also, the mechanism of the experimental results was investigated theoretically and experimentally

Photo-activated self-healing bio-based polyurethanes

A series of self-healing bio-based polyurethanes (SHPU) was synthesized by embedding coumarin derivatives into bio-based polyurethanes. The self-healing process of SHPU was activated by low energy UV light. UV–vis spectroscopy exhibited disappearance of a band at 340 nm. This band is corresponding to the photo-cycloaddition of 6,7-dihydroxycoumarin, which was six times faster than esculin upon irradiation. Higher dimerization rate of 6,7-dihydroxycoumarin (0.006 min−1) enhanced the healing efficiency of PU compared to esculin at 0.0009 min−1. FTIR spectroscopy analysis showed photodegradation of irradiated PUE with lower intensity of CO and CC peaks at 1707 cm−1 and 1530 cm−1 corresponding to breaking of urethane bond. Furthermore, cut wound in 6,7-dihydroxycoumarin in polyurethane (PUC) was positively healed compared to esculin embedded in polyurethane (PUE) as observed in the optical micrographs. SEM micrograph analysis provided further insight of the high efficiency of PUC in repairing the cut wound compared to PUE. Moreover, PUE experienced a large decrease in electrical conductivity compared to PUE due to its incapability in absorbing more photons that induced PUE encountered chain scissoring. This hindered the lithium ion hopping in PUE.

Photoluminescence Properties in Aliphatic-Aromatic Biodegradable Polymers Induced by Low Energy Radiation

AbstractPristine poly(butylene adipate-co-terephthalate) (PBAT) is a biodegradable aliphatic-aromatic copolyester that shows no photoluminescent features. The radio induction of photoluminescence (PL) properties in PBAT, after exposure to high doses of gamma radiation, was firstly reported in 2014. These new PL properties have great potential for applications at “in vitro” imaging of human cancer, bio-imaging devices and radiation dosimetry. In this paper, we report the radio induction of photoluminescence (PL) properties in PBAT, after exposure to low energy UV irradiation. In this investigation, films of PBAT, produced by the wire-bar coating technique, were exposed to UV radiation for periods of time ranging from 50 to 500 hours. The PL emission analysis revealed that UV irradiation performed under O2 rich air atmosphere enhances the PL output when compared to irradiations performed in the air. FTIR data confirm that the mechanism behind the UV photo-induction of PL features are similar to the mechanism suggested for gamma radio-induction PL emission. The PL intensity x Spectral Irradiance relationship and RGB color components, the green (G) and blue (B) components, can be used to perform 2D UV dosimetry. The high quantum yield emission of UV-induced PL near 500 nm observed in PBAT is a very interesting finding because it involves the development of a new cheap biodegradable photoluminescent polymer that finds application in drug delivery, bio-imaging devices and also in 2D dosimetry.

Blue-Emissive Cobalt(III) Complexes and Their Use in the Photocatalytic Trifluoromethylation of Polycyclic Aromatic Hydrocarbons.

Room-temperature luminescent CoIII complexes (1 and 2) are presented that exhibit intense ligand-to-metal and ligand-to-ligand charge transfer absorption in the low-energy UV region (λabs ≈360-400 nm) and low-negative quasi-reversible reduction events (E1/2(red) =-0.58 V and -0.39 V vs. SCE for 1 and 2, respectively). The blue emission of 1 and 2 at RT is due to the large bite angles and strong σ-donation of the ligands, the combined effect of which helps to separate the emissive 3 LMCT (triplet ligand-to-metal charge transfer) and the non-emissive 3 MC (triplet metal-centered) states. 1 and 2 were found to be powerful photo-oxidants (ECoIII*/CoII =2.26 V and 2.75 V vs. SCE of 1 and 2, respectively) and were used as inexpensive photoredox catalysts for the regioselective mono(trifluoromethylation) of polycyclic aromatic hydrocarbons (PAHs) in good yields (ca. 40-58 %).

Wavelength-Selective Coupling and Decoupling of Polymer Chains via Reversible [2 + 2] Photocycloaddition of Styrylpyrene for Construction of Cytocompatible Photodynamic Hydrogels.

Reversible photocycloaddition reactions have previously been employed in chemical cross-linking for the preparation of biomaterial scaffolds. However, the processes require activation by high-energy UV light, rendering them unsuitable for modification in biological environments. Here we demonstrate that the [2 + 2] photocycloaddition of styrylpyrene can be activated by visible light at λ = 400-500 nm, enabling rapid and effective conjugation and cross-linking of poly(ethylene glycol) (PEG) in water and under mild irradiation conditions (I = 20 mW cm-2). Notably, the reversion of the cycloaddition can be triggered by low-energy UV light at λ = 340 nm, which allows for efficient cleavage of the dimer adduct. Using this wavelength-gated reversible photochemical reaction we are able to prepare PEG hydrogels and modulate their mechanical properties in a bidirectional manner. We also demonstrate healing of the fractured hydrogel by external light triggers. Furthermore, we show that human mesenchymal stem cells can be encapsulated within the gels with high viability post encapsulation. This photochemical approach is therefore anticipated to be highly useful in studies of cell mechanotransduction, with relevance to disease progression and tissue regeneration.

Three zinc iodide complexes based on phosphane ligands: syntheses, structures, optical properties and TD-DFT calculations.

Three zinc iodide complexes based on phosphane ligands, namely diiodidobis(triphenylphosphane-κP)zinc(II), [ZnI2(C18H15P2)2], (1), diiodidobis[tris(4-methylphenyl)phosphane-κP]zinc(II), [ZnI2(C21H21P2)2], (2), and [bis(diphenylphosphoryl)methane-κ2O,O']zinc(II) tetraiodidozinc(II), [Zn(C25H22O2P2)3][ZnI4], (3), have been synthesized and characterized. Single-crystal X-ray diffraction revealed that the structures of (1) and (2) are both mononuclear four-coordinated ZnI2 complexes containing two monodentate phosphane ligands, respectively. Surprisingly, (2) spontaneously forms an acentric structure, suggesting it might be a potential second-order NLO material. The crystal structure of complex (3) is composed of two parts, namely a [Zn(dppmO2)3]2+ cation [dppmO2 is bis(diphenylphosphoryl)methane] and a [ZnI4]2- anion. The UV-Vis absorption spectra, thermal stabilities and photoluminescence spectra of the title complexes have also been studied. Time-dependent density functional theory (TD-DFT) calculations reveal that the low-energy UV absorption and the corresponding light emission both result from halide-ligand charge-transfer (XLCT) excited states.

Radicals generated in alternating guanine-cytosine duplexes by direct absorption of low-energy UV radiation.

Recent studies have evidenced that oxidatively damaged DNA, which potentially leads to carcinogenic mutations and aging, may result from the direct absorption of low-energy photons (>250 nm). Herein, the primary species, i.e., ejected electrons and base radicals associated with such damage in duplexes with an alternating guanine-cytosine sequence are quantified by nanosecond transient absorption spectroscopy. The one-photon ionization quantum yield at 266 nm is 1.2 × 10-3, which is similar to those reported previously for adenine-thymine duplexes. This means that the simple presence of guanine, the nucleobase with the lowest ionization potential, does not affect photo-ionization. The transient species detected after 3 μs are identified as deprotonated guanine radicals, which decay with a half-time of 2.5 ms. Spectral assignment is made with the help of quantum chemistry calculations (TD-DFT), which for the first time, provide reference absorption spectra for guanine radicals in duplexes. In addition, our computed spectra predict the changes in transient absorption expected for hole localization as well as deprotonation (to cytosine and bulk water) and hydration of the radical cation.

Adenine radicals generated in alternating AT duplexes by direct absorption of low-energy UV radiation.

There is increasing evidence that the direct absorption of photons with energies that are lower than the ionization potential of nucleobases may result in oxidative damage to DNA. The present work, which combines nanosecond transient absorption spectroscopy and quantum mechanical calculations, studies this process in alternating adenine-thymine duplexes (AT)n. We show that the one-photon ionization quantum yield of (AT)10 at 266 nm (4.66 eV) is (1.5 ± 0.3) × 10-3. According to our PCM/TD-DFT calculations carried out on model duplexes composed of two base pairs, (AT)1 and (TA)1, simultaneous base pairing and stacking does not induce important changes in the absorption spectra of the adenine radical cation and deprotonated radical. The adenine radicals, thus identified in the time-resolved spectra, disappear with a lifetime of 2.5 ms, giving rise to a reaction product that absorbs at 350 nm. In parallel, the fingerprint of reaction intermediates other than radicals, formed directly from singlet excited states and assigned to AT/TA dimers, is detected at shorter wavelengths. PCM/TD-DFT calculations are carried out to map the pathways leading to such species and to characterize their absorption spectra; we find that, in addition to the path leading to the well-known TA* photoproduct, an AT photo-dimerization path may be operative in duplexes.

Organic degradation potential of a TiO2/H2O2/UV–vis system for dental applications

ObjectivesThe combination of TiO2 and H2O2 under light activation constitutes a promising method for disinfection of dental prosthetics and implants, due to production of reactive oxygen species (ROS). The aim of this work was to investigate the organic degradation ability of TiO2 particles in combination with H2O2 and under light activation utilizing the organic dye rhodamine B (RhB). MethodsFive different types of TiO2 particles, consisting of anatase, rutile, or a mixture of these crystalline phases, were combined with H2O2 and RhB, and subsequently exposed to UV (365nm) or visible (405nm) light at an irradiance of 2.1mW/cm2. ResultsIt was found that rutile in combination with low concentrations of H2O2 (1.0–3.5mM) resulted in a degradation of RhB of 96% and 77% after 10min exposure to 365nm and 405nm light, respectively, which was the highest degradation of all test groups. Control measurements performed without light irradiation or irradiation at 470nm, or without TiO2 particles resulted in little or no degradation of RhB. ConclusionsLow H2O2 concentrations (1.0mM–3.5mM) and visible light (405nm) used in combination with rutile TiO2 particles showed the highest RhB degradation capacity. Clinical significanceA combination of TiO2 particles and H2O2 exposed to low energy UV or high energy visible light has an organic degradation capability that could be utilized in applications to kill or inactivate bacteria on medical devices such as dental implants for treatment against, e.g., peri-implantitis.

Absorption of Low-Energy UV Radiation by Human Telomere G-Quadruplexes Generates Long-Lived Guanine Radical Cations.

Telomeres, which are involved in cell division, carcinogenesis, and aging and constitute important therapeutic targets, are prone to oxidative damage. This propensity has been correlated with the presence of guanine-rich sequences, capable of forming four-stranded DNA structures (G-quadruplexes). Here, we present the first study on oxidative damage of human telomere G-quadruplexes without mediation of external molecules. Our investigation has been performed for G-quadruplexes formed by folding of GGG(TTAGGG)3 single strands in buffered solutions containing Na+ cations (TEL21/Na+). Associating nanosecond time-resolved spectroscopy and quantum mechanical calculations (TD-DFT), it focuses on the primary species, ejected electrons and guanine radicals, generated upon absorption of UV radiation directly by TEL21/Na+. We show that, at 266 nm, corresponding to an energy significantly lower than the guanine ionization potential, the one-photon ionization quantum yield is 4.5 × 10-3. This value is comparable to that of cyclobutane thymine dimers (the major UV-induced lesions) in genomic DNA; the quantum yield of these dimers in TEL21/Na+ is found to be (1.1 ± 0.1) × 10-3. The fate of guanine radicals, generated in equivalent concentration with that of ejected electrons, is followed over 5 orders of magnitude of time. Such a quantitative approach reveals that an important part of radical cation population survives up to a few milliseconds, whereas radical cations produced by chemical oxidants in various DNA systems are known to deprotonate, at most, within a few microseconds. Under the same experimental conditions, neither one-photon ionization nor long-lived radical cations are detected for the telomere repeat TTAGGG in single-stranded configuration, showing that secondary structure plays a key role in these processes. Finally, two types of deprotonated radicals are identified: on the one hand, (G-H2)• radicals, stable at early times, and on the other hand, (G-H1)• radicals, appearing within a few milliseconds and decaying with a time constant of ∼50 ms.