UV Photostability Research Articles

Simultaneous enhancements of UV-shielding properties and photostability of polyvinyl butyral by incorporation of MWCNTs

Polymer nanocomposites with proper reinforcement can simultaneously enhance both the UV-shielding and optical properties. Such composite materials are being investigated for many commercial applications, including automotive, window screens etc. However, the inherent challenge is maintaining transparency while using reinforcement to get better optical properties and UV resistance. In this study, Multiwall Carbon Nanotubes (MWCNTs) were reinforced for a range of content (0.5, 1.0, 1.5 and 2.0 wt%) in Polyvinyl Butyral (PVB) matrix to synthesize nanocomposite films for UV-shielding purposes. UV-shielding properties are enhanced as compared to PVB for all compositions. We were adding 0.5 wt% MWCNTs to PVB effectively improved UV wavelength blocking and slightly decreased visible light transparency. UV studies were performed in the 190–1100 nm wavelength range and the values of the absorption edge, direct and indirect bandgap energies and Urbach energy were evaluated. When 0.5 wt% MWCNTs were reinforced into the PVB, the direct and indirect bandgaps changed significantly from 4.50 to 4.91 eV–3.01 eV and 4.06 eV respectively, while the Urbach energy increased from 0.73 eV to 1.16 eV. These results show that the UV shielding and photostability of PVB nanocomposite films are significantly changed with the low dispersion of MWCNTs.

Constraints on the emergence of RNA through non-templated primer extension with mixtures of potentially prebiotic nucleotides.

The emergence of RNA on the early Earth is likely to have been influenced by chemical and physical processes that acted to filter out various alternative nucleic acids. For example, UV photostability is thought to have favored the survival of the canonical nucleotides. In a recent proposal for the prebiotic synthesis of the building blocks of RNA, ribonucleotides share a common pathway with arabino- and threo-nucleotides. We have therefore investigated non-templated primer extension with 2-aminoimidazole-activated forms of these alternative nucleotides to see if the synthesis of the first oligonucleotides might have been biased in favor of RNA. We show that non-templated primer extension occurs predominantly through 5'-5' imidazolium-bridged dinucleotides, echoing the mechanism of template-directed primer extension. Ribo- and arabino-nucleotides exhibited comparable rates and yields of non-templated primer extension, whereas threo-nucleotides showed lower reactivity. Competition experiments confirmed the bias against the incorporation of threo-nucleotides. The incorporation of an arabino-nucleotide at the end of the primer acts as a chain terminator and blocks subsequent extension. These biases, coupled with potentially selective prebiotic synthesis, and the templated copying that is known to favour the incorporation of ribonucleotides, provide a plausible model for the effective exclusion of arabino- and threo-nucleotides from primordial oligonucleotides.

Enhancing Ultraviolet Stability and Performance of Wide Bandgap Perovskite Solar Cells Through Ultraviolet Light-Absorbing Passivator.

Ultraviolet light (UV) has caused tremendous damage to perovskite solar cells (PSCs), degrading the perovskite and shortening their lifetime. Defects act as non-radiative recombination sites, accelerate the degradation process, reduce the efficiency of the device and weaken the stability of solar cell. In this work, to realize efficient and stable p-i-n wide bandgap solar cells under UV, a synergetic strategy utilizing UV light-absorbing passivator, (Trifluoroacetyl) benzotriazole (TFABI), enhance UV photostability and regulate the defect passivation is proposed. By using TFABI, the degradation of the perovskite absorption layer under UV light is suppressed, spectral response is enhanced and the Pb vacancy defects are passivated. As a result, the target device achieves an efficiency of 21.54%, exhibiting excellent long-term stability under 365nm UV irradiation. After 60 h of irradiation, it retains 85% of its initial value (60mWcm-2 , RH 25-30%, 25°C).

Recent developments in sunscreens based on chromophore compounds and nanoparticles.

Sunscreen formulations have undergone significant advancements in recent years, with a focus on improving UV radiation protection, photostability, and environmental sustainability. Chromophore compounds and nanoparticles have emerged as key components in these developments. This review highlights the latest research and innovations in chromophore compounds and nanoparticle-based sunscreens. It discusses the role of nanoparticles, such as zinc oxide and titanium dioxide, in scattering and absorbing UV radiation while remaining cosmetically acceptable. Chromophore compounds, encapsulated in nanoparticles, are explored for their potential to enhance UV protection by absorbing specific wavelengths of light. Additionally, advances in photo-stability, broad-spectrum protection, antioxidant inclusion, and biodegradability are discussed. The evolving landscape of sunscreen technology aims to provide more effective and environment-friendly solutions for safeguarding skin from the sun's harmful effects.

Saponin-based natural nanoemulsions as alpha-tocopherol delivery systems for dermal applications

Nanoemulsions can be produced using simple methods and compounds from natural sources. They can increase water dispersibility and bioavailability and optimise active ingredient dispersion in particular skin layers. Lipophilic compounds of the vitamin E family (tocopherols and tocotrienols) are well-known for their high antioxidant activity and capacity to protect the skin from oxidative stress. In this context, oil-in-water (o/w) nanoemulsions with and without α-tocopherol (Vitamin E, VE) were formulated with two emulsifier alternatives, Quillaja saponin (QS), and a combination of QS with Tribulus terrestris (QSTT) (50/50, w/w). The emulsions were evaluated concerning stability, microstructure, droplet size, colour attributes, encapsulation efficiency, UV photostability, antioxidant activity, and in vitro permeation studies to assess the delivery potential. Results showed highly stable systems, with round-shape droplets of 80–121 nm size. QS and QSTT samples' colours were close to white and light brownish, respectively. The topical nano cream had the capacity to entrap VE, producing a protective effect from UV degradation, and very significant antioxidant activity, with IC50 values around 0.01 %wt. The skin permeation profiles showed the efficiency of the formulations in the delivery of VE, with permeabilities between 64 and 74 µg/cm2, while the control sample showed no VE permeation.

Polydopamine-coated lignin nanoparticles in polysaccharide-based films: A plasticizer, mechanical property enhancer, anti-ultraviolet agent and bioactive agent

The potential of polysaccharide film as an alternative to petroleum-based plastics is being closely watched. To solve the defects of poor water resistance, poor flexibility and no bioactivity of polysaccharide-based films, polydopamine-coated lignin nanoparticles (LNP@PDA) were prepared and loaded on polysaccharide matrix to obtain composite films. LNP@PDA has good biocompatibility and can be dispersed homogeneously in polysaccharide matrix. The tight entanglement and hydrogen bonding between LNP@PDA and pectin promoted the formation of dense structure in film, and allowed the films to exhibit a nano-scale rough surface (7.61–20.90 nm). Composite films have higher mechanical strength (35.76 MPa) and water contact angle (92.42°), and exhibit unique antioxidant and antibacterial activities. Even without the addition of any plasticizers, the composite film exhibits attractive flexibility that is not present in polysaccharide-based films. When LNP@PDA loading exceeded 5%, composite films almost completely blocked the UVA (400-320 nm), UVB (320-275 nm) and UVC (275-200 nm) spectra and remained so after 24 h of UV irradiation, which demonstrated their excellent UV resistance and photostability. Furthermore, the universality results verify that LNP@PDA is also suitable for other different polysaccharide-based (such as starch, sodium alginate, agar, carrageenan, carob gum) films. Interestingly, the shear-thinning property of the film-forming fluid allows it to be sprayed through a sprayer bottle onto the surface of fruit or food packaging. These results suggest that LNP@PDA can be loaded into polysaccharide-based films as plasticizers, mechanical property enhancers, anti-UV agents, antioxidants and antimicrobial agents. This provides a brand-new strategy for producing high-performance polysaccharide-based food active packaging/coating.

Photostability of vitamin C in industrialized fruit juices and isomers determination by HPLC-DAD

L-ascorbic acid (LAA) and D-isoascorbic acid (DIAA) are two of the most important antioxidants in industrialized fruit products as mixed fruit juices, fruit concentrates, and jams, in which they are added as antioxidants and as a nutrient. Despite that, LAA may undergo oxidative- and photo-degradation during storage, compromising its concentration and activities in these food products. In this work we aimed to optimize a method for the identification and quantification of LAA and DIAA by high performance liquid chromatography with diode-array detection (HPLC-DAD) using a NH2 column and a pre-heated mobile phase. A further aim was to investigate if food packing actually protects fruit juices against LAA photodegradation. For the UV photostability test, samples were UV-irradiated at 1416 μW cm−2, at 28 ± °C, and with a radiation energy above 200 W h m−2. The optimized HPLC method provided complete peak resolution of vitamin C isomers in less than nine min run-time. At the end of photostability tests with fruit juices and jellies packaged in polyethylene terephthalate and glass bottles or flasks, L-ascorbic acid was undetectable, suggesting that the packages did not provide effective protection against vitamin C photodegradation. To the best of our knowledge, vitamin C photostability in fruit products was previously unreported.

Development of glow-in-the-dark and color-tunable poly(methyl methacrylate) plastic concrete immobilized with rare-earth aluminate

A simple method is reported for the prospective industrial production of lightweight poly(methyl methacrylate) (PMMA) plastic concrete with persistent afterglow. Nanoparticles (NPs) of lanthanide activated aluminate (LAA) pigment were molded into a plastic bar. With the uniform dispersion of LAA NPs in the plastic fluid, the produced plastic bar can be made transparent. was A simple polymerization of methyl methacrylate (MMA; bulk material) blended with silica nanoparticles (filler), and LAA nanoparticles (luminous agent) was applied in the presence of 2,2-azobisisobutyronitrile (AIBN) catalyst to provide photoluminescent PMMA plastic concrete. In studies, LAA NPs were found to have sizes between 9 and 95 nm. When excited at 369 nm, the luminescent PMMA concrete displayed an emission peak at 518 nm. For pigment concentrations over 1%, persistent photoluminescence was observed, whereas fluorescence was tracked for the LAA contents equal to or below 1%. The manufactured plastic concrete was shown to exhibit photochromism from colorless under daytime light to green below UV, and greenish-yellow in the dark. By measuring the static contact angle, we were able to confirm the excellent superhydrophobic activity. Indications of enhanced UV protection and photostability were monitored upon increasing LAA ratio in the concrete bulk. Strong durability, reversibility and continuous afterglow emission were hallmarks of the photoluminescent hard composite concrete. The created plastic concrete morphology, elemental content and hardness properties were studied.

Photochemoprevention of topical formulation containing purified fraction of Inga edulis leaves extract.

Natural antioxidants have attracted attention for their therapeutic use as photochemopreventive agents. Inga edulis leaves extract and its purified fraction have high polyphenolic content and high antioxidant capacity. In addition, they presented UV photostability and low citotoxicity in fibroblast cells. In this context, this study first aimed at development of topical formulation containing purified fraction of I. edulis extract and the evaluation of skin penetration of the compounds. Moreover, the photoprotective/photochemopreventive potential of the formulation containing I. edulis purified fraction were investigated in vitro and in vivo. The topical formulation containing 1% of the purified fraction of I. edulis increased the endogenous antioxidant potential of the skin, and vicenin-2 and myricetin compounds were able to penetrate the epidermis and dermis. Additionally, the purified fraction (25 and 50 mg/mL) showed a photoprotective effect against UVA and UVB radiation in L929 fibroblast cells. In vivo studies have shown that the formulation added with purified fraction provided an anti-inflammatory effect on the skin of animals after UVB exposure, since it was observed a reduction in MPO activity, IL-1β and TNF-α cytokines, and CXCL1/KC chemokine concentrations. In conclusion, the purified fraction of I. edulis, rich in phenolic compounds, when incorporated in topical formulation, appears as an alternative to prevent skin damages induced by UV radiation, due to its antioxidant and anti-inflammatory properties.

A Bioinspired Skin UV Filter with Broadband UV Protection, Photostability, and Resistance to Oxidative Damage.

In recent years, sunscreens' adverse impacts on the environment and biology have gained wide attention. The improvement of sunscreen safety has become one of the major priorities in skin photoprotection research. It is an effective strategy to develop bionic photoprotective materials by simulating the photoprotective mechanism existing in nature. Inspired by the photoprotective mechanisms of skin and plant leaves, the bionic photoprotective material CS-SA-PDA nanosheet was developed using the free radical grafting method and Michael addition, with natural melanin analogue polydopamine (PDA) nanoparticles and plant sunscreen molecular sinapic acid (SA) as sun protection factors and natural polymer chitosan (CS) as the connecting arm. The results show that CS-SA-PDA can effectively shield UVB and UVA due to the possible synergistic effect between PDA and SA. The introduction of polymer CS significantly improved the photostability of SA and reduced the skin permeability of PDA nanoparticles. The CS-SA-PDA nanosheet can also effectively scavenge photoinduced free radicals. Furthermore, in vivo toxicity and anti-UV evaluations confirm that CS-SA-PDA has no skin irritation and is excellent against skin photodamage, which makes it an ideal skin photoprotective material.

Preparation of transparent photoluminescence plastic concrete integrated with lanthanide aluminate

A simple strategy was presented for potential industrial preparation of persistent afterglow lightweight plastic concrete toward smart hard surfaces. Rare-earth activated aluminate (REA) pigment nanoparticles (NPs) were integrated into plastic bar. The transparency of the prepared plastic bar can be achieved by consistent distribution of REA NPs in the plastic fluid. Unsaturated polyester resin (bulk material) was mixed with silica nanoparticles (filler) and REA NPs (luminescent agent) using methyl ethyl ketone peroxide as hardener. The curing process was accomplished for a few minutes at room temperature. The diameters of REA NPs were reported in the range of 6–11 nm. The phosphor-concrete composite can be industrially applied onto a variety of hard surfaces. The photoluminescent plastic concrete showed an emission band at 515 nm upon excitation at 372 nm. Persistent photoluminescence was detected for pigment concentrations higher than 1%, whereas fluorescence emission was monitored for pigment concentrations equal to 1%. Photochromism was observed for the prepared plastic concrete as different colors were detected under different light conditions, including colorless under daytime light, green underneath UV rays, and greenish-yellow under darkness as proved by luminescence spectra and CIE Lab parameters. The static contact angle measurements proved good superhydrophobic activity. An improved UV protection and photostability were detected. The photoluminescent hard composite concrete displayed highly durability and reversible persistent afterglow emission. The morphology, elemental composition and hardness features of the prepared plastic concrete were investigated.

Reversible stimuli responsive lanthanide-polyoxometalate-based luminescent hydrogel with shape memory and self-healing properties for advanced information security storage

The development of information security storage materials with high-level of security and low-cost is still a challenging task. Herein, a lanthanide-polyoxometalate-based luminescent hydrogel was constructed by noncovalent cross-linked gelatin/Na9EuW10O36 network and covalent cross-linked polyacrylamide network. The acquired hydrogel exhibited unique reversible luminescent switching properties under the stimulation of HCl/NH3 and Fe3+/ethylenediamine tetraacetic acid disodium salt, respectively. It is well suitable for reversible writing and erasing of information, as well as protecting information. Encouragingly, the hydrogel also possessed good temperature-induced shape memory and self-healing properties for fabricating two- or three-dimensional information platform. As a result, the dual-stimuli luminescence response, shape memory, and self-healing characteristics were combined to improve the security of information effectively by way of the optimized design of encryption/decryption strategies. Furthermore, the hydrogel possessed relatively good UV photostability and low toxicity. To our knowledge, lanthanide-polyoxometalate-based luminescent hydrogel with dual-stimuli luminescence response, shape memory, and self-healing properties simultaneously for information security storage, has not yet been reported. This work provides an alternative strategy for constructing the lanthanide-polyoxometalate-based luminescent hydrogel for advanced information security storage.

610 Development of a natural product-based sunscreen

Sunscreens are a cornerstone of skin cancer prevention; however, currently available sunscreens have limitations. Concerns regarding current organic sunscreen agents include photodegradation, potential disruption of endocrine pathways, and paradoxical generation of damaging reactive oxygen species (ROS). Recent studies by the FDA have shown that organic sunscreens permeate into systemic circulation at levels warranting further safety testing, highlighting the importance of investigating alternative strategies for safe and effective photoprotection. Towards this goal, we previously conducted high-throughput screening of natural compounds for photoprotective potential, quantifying UV spectral absorbance, photostability, cytotoxicity, and ROS generation. From a pilot set of 915 compounds, we prioritized 11 candidates of interest for confirmatory photostability testing and follow-on in vitro SPF testing at 5wt% in P2 formulation. Top performers were diosmin (DIO; SPF 2.7), isoliquiritigenin (IQL; SPF 2.5), ferulic acid (FA; SPF 3.1), and cytisine (CYT; SPF 6.3). To create a broad-spectrum formulation, these agents were assessed individually and in combination for in vitro SPF and critical wavelength (λcrit), and in vivo in C57BL/6J mice for protection against ultraviolet radiation (UVR)-induced cyclobutane pyrimidine dimer (CPD) formation and irritant contact dermatitis potential. 10% DIO + 10% FA + 5% CYT was the best performer of our test combinations, with a mean in vitro SPF of 48.6 (SD 3.2), λcrit of 373, and 92.4% CPDs blocked (SD 3.5%). Other promising combinations utilizing varying concentrations of FA and CYT with DIO or IQL also demonstrated λcrit>370 and SPF>15, i.e. the FDA minimum requirements for decreasing the risk of skin cancer. None of the combinations induced irritant dermatitis as assessed by gross and histologic examination after 5 repeated applications to shaved dorsal skin every 2 days. Collectively, these data demonstrate proof of concept for high throughput screening as a method of identifying candidate alternative sunscreen agents toward the formulation of a natural product-based sunscreen.

AIE Molecules UV‐Filtering Effect Improves the Photostability of Organic Solar Cells

AbstractDue to the poor stability of organic solar cells (OSCs), especially ultraviolet light (UV) stability, they are not yet up to the standard for commercial applications. Inverted devices based on the ZnO electron transport layer (ETL) are relatively thermal‐ and air‐stable, while their UV light stability is poor. Moreover, the active layer materials undergo severe degradation under UV light, which also causes the degradation of the device. Here, aggregation‐induced emission (AIE) molecules as an optical barrier layer are coated between ZnO‐ETL and active layer to fabricate efficient OSCs with excellent UV photostability. AIE molecules can avoid direct photodegradation of the active layer materials by absorbing UV light. At the same time, they can passivate the oxygen defects on the ZnO surface and prevent photocatalytic degradation of the active layer materials. Therefore, the ZnO/TPIZ‐based devices maintain 84% of the original power conversion efficiency (PCE) with continuous irradiation by 5 mW cm–2 UV light (365 nm) for 1500 h, and similarly T80 for more than 700 h under 20 mW cm–2 UV light exposure. Moreover, the ZnO/TPIZ‐based devices also preserve excellent thermal stability accompanying the upgrading of PCE.

Utilizing the unique charge extraction properties of antimony tin oxide nanoparticles for efficient and stable organic photovoltaics

Simultaneously enhancing device performance and longevity, as well as balancing the requirements on cost, scalability, and simplification of processing, is the goal of interface engineering of organic solar cells (OSCs). In our work, we strategically introduce antimony (Sb 3+ ) cations into an efficient and generic n-type SnO 2 nanoparticles (NPs) host during the scalable flame spray pyrolysis synthesis. Accordingly, a significant switch of conduction property from an n-type character to a p-type character is observed, with a corresponding shift in the work function (WF) from 4.01 ± 0.02 eV for pristine SnO 2 NPs to 5.28 ± 0.02 eV for SnO 2 NPs with 20 mol. % Sb content (ATO). Both pristine SnO 2 and ATO NPs with fine-tuned optoelectronic properties exhibit remarkable charge carrier extraction properties, excellent UV resistance and photo-stability being compatible with various state-of-the-art OSCs systems. The reliable and scalable pristine SnO 2 and ATO NPs processed by doctor-blading in air demand no complex post-treatment. Our work offers a simple but unique approach to accelerate the development of advanced interfacial materials, which could circumvent the major existing interfacial problems in solution-processed OSCs. • Introducing antimony cations to effectively dope the n-type SnO 2 nanoparticles. • In-depth characterization of the cation doping effect and mechanisms. • Validation of the generic applicability of the p-type doped nanoparticles for organic photovoltaic applications. • Demonstrating efficient and stable organic solar cells based on state-of-the-art organic photovoltaic materials.

Free Radicals and ROS Induce Protein Denaturation by UV Photostability Assay.

Oxidative stress, photo-oxidation, and photosensitizers are activated by UV irradiation and are affecting the photo-stability of proteins. Understanding the mechanisms that govern protein photo-stability is essential for its control enabling enhancement or reduction. Currently, two major mechanisms for protein denaturation induced by UV irradiation are available: one generated by the local heating of water molecules bound to the proteins and the other by the formation of reactive free radicals. To discriminate which is the likely or dominant mechanism we have studied the effects of thermal and UV denaturation of aqueous protein solutions with and without DHR-123 as fluorogenic probe using circular dichroism (CD), synchrotron radiation circular dichroism (SRCD), and fluorescence spectroscopies. The results indicated that the mechanism of protein denaturation induced by VUV and far-UV irradiation were mediated by the formation of reactive free radicals (FR) and reactive oxygen species (ROS). The development at Diamond B23 beamline for SRCD of a novel protein UV photo-stability assay based on consecutive repeated CD measurements in the far-UV (180–250 nm) region has been successfully used to assess and characterize the photo-stability of protein formulations and ligand binding interactions, in particular for ligand molecules devoid of significant UV absorption.

In Vitro Evaluation of the Photoprotective Potential of Quinolinic Alkaloids Isolated from the Antarctic Marine Fungus Penicillium echinulatum for Topical Use.

Marine-derived fungi proved to be a rich source of biologically active compounds. The genus Penicillium has been extensively studied regarding their secondary metabolites and biological applications. However, the photoprotective effects of these metabolites remain underexplored. Herein, the photoprotective potential of Penicillium echinulatum, an Antarctic alga-associated fungus, was assessed by UV absorption, photostability study, and protection from UVA-induced ROS generation assay on human immortalized keratinocytes (HaCaT) and reconstructed human skin (RHS). The photosafety was evaluated by the photoreactivity (OECD TG 495) and phototoxicity assays, performed by 3T3 neutral red uptake (3T3 NRU PT, OECD TG 432) and by the RHS model. Through a bio-guided purification approach, four known alkaloids, (-)-cyclopenin (1), dehydrocyclopeptine (2), viridicatin (3), and viridicatol (4), were isolated. Compounds 3 and 4 presented absorption in UVB and UVA-II regions and were considered photostable after UVA irradiation. Despite compounds 3 and 4 showed phototoxic potential in 3T3 NRU PT, no phototoxicity was observed in the RHS model (reduction of cell viability < 30%), which indicates their very low acute photoirritation and high photosafety potential in humans. Viridicatin was considered weakly photoreactive, while viridicatol showed no photoreactivity; both compounds inhibited UVA-induced ROS generation in HaCaT cells, although viridicatol was not able to protect the RHS model against UVA-induced ROS production. Thus, the results highlighted the photoprotective and antioxidant potential of metabolites produced by P. echinulatum which can be considered a new class of molecules for photoprotection, since their photosafety and non-cytotoxicity were predicted using recommended in vitro methods for topical use.

Electroencapsulation of Trans-resveratrol in Nanoparticles Composed of Silk Fibroin and Soluble Eggshell Membrane Protein

The beneficial effects of trans-resveratrol on health are widely accepted. However, when exposed to heat and UV light, the degradation of trans-resveratrol to less active form cis-resveratrol limits its use in industrial applications. Due to this reason, it is crucial to preserve the stability of trans-resveratrol by using carrier systems. This study aimed to encapsulate the trans-resveratrol in core/shell nanoparticles composed of eggshell membrane proteins and silk fibroin, respectively, using a coaxial electrospraying technique to preserve its stability. The size of the nanoparticles ranged from 8.2 to 254 nm. Keeping the encapsulation yield at the maximum level (96.9%), electroencapsulation process parameters which minimize the average particle diameter (23.8 nm) were found to be A (silk fibroin concentration) = 30.7 mg/ml, B (ratio of flow rates) = 0.72, C (applied voltage) = 18.8 kV, and D (distance) = 12.2 cm. Encapsulation efficiency varied between 40.05 and 96.41%. Detection of antioxidant capacity of released trans-resveratrol suggested that nanoparticles could be a suitable delivery system for sustained release of trans-resveratrol with preserved thermal and UV photostability. Central composite design (CCD) and the response surface methodology (RSM) were successfully used to optimize the electroencapsulation process parameters for the preparation of trans-resveratrol loaded core/shell nanoparticles. It was found that these parameters seemed to be varied depending on the response required. Therefore, an optimum process should be investigated to obtain desired responses such as high encapsulation yield, high encapsulation efficiency, and small average particle size while preserving the thermal and UV stabilities at reasonable levels.

Ultrafast excited-state dynamics of promising nucleobase ancestor 2,4,6-triaminopyrimidine.

The ultrafast excited-state dynamics of 2,4,6-triaminopyrimidine - thought to be a promising candidate for a proto-RNA nucleobase - have been investigated via static multireference quantum-chemical calculations and mixed-quantum-classical/trajectory surface-hopping dynamics with a focus on the lowest-lying electronic states of the singlet manifold and with a view towards understanding the UV(C)/UV(B) photostability of the molecule. Ultrafast internal conversion channels have been identified that connect the lowest-lying ππ* electronically-excited state of 2,4,6-triaminopyrimidine with the ground electronic state, and non-radiative decay has been observed to take place on the picosecond timescale via a ππ* out-of-plane NH2 ("oop-NH2") minimum-energy crossing point. The short excited-state lifetime is competitive with the excited-state lifetimes of the canonical pyrimidine nucleobases, affirming the promise of 2,4,6-triaminopyrimidine as an ancestor. Evidence for energy-dependent excited-state dynamics is presented, and the open question of intersystem crossing is discussed speculatively.

Down-conversion Ce-doped TiO2 nanorod arrays and commercial available carbon based perovskite solar cells: Improved performance and UV photostability

Ce-doped TiO2 nanorod arrays as the mesoporous supporting layer and TiO2 compacted electron blocking layer was simultaneously fabricated by one-pot hydrothermal method. Ce-doped TiO2 nanorod was utilized as down-conversion luminescence centers and commercial available carbon was used in hole-transport-free perovskite solar cells. SEM indicated that the doping of Ce reduced the diameter of TiO2 nanorods. XRD and EDS spectra demonstrate the successful incorporation of Ce ions. UV–Vis absorption spectra and PL emission spectra show that the down-conversion center Ce4+ can effectively utilize ultraviolet light and extend the absorption into the ultraviolet region. The carbon-based device using the optimized Ce doping concentration achieved power conversion efficiency (PCE) of 10.1%, which was 24.6% higher than that of undoped device. Ce doping changes the band gap of TiO2 and the Fermi energy level, and thus improve the open circuit voltage. The open circuit voltage decay curve show that Ce-doped TiO2 prolongs electron lifetime. EIS analysis hints that more carriers are generated. The UV stability has also been significantly improved., PCE of the optimized Ce-doped device still retains 90% of the initial value, however, the undoped device decreases to 55% of the initial value under light irradiation at ambient atmosphere for 12 h.