Photochemical Processes Research Articles

The photodissociation dynamics and ultrafast electron diffraction image of cyclobutanone from the surface hopping dynamics simulation

The comprehension of nonadiabatic dynamics in polyatomic systems relies heavily on the simultaneous advancements in theoretical and experimental domains. The gas-phase ultrafast electron diffraction (UED) technique has attracted significant attention as a unique tool for monitoring photochemical and photophysical processes at the all-atomic level with high temporal and spatial resolutions. In this work, we simulate the UED spectra of cyclobutanone using the trajectory surface hopping method at the extended multi-state complete active space second order perturbation theory (XMS-CASPT2) level and thereby predict the results of the upcoming UED experiments in the Stanford Linear Accelerator Laboratory. The simulated results demonstrate that a few pathways, including the C2 and C3 dissociation channels, as well as the ring opening channel, play important roles in the nonadiabatic reactions of cyclobutanone. We demonstrate that the simulated UED signal can be directly interpreted in terms of atomic motions, which provides a unique way of monitoring the evolution of the molecular structure in real time. Our work not only provides numerical data that help to determine the accuracy of the well-known surface hopping dynamics at the high XMS-CASPT2 electronic-structure level but also facilitates the understanding of the microscopic mechanisms of the photoinduced reactions in cyclobutanone.

Investigation of photothermal effects and mechanisms underlying collagen denaturation in laser-assisted skin anastomosis

Based on the thermal damage concept, our work proposes the concept and calculation method of collagen denaturation degree. By integrating experimental calculations with GROMACS molecular dynamics simulation and finite element COMSOL numerical simulation of skin optical properties, we investigate the mechanisms underlying collagen fiber thermal denaturation and photochemical changes induced by laser irradiation. When the energy is below 115.68 J/mm2, the dominant factor in skin wound repair is the thermal energy delivered by the laser. The collagen denaturation degree can be maintained around 0.0199 during an effective laser welding time of 300 s, resulting in a peak temperature of approximately 55℃ and noticeable wrinkling and scattering of monomeric helical protein chains within the fiber structure. This wrinkled structure indicates macroscopic recombination and recoupling of fractured collagen fibers on both sides of the skin wound. However, when the laser energy density further increases to 135.4 J/mm2, there is only a slight increase in collagen denaturation degree without significant alterations observed. For this phenomenon, Finite element simulations based on Helmholtz equation modules reveal that reflectivity towards laser photons decreases significantly across tissue blocks due to enhanced photonics effects. As energy reaches or exceeds 135.4 J/mm2 levels, photothermal effects assume a more prominent role but inevitably lead to higher peak temperatures (70.4℃). Therefore, precise reduction in laser welding time within 300 s can effectively control collagen denaturation within reversible and reasonable ranges.

Photochemical Aerobic Upcycling of Polystyrene Plastics.

Although the introduction of plastics has improved humanity's everyday life, the fast accumulation of plastic waste, including microplastics and nanoplastics, have created numerous problems with recent studies highlighting their involvement in various aspects of our lives. Upcycling of plastics, the conversion of plastic waste to high-added value chemicals, is a way to combat plastic waste that is receiving increased attention. Herein, we describe a novel aerobic photochemical process for the upcycling of real-life polystyrene-based plastics into benzoic acid. A new process employing a thioxanthone-derivative, in combination with N-bromosuccinimide, under ambient air and 390 nm irradiation is capable of upcycling real-life polystyrene-derived products in benzoic acid in yields varying from 24-54%.

Chemical composition, source characteristics, and hygroscopic properties of organic-enriched aerosols in the high Arctic during summer

Arctic regions are extremely sensitive to global warming. Aerosols are one of the most important short-lived climate-forcing agents affecting the Arctic climate. The present study examines the summertime chemical characteristics and potential sources of various organic and inorganic aerosols at a Norwegian Arctic site, Ny-Ålesund (79°N). The results show that organic matter (OM) accounts for 60 % of the total PM10 mass, followed by sulfate (SO42−). Water-soluble organic carbon (WSOC) contributes 62 % of OC. Photochemical processes involving diverse anthropogenic and biogenic precursor compounds are identified as the major sources of WSOC, while water-insoluble organic carbon (WIOC) aerosols are predominantly linked to primary marine emissions. Despite being a remote pristine site, the aerosols show a sign of chemical aging, evidenced by a significant chloride depletion, which was about 82 % on average during the study period. Nitrogen-containing aerosols are likely stemming from migratory seabird colonies and local dust sources around the sampling site. While biogenic, crustal, and sea salt-derived SO42- account for 37%, 8%, and 5% respectively, the remaining 50% is attributed to anthropogenic SO42-. Through chemical tracers, Pearson correlation coefficient matrix, and Hierarchical Cluster Analysis (HCA), the present study identifies soil biota (terrestrial biogenic) and marine emissions, along with their photochemical oxidation processes, as potential sources of Arctic aerosols during summer, while biomass burning and combustion-related sources have a minor contribution. The chemical closure of hygroscopicity highlights that while organics predominantly control aerosol hygroscopicity in the Arctic summer, specific inorganic components like (NH4)2SO4 can significantly increase it on certain days, affecting aerosol-cloud interactions and climate processes over the Arctic during summer. The present study highlights the high abundance of organics and their vital role in the Arctic climate during summer when natural aerosols are conquered.

Synthesis of 3-hydroxybenzoic acid derivatives via photochemical rearrangement of 6-substituted bicyclo[3.1.0]hex-3-en-2-ones

The utilization of a photochemical rearrangement process to transform a wide range of substituted bicyclo[3.1.0]hex-3-en-2-ones into derivatives of 3-hydroxybenzoic acids is reported.

Dearomative Intramolecular meta-Thermocycloadditions of Benzene Rings via Wheland Intermediates.

Dearomative cycloadditions are powerful synthetic transformations utilizing aromatic compounds for cycloaddition reactions. They have been extensively applied to the synthesis of biologically relevant compounds not only because of the complexity generated from simplicity but also the atom- and step-economy. For the most studied yet challenging benzene ring systems, ortho- and para-cycloadditions have been realized both photochemically and thermally, while the meta-cycloadditions are still limited to the photochemical processes tracing back to the 1960s. Herein, we for the first time realized the thermal cycloadditions of benzene rings with alkenes in a meta fashion via Wheland intermediates. A broad spectrum of readily available C(sp2)-rich aniline-tethered enynes were transformed into C(sp3)-rich 3D complex polycyclic architectures simply by stirring in TFA. Moreover, the reaction could be performed in gram-scales and the products could be diversely elaborated.

Dearomative Intramolecular meta‐Thermocycloadditions of Benzene Rings via Wheland Intermediates

Dearomative cycloadditions are powerful synthetic transformations utilizing aromatic compounds for cycloaddition reactions. They have been extensively applied to the synthesis of biologically relevant compounds not only because of the complexity generated from simplicity but also the atom‐ and step‐economy. For the most studied yet challenging benzene ring systems, ortho‐ and para‐cycloadditions have been realized both photochemically and thermally, while the meta‐cycloadditions are still limited to the photochemical processes tracing back to the 1960s. Herein, we for the first time realized the thermal cycloadditions of benzene rings with alkenes in a meta fashion via Wheland intermediates. A broad spectrum of readily available C(sp2)‐rich aniline‐tethered enynes were transformed into C(sp3)‐rich 3D complex polycyclic architectures simply by stirring in TFA. Moreover, the reaction could be performed in gram‐scales and the products could be diversely elaborated.

Recent decline in carbon monoxide levels observed at an urban site in Ahmedabad, India.

Carbon monoxide (CO) is a prominent air pollutant in cities, with far-reaching implications for both local air quality and global atmospheric chemistry. The long-term change in atmospheric CO levels at a specific location is influenced by a complex interplay of local emissions, atmospheric transport, and photochemical processes, making it a subject of considerable interest. This study presents an 8-year analysis (2014-2021) of in situ CO observations using a cutting-edge laser-based analyzer at an urban site in Ahmedabad, western India. The long-term observations reveal a subtle trend in CO levels, masked by contrasting year-to-year variations, particular after 2018, across distinct diurnal time windows. Mid-afternoon (12:00-16:00h) CO levels, reflecting background and regional conditions, remained relatively stable over the study period. In contrast, evening (18:00-21:00h) CO levels, influenced by local emissions, exhibited substantial inter-annual variability without discernible trends from 2014 to 2018. However, post-2018, evening CO levels showed a consistent decline, predating COVID-19 lockdown measures. This decline coincided with the nationwide adoption of Bharat stage IV emission standards and other measures aimed at reducing vehicular emissions. The COVID-19 lockdown in 2020 further resulted in a noteworthy 29% reduction in evening CO levels compared to the pre-lockdown (2014-2019) period, highlighting the potential for substantial CO reduction through stringent vehicular emission controls. The observed long-term changes in CO levels do not align with the decreasing emission estimated by various inventories from 2014 to 2018, suggesting a need for improved emission statistics in Indian urban regions. This study underscores the importance of ongoing continuous CO measurements in urban areas to inform policy efforts aimed at controlling atmospheric pollutants.

Plasmon-Induced Hot Electrons in Nanostructured Materials: Generation, Collection, and Application to Photochemistry.

Plasmon refers to the coherent oscillation of all conduction-band electrons in a nanostructure made of a metal or a heavily doped semiconductor. Upon excitation, the plasmon can decay through different channels, including nonradiative Landau damping for the generation of plasmon-induced energetic carriers, the so-called hot electrons and holes. The energetic carriers can be collected by transferring to a functional material situated next to the plasmonic component in a hybrid configuration to facilitate a range of photochemical processes for energy or chemical conversion. This article centers on the recent advancement in generating and utilizing plasmon-induced hot electrons in a rich variety of hybrid nanostructures. After a brief introduction to the fundamentals of hot-electron generation and decay in plasmonic nanocrystals, we extensively discuss how to collect the hot electrons with various types of functional materials. With a focus on plasmonic nanocrystals made of metals, we also briefly examine those based upon heavily doped semiconductors. Finally, we illustrate how site-selected growth can be leveraged for the rational fabrication of different types of hybrid nanostructures, with an emphasis on the parameters that can be experimentally controlled to tailor the properties for various applications.

Niobium Oxides: The key role of hydroxylated surface on photocatalytic driven C–C reductive coupling of acetophenone

Aromatic diols play a pivotal role in various industries as crucial components of bulk feedstock and fine chemicals, particularly in pharmaceutical production. However, the complexity of the chemical reactions involved in their synthesis often poses challenges for achieving high yields and purity. This study introduces an alternative approach for the synthesis of 2,3-diphenylbutane-2,3-diol (DPB) and 2-phenylbutane-2,3-diol (PB) using niobium oxides as photocatalysts for C–C reductive coupling with acetophenone as the substrate. Niobium oxides were synthesized from commercially available niobic acid (HY-340) via calcination at various temperatures. The characterization data revealed the critical impact of thermal treatment on the acid-hydroxylated surface groups of niobic acid, which strongly influenced the photocatalytic performance. Therefore, niobic acid emerged as the most active photocatalyst, achieving yields of 32.0 % and 35.1 % for PB and DPB, respectively, after 2 h of UV irradiation. Control experiments were conducted in conjunction with electron paramagnetic resonance and electrochemical impedance measurements to elucidate the mechanistic pathways governing the formation of DPB and PB, and to shed light on the significant role played by the surface structure of niobic acid in influencing the photocatalytic performance. This study not only provides valuable insights into the synthesis of aromatic diols but also emphasizes the significance of tailoring the surface properties of niobium oxide catalysts to enhance reactivity in photochemical processes.

Monitoring the ionospheric conditions during the annular solar eclipse December 2019: A case study

This study investigates the ionospheric response to the December 26, 2019 annular solar eclipse over the southern tip of the Asia region, focusing on Malaysia, Sumatra, and Singapore. Utilizing data from GPS stations and ionosondes along the eclipse path, variations in Total Electron Content (TEC) and ionospheric foF2 parameters were analysed to assess the eclipse's impact. Results indicate a slight northward depletion of TEC, possibly linked to the Equatorial Ionization Anomaly (EIA), with up to −30% of depletions observed across all sites. Time delays in TEC and foF2 parameter responses suggest the influence of recombination and photochemical processes. Differences in depletion percentages between TEC and foF2 parameters may stem from production rate reductions during the eclipse. Post-sunset enhancements in TEC and foF2 parameters suggest the formation of ionospheric plasma blobs associated with Travelling Ionospheric Disturbances (TIDs) during the eclipse. While consistent with trends observed in prior studies, the study's findings highlight regional variations in ionospheric effects. This study enhances our understanding of ionospheric dynamics during solar eclipses and paves the way for further exploration in this area.

Antibacterial Activity of Sungkai Leaf Extract (Peronema canescens Jack) Against Streptococcus Pneumonia ATCC Bacteria. 49619 In Vitro

Pneumonia is an infectious disease of the respiratory tract that is transmitted through the air. Young leaves of the sungkai plant of the Verbenaceae tribe, traditionally often used as a cold medicine, worms (ringworms), prevent toothache by gargling, as a febrifuge. In addition, sungkai leaves are a traditional medicine to improve the immune system of patients with Covid-19. The purpose of this study was to determine the antibacterial activity of sungkai leaf extract in inhibiting the growth of Streptococcus pneumonia at bacteria.49619 The research methodology used was experimental. This research method starts with tool preparation, sampling, the extraction process, the photochemical process, and further extraction antibacterial activity testing is carried out by disk diffusion method using disc paper. The results of the study of the antibacterial activity of sungkai leaf extract have antibacterial activity in Streptococcus pneumonia atcc.49619 with a concentration of 25% categorized as medium, 50%, and 75% categorized as strong, while in Control + categorized as very strong. Based on the results of the conclusions showed that sungkai leaf extract has antibacterial activity.

Photo-cycloaddition reactions of vinyldiazo compounds

Heterocyclic rings are important structural scaffolds encountered in both natural and synthetic compounds, and their biological activity often depends on these motifs. They are predominantly accessible via cycloaddition reactions, realized by either thermal, photochemical, or catalytic means. Various starting materials are utilized for this purpose, and, among them, diazo compounds are often encountered, especially vinyldiazo compounds that give access to donor-acceptor cyclopropenes which engage in [2+n] cycloaddition reactions. Herein, we describe the development of photochemical processes that produce diverse heterocyclic scaffolds from multisubstituted oximidovinyldiazo compounds. High chemoselectivity, good functional group tolerance, and excellent scalability characterize this methodology, thus predisposing it for broader applications. Experimental and computational studies reveal that under light irradiation these diazo reagents selectively transform into cyclopropenes which engage in cycloaddition reactions with various dipoles, while under thermal conditions the formation of pyrazole from vinyldiazo compounds is favored.

Modeling and experimental verification for photodegradation in a spinning disk reactor

The spinning disk reactor has been regarded as a process intensification device in photochemical processes, which decreases the light path length by the thin film formation created by centrifugal force. A reliable reactor model was indispensable for the practical application of photoreactors. Our previous studies proposed a spinning disk reactor with elliptic-cylindrical and cylindrical spoilers for photochemical process intensification, and then hydrodynamic parameters of liquid film thickness, photon absorption rate, and residence time distribution were obtained. Based on the obtained parameters, herein, a reactor model was further established for the description of photodegradation reaction in the innovative spinning disk reactor. Different non-ideal flow models were employed during the model development, including the tanks-in-series model and axial dispersion model. The apparent reaction rate constant of a spinning disk reactor with spoilers was determined by the photon absorption rate, which was in the range of 0.088–0.268 s−1. The reactor model was verified by the experiments on photodegradation of Methylene Blue under different disk configurations and operating conditions. The degradation efficiency of Methylene Blue could reach up to 89.8 % in 25 min at N = 200 r/min, Q = 60 L/h, and I0 = 8 mW/cm2. The deviation between predicted and experimental Methylene Blue degradation efficiencies was within ± 20 %, confirming the rationality of the reactor model. The developed model lays the foundation for the scaling-up and commercial applications of the novel spinning disk reactors.

A light - Driven acidic positive feedback mechanism of sulfate formation

As the main source of atmospheric sulfate aerosol, the aqueous-phase oxidation of SO2 has been of great concern. Traditionally, the aqueous-phase oxidation of SO2 is considered a consumption process of atmospheric oxidation capacity; however, we report here that •OH radicals and other reactive oxygen species (ROS) can be generated in the photochemical reactions of bulk HSO3− solution. This •OH production pathway results in the fast sulfate formation in the photooxidation of dissolved SO2. The photochemical process is determined to be pH-dependent in which sulfate formation is promoted by decreasing pH. Hence, a light - driven acidic positive feedback mechanism is proposed that the oxidation of dissolved SO2 and the formation of •OH radicals have a synergistic promoting effect. These results indicate that the photochemistry of dissolved SO2 could be a missing source of aqueous •OH radicals as well as sulfate at regional to global scales.

Sources and formation of fine particles and organic aerosols during autumn-winter period in the southern edge of northern China plain

The North China Plain (NCP) experienced significant improvements in air quality in 2018–2022. However, severe pollution episodes still occur frequently during the cold season. The limitations of highly time-resolved measurements hinder understanding the sources and formation mechanisms of pollution episodes, especially the role of organic aerosols (OA). Therefore, we used a Time-of-Flight Aerosol Chemical Speciation Monitor to characterize the aerosol chemical species, variation, and sources of OA during autumn and winter in Luohe, a city in the southern part of the NCP. The results showed that nitrates and organics were the main species of fine particles (PM2.5), accounting for an average of 38.4% and 29.6% of its total mass, respectively. Furthermore, the positive matrix factorization model analyzed the OA in PM2.5 and identified three primary OA and secondary OA related to photochemistry. Primary OA was the dominant contributor throughout the study period (55%), increasing from 50% during the non-heating period to 59% during the heating period. The contribution of photochemically generated oxidized OA remained high (41%) during heavy pollution episodes in the heating period, indicating strong photochemical production during winter. Additionally, most aerosol species and OA factors showed distinct diurnal variations, with lower concentrations during the day, suggesting the influence of the planetary boundary layer and primary emissions. By analyzing the chemical species features of five heavy particulate matter pollution episodes during the study period, we identified three main driving mechanisms for severe pollution events: photochemical processing, photochemical and aqueous-phase production, and local emissions.

Environmental significance of PAH photoproduct formation: TiO2 nanoparticle influence, altered bioavailability, and potential photochemical mechanisms

Interactions between polycyclic aromatic hydrocarbons (PAHs) and titanium dioxide (TiO2) nanoparticles (NPs) can produce unforeseen photoproducts in the aqueous phase. Both PAHs and TiO2-NPs are well-studied and highly persistent environmental pollutants, but the consequences of PAH-TiO2-NP interactions are rarely explored. We investigated PAH photoproduct formation over time for benzo[a]pyrene (BaP), fluoranthene (FLT), and pyrene (PYR) in the presence of ultraviolet A (UVA) using a combination of analytical and computational methods including, identification of PAH photoproducts, assessment of expression profiles for gene indicators of PAH metabolism, and computational evaluation of the reaction mechanisms through which certain photoproducts might be formed. Chemical analyses identified diverse photoproducts, but all PAHs shared a primary photoproduct, 9,10-phenanthraquinone (9,10-PQ), regardless of TiO2-NP presence. The computed reaction mechanisms revealed the roles photodissociation and singlet oxygen chemistry likely play in PAH mediated photochemical processes that result in the congruent production of 9,10-PQ within this study. Our investigation of PAH photoproduct formation has provided substantial evidence of the many, diverse and congruent, photoproducts formed from physicochemically distinct PAHs and how TiO2-NPs influence bioavailability and time-related formation of PAH photoproducts.

A Low-Cost Ecofriendly Oxidation Process to Manufacture High-Performance Polymeric Biosurfactants Derived from Municipal Biowaste.

Biosurfactants account for about 12% of the global value of the surfactant market, which is currently dominated by synthetic surfactants obtained from fossil sources. Yet, the production of biosurfactants from renewable feedstock is bound to increase, driven by the increasing pressure from both society and governments for chemistry-based industries to become more ecofriendly and economically sustainable. A photo-chemical oxidation process is reported here, yielding new biosurfactants from urban biowaste in water that perform as a solvent and terminal oxidant reagent at room temperature without the addition of conventional oxidants and catalysts. Products with 200-500 kDa molecular weight are obtained. They lower the surface tension of water down to 34 mN/m at 0.5-2 g/L concentration. The estimated cost is rather low (0.1-1.5 EUR/kg), which is competitive with the cost of synthetic surfactants but much lower than the cost of the best-performing bacterial surfactants. For the implementation of the photo-chemical oxidation process at the industrial level, the results suggest that the new biosurfactants obtained in the present work may not reach the performance level of the best-performing bacterial surfactants capable of lowering the surface tension of water down to 28 mN/m. Yet, the biosurfactants produced by the photo-chemical process have a greater chance of being marketed on large scales.

Quantum Quality with Classical Cost: Ab Initio Nonadiabatic Dynamics Simulations Using the Mapping Approach to Surface Hopping.

Nonadiabatic dynamics methods are an essential tool for investigating photochemical processes. In the context of employing first-principles electronic structure techniques, such simulations can be carried out in a practical manner using semiclassical trajectory-based methods or wave packet approaches. While all approaches applicable to first-principles simulations are necessarily approximate, it is commonly thought that wave packet approaches offer inherent advantages over their semiclassical counterparts in terms of accuracy and that this trait simply comes at a higher computational cost. Here we demonstrate that the mapping approach to surface hopping (MASH), a recently introduced trajectory-based nonadiabatic dynamics method, can be efficiently applied in tandem with ab initio electronic structure. Our results even suggest that MASH may provide more accurate results than on-the-fly wave packet techniques, all at a much lower computational cost.

Observing low-altitude features in ozone concentrations in a shoreline environment via uncrewed aerial systems

Abstract. Ozone is a pollutant formed in the atmosphere by photochemical processes involving nitrogen oxides (NOx) and volatile organic compounds (VOCs) when exposed to sunlight. Tropospheric boundary layer ozone is regularly measured at ground stations and sampled infrequently through balloon, lidar, and crewed aircraft platforms, which have demonstrated characteristic patterns with altitude. Here, to better resolve vertical profiles of ozone within the atmospheric boundary layer, we developed and evaluated an uncrewed aircraft system (UAS) platform for measuring ozone and meteorological parameters of temperature, pressure, and humidity. To evaluate this approach, a UAS was flown with a portable ozone monitor and a meteorological temperature and humidity sensor to compare to tall tower measurements in northern Wisconsin. In June 2020, as a part of the WiscoDISCO20 campaign, a DJI M600 hexacopter UAS was flown with the same sensors to measure Lake Michigan shoreline ozone concentrations. This latter UAS experiment revealed a low-altitude structure in ozone concentrations in a shoreline environment showing the highest ozone at altitudes from 20–100 m a.g.l. These first such measurements of low-altitude ozone via a UAS in the Great Lakes region revealed a very shallow layer of ozone-rich air lying above the surface.