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1. Naphthalene‐Derived Secondary Organic Aerosols Interfacial Photosensitizing Properties

   https://doi.org/10.1029/2021GL093465  

   Wang, Xinke ; Gemayel, Rachel ; Baboomian, Vahe J. ; Li, Kangwei ; Boreave, Antoinette ; Dubois, Clement ; Tomaz, Sophie ; Perrier, Sebastien ; Nizkorodov, Sergey A. ; George, Christian ( July 2021 , Geophysical Research Letters)

   We investigated the photosensitizing properties of secondary organic aerosol (SOA) formed during the hydroxyl radical (OH) initiated oxidation of naphthalene. This SOA was injected into an aerosol flow tube and exposed to UV radiation and gaseous volatile organic compounds or sulfur dioxide (SO₂). The aerosol particles were observed to grow in size by photosensitized uptake of d‐limonene and β‐pinene. In the presence of SO₂, a photosensitized production (0.2–0.3 µg m⁻³ h⁻¹) of sulfate was observed at all relative humidity (RH) levels. Some sulfate also formed on particles in the dark, probably due to the presence of organic peroxides. The dark and photochemical pathways exhibited different trends with RH, unraveling different contributions from bulk and surface chemistry. As naphthalene and other polycyclic aromatics are important SOA precursors in the urban and suburban areas, these dark and photosensitized reactions are likely to play an important role in sulfate and SOA formation.

    

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2. Photosensitized Reactions of a Phenolic Carbonyl from Wood Combustion in the Aqueous Phase—Chemical Evolution and Light Absorption Properties of AqSOA

   https://doi.org/10.1021/acs.est.0c07581  

   Jiang, Wenqing ; Misovich, Maria V. ; Hettiyadura, Anusha P. ; Laskin, Alexander ; McFall, Alexander S. ; Anastasio, Cort ; Zhang, Qi ( January 2021 , Environmental Science & Technology)

   null (Ed.)

   Guaiacyl acetone (GA) is a phenolic carbonyl emitted in significant quantities by wood combustion that undergoes rapid aqueous-phase oxidation to produce aqueous secondary organic aerosol (aqSOA). We investigate the photosensitized oxidation of GA by an organic triplet excited state (3C*) and the formation and aging of the resulting aqSOA in wood smoke-influenced fog/cloud water. The chemical transformations of the aqSOA were characterized in situ using a high-resolution time-of-flight aerosol mass spectrometer. Additionally, aqSOA samples collected over different time periods were analyzed using high-performance liquid chromatography coupled with a photodiode array detector and a high-resolution Orbitrap mass spectrometer (HPLC-PDA-HRMS) to provide details on the molecular composition and optical properties of brown carbon (BrC) chromophores. Our results show efficient formation of aqSOA from GA, with an average mass yield around 80%. The composition and BrC properties of the aqSOA changed significantly over the course of reaction. Three generations of aqSOA products were identified via Positive Matrix Factorization analysis of the AMS data. Oligomerization and functionalization dominated the production of the first-generation aqSOA, whereas fragmentation and ring-opening reactions controlled the formation of more oxidized second- and third-generation products. Significant formation of BrC was observed in the early stages of the photoreaction, while organic acids were produced throughout the experiment. High-molecular-weight molecules (m/z > 180) with high aromaticity were identified via HPLC-PDA-HRMS and were found to account for a majority of the UV-vis absorption of the aqSOA. 

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3. Quenching of ketone triplet excited states by atmospheric halides

   https://doi.org/10.1039/d0ea00011f  

   Gemayel, R. ; Emmelin, C. ; Perrier, S. ; Tomaz, S. ; Baboomian, V. J. ; Fishman, D. A. ; Nizkorodov, S. A. ; Dumas, S. ; George, C. ( January 2021 , Environmental Science: Atmospheres)

   null (Ed.)

   The photosensitized chemistry of three aromatic ketones (xanthone, flavone, and acetophenone) and also of secondary organic aerosol (SOA) arising from the photo-oxidation of naphthalene was investigated by means of transient absorption spectroscopy. Halide ions were selected to probe the reactivity of the generated triplet states. The quenching rate constants ranged from 10 9 M −1 s −1 with iodide ions to less than 10 5 M −1 s −1 with chloride ions. The halide-triplet state interactions produced the corresponding radical anion (X 2 ˙ − ) along with halogenated and more oxidized organic compounds as identified by liquid chromatography and mass spectrometry. Deoxygenated naphthalene SOA solutions showed strong transient absorption at 420 nm when excited at 355 nm, and were also quenched by iodide ions similar to the single compound experiments indicating that compounds in naphthalene SOA can act as photosensitizers. Combining the study of these individual and known photosensitizers with those formed in the atmosphere (in this case through the oxidation of naphthalene) demonstrates that tropospheric photosensitization may involve a large variety of compounds of primary or secondary nature and will introduce new, unconsidered chemical pathways that impact atmospheric multiphase chemistry. 

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4. A five-coordinate cobalt bis(dithiolene)–phosphine complex [Co(pdt) 2 (PTA)] (pdt = phenyldithiolene; PTA = 1,3,5-triaza-7-phosphaadamantane)

   https://doi.org/10.1107/S2056989020005447  

   Williams, DaShawn ; Brannon, Jacob P. ; Chandrasekaran, Perumalreddy ; Stieber, S. Chantal ( May 2020 , Acta Crystallographica Section E Crystallographic Communications)

   The title compound, bis(1,2-diphenyl-2-sulfanylideneethanethiolato-κ 2 S , S ′)(1,3,5-triaza-7-phosphaadamantane-κ P )cobalt(II) dichloromethane hemisolvate, [Co(pdt) 2 (PTA)]·0.5C 2 H 4 Cl 2 or [Co(C 14 H 10 S 2 ) 2 (C 6 H 12 N 3 P)]·0.5C 2 H 4 Cl 2 , contains two phenyldithiolene (pdt) ligands and a 1,3,5-triaza-7-phosphaadamantane (PTA) ligand bound to cobalt with the solvent 1,2-dichloroethane molecule located on an inversion center. The cobalt core exhibits an approximately square-pyramidal geometry with partially reduced thienyl radical monoanionic ligands. The supramolecular network is consolidated by hydrogen-bonding interactions primarily with nitrogen, sulfur and chlorine atoms, as well as parallel displaced π-stacking of the aryl rings. The UV–vis, IR, and CV data are also consistent with monoanionic dithiolene ligands and an overall Co II oxidation state. 

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5. Air‐Stable Silicon Nanocrystal‐Based Photon Upconversion

   https://doi.org/10.1002/adom.202100453  

   Xia, Pan ; Schwan, Joseph ; Dugger, Thomas W. ; Mangolini, Lorenzo ; Tang, Ming Lee ( June 2021 , Advanced Optical Materials)

   Photon upconversion may have the highest impact in biological applications because incoming photons transparent to tissue can be combined to make visible light useful for photodynamic therapy and imaging. The ability to use semiconductor nanocrystals as light absorbers for photon upconversion is important because their strong absorption profiles are synthetically tunable. In particular, the use of earth‐abundant, environmentally benign silicon quantum dots (QDs) as light absorbers for photon upconversion is very attractive. In this work, the authors demonstrate a general strategy employing both physical and chemical barriers to achieve air‐stable fusion of triplet excitons photosensitized by silicon QDs, crucial to practical applications of photon upconversion. Gel permeation chromatography (GPC) and dynamic light scattering (DLS) show that thermal hydrosilylation critical for colloidal stability and efficient triplet energy transfer creates a polymeric barrier to oxygen. This kinetic barrier to oxygen arises from the presence of cross‐linked surfactants and is complemented by the sacrificial oxidation of silicon QDs itself. Photon upconversion lasted longer than 4 days with quantum yields (QYs) as high as 7.5% (out of a maximum of 50%) using Si QD light absorbers with diphenylanthracene in methyl oleate. Oil‐in‐water micelles are air‐stable for 2 days with absolute upconversion QYs of 5.5%.

    

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