Significant differences between solid state and solution photochemistry and photophysics of mesogenic organometallic gold complexes

Five new gold complexes 4-ROC6H4C≡CAuN≡CC6H4-4-OR′ (R/R′ = CH3/C9H19 (C1N9 ), C15H31/C9H19 (C15N9 ), C6H13/C15H31 (C6N15 ), C9H19/C15H31 (C9N15 ), C12H25/C15H31 (C12N15 )) were synthesized and characterized (1H and 13C NMR, IR, Raman spectroscopy, and high resolution mass spectrometry). Their organized smectic phases were investigated by TGA, DSC, powder XRD, and polarized light optical microscopy, and the solids are found to have crystalline and amorphous domains. No evidence for Au•••Au interactions was observed. The steady state and time-resolved absorption and emission properties at 298 and 77 K were examined, and surprisingly, the excited lifetime of the triplet excited state in the solid state is extremely short-lived (<100 ps) in comparison with the microsecond time scale recorded for the solution and at 77 K. The photosensitization of 1O2 was observed in solution but not in the solid state. The nature of the singlet (ligand-to-ligand charge transfer) and triplet (ethynyl/intraligand ππ*) excited states were assessed using DFT and TD-DFT computations. The thermal and UV-photochemical formation of gold nanoparticles were performed in solution (slow) and in the solid state (faster). The thermally generated nanoparticles are found to be larger (2–20 nm; TEM) and exhibit well-defined shapes, whereas the photochemically generated ones are smaller (1–10 nm) and show ill-defined shapes.

Insights into the abnormal increase of ozone during COVID-19 in a typical urban city of China

The outbreak of COVID-19 promoted strict restrictions to human activities in China, which led to dramatic decrease in most air pollutant concentrations (e.g., PM2.5, PM10, NOx, SO2, and CO). However, abnormal increase of ozone (O3) concentrations was found during the lockdown period in most urban areas of China. In this study, we conducted a field measurement targeting ozone and its key precursors by utilizing a novel proton transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS) in Changzhou, which is representative for the Yangtze River Delta (YRD) city cluster of China. We further applied the integrated methodology including machine learning, observation-based model (OBM), and sensitivity analysis to get insights into the reasons causing the abnormal increase of ozone. Major findings include: (1) By deweathered calculation, we found changes in precursor emissions contributed 5.1 ppbv to the observed O3 during the Full-lockdown period, while meteorological conditions only contributed 0.5 ppbv to the O3 changes. (2) By using an OBM model, we found that although significant reduction of O3 precursors was observed during Full-lockdown period, the photochemical formation of O3 was stronger than that during the Pre-lockdown period. (3) The NOx / VOCs ratio dropped dramatically from 1.84 during Pre-lockdown to 0.79 in Full-lockdown period, which switched O3 formation from VOCs-limited regime to the conjunction of NOx- and VOC-limited regime. Additionally, the decrease in NOx / VOCs ratio during Full-lockdown period was supposed to increase the MeanO3 by 2.4 ppbv. Results of this study investigate insights into the relationship between O3 and its precursors in urban area, demonstrating reasons causing the abnormal increase of O3 in most urban areas of China during the COVID-19 lock-down period. This study also underlines the necessity of controlling anthropogenic OVOCs, alkenes, and aromatics in the sustained campaign of reducing O3 pollution in China.

Ozone Continues to Increase in East Asia Despite Decreasing NO2: Causes and Abatements

Space-borne ozone (O3) measurements have indicated consistent positive trends across the entire Asia–Pacific region despite the considerable reduction of NOx since 2000s. The rate of increase in O3 derived from lower free tropospheric column measurements was observed to be 0.21 ± 0.05 DU/decade during 2005–2018. Our space-borne-based diagnosis of the nonlinear photochemical formation regimes, NOx-limited and NOx-saturated, show that O3 chemistry is undergoing a transitional process to the NOx-limited regime throughout most of the Asian region. Nevertheless, NOx-saturated conditions persist at present in and over eight major megacities. These NOx-saturated conditions in megacities contribute to the increased O3 due to NOx reduction, which could also affect the enhanced O3 concentrations throughout the Asia–Pacific region via long-range transport. This indicates that VOC limits along with NOx reductions are needed in megacities in the short term to reduce O3 levels. Moreover, NOx saturation in major megacities will continue until 2025, according to the forecast emission scenarios from the Intergovernmental Panel on Climate Change (IPCC). These scenarios gradually shift nearly all cities to the NOx-limited regime by 2050 with the exception of few cities under IPCC RCP8.5. Thus, continued reductions in NOx will be a key factor in reducing O3 in the long term.

Assessing the Source of the Photochemical Formation of Hydroxylating Species from Dissolved Organic Matter Using Model Sensitizers

Dissolved organic matter (DOM) is ubiquitous in natural waters and can facilitate the chemi-cal transformation of many contaminants through the photochemical production of reactive inter-mediates, such as singlet oxygen (1O2),...