Cyclohexadiene Revisited: A Time-Resolved Photoelectron Spectroscopy and <i>ab Initio</i> Study

We have reinvestigated the excited state dynamics of cyclohexa-1,3-diene (CHD) with time-resolved photoelectron spectroscopy and fewest switches surface hopping molecular dynamics based on linear response time-dependent density functional theory after excitation to the lowest lying ππ* (1B) state. The combination of both theory and experiment revealed several new results: First, the dynamics progress on one single excited state surface. After an incubation time of 35 ± 10 fs on the excited state, the dynamics proceed to the ground state in an additional 60 ± 10 fs, either via a conrotatory ring-opening to hexatriene or back to the CHD ground state. Moreover, ring-opening predominantly occurs when the wavepacket crosses the region of strong nonadiabatic coupling with a positive velocity in the bond alternation coordinate. After 100 fs, trajectories remaining in the excited state must return to the CHD ground state. This extra time delay induces a revival of the photoelectron signal and is an experimental confirmation of the previously formulated model of two parallel reaction channels with distinct time constants. Finally, our simulations suggest that after the initially formed <i>cis</i>-Z-<i>cis</i> HT rotamer the <i>trans</i>-Z-<i>trans</i> isomer is formed, before the thermodynamical equilibrium of three possible rotamers is reached after 1 ps

The Alkaline Hydrolysis of Sulfonate Esters: Challenges in Interpreting Experimental and Theoretical Data

Sulfonate ester hydrolysis has been the subject of recent debate, with experimental evidence interpreted in terms of both stepwise and concerted mechanisms. In particular, a recent study of the alkaline hydrolysis of a series of benzene arylsulfonates (Babtie et al., <i>Org. Biomol. Chem.</i> <i>10</i>, <b>2012</b>, 8095) presented a nonlinear Brønsted plot, which was explained in terms of a change from a stepwise mechanism involving a pentavalent intermediate for poorer leaving groups to a fully concerted mechanism for good leaving groups and supported by a theoretical study. In the present work, we have performed a detailed computational study of the hydrolysis of these compounds and find no computational evidence for a thermodynamically stable intermediate for any of these compounds. Additionally, we have extended the experimental data to include pyridine-3-yl benzene sulfonate and its <i>N</i>-oxide and <i>N</i>-methylpyridinium derivatives. Inclusion of these compounds converts the Brønsted plot to a moderately scattered but linear correlation and gives a very good Hammett correlation. These data suggest a concerted pathway for this reaction that proceeds via an early transition state with little bond cleavage to the leaving group, highlighting the care that needs to be taken with the interpretation of experimental and especially theoretical data

Pressure-Induced Emission from All-Inorganic Two-Dimensional Vacancy-Ordered Lead-Free Metal Halide Perovskite Nanocrystals

Although seeking an effective strategy for further improving their optical properties is a great challenge, two-dimensional (2D) halide perovskites have attracted a significant amount of attention because of their performance. In this regard, the pressure-induced emission accompanied by a remarkable pressure-enhanced emission is achieved without a phase transition in 2D vacancy-ordered perovskite Cs3Bi2Cl9 nanocrystals (NCs). Note that the initial Cs3Bi2Cl9 NCs possess extremely strong electron–phonon coupling, leading to the easy annihilation of trapped excitons by the phonon. Upon compression, pressure could effectively suppress phonon-assisted nonradiative decay and give rise to an intriguing emission from “0” to “1”. Both the weakened electron–phonon coupling and the relaxed halide octahedral distortion benefiting from the vacancy-ordered structure contributed to the subsequent enhanced emission. This work not only elucidates the underlying photophysical mechanism but also identifies pressure engineering as a robust means for improving their potential applications in environmentally friendly solid-state lighting at extremes

Near-Ultraviolet to Near-Infrared Fluorescent Nitrogen-Doped Carbon Dots with Two-Photon and Piezochromic Luminescence

Carbon dots (CDs) have gained intensive interests owing to their unique structure and excellent optoelectronic performances. However, to acquire CDs with a broadband emission spectrum still remains an issue. In this work, nitrogen-doped CDs (N-CDs) with near-ultraviolet (NUV), visible, and near-infrared (NIR) emission were synthesized via one-pot solvothermal strategy, and the excitation-independent NUV and NIR emission and excitation-dependent visible emission were observed in the photoluminescence (PL) spectra of N-CDs. Moreover, the as-synthesized N-CDs displayed two-photon fluorescence emission. It is important to note that N-CDs also exhibited piezochromic luminescence with reversibility, in which the red- and blue-shifted PL with increasing applied pressure (0.07–5.18 GPa) and the red- and blue-shifted PL with releasing applied pressure (5.18 GPa to 1 atm) were developed for the first time. Combined with good hydrophilicity, high photobleaching resistance, and low toxicity, the piezochromic luminescence would greatly boost the valuable applications of N-CDs

Effects of TNF-α on cell viability, inflammatory cytokines and ERS-related molecules.

<p><b>A.</b> Cell viability is expressed as an OD value. <b>B.</b> The levels of sICAM1 in cell culture supernatants. <b>C.</b> Representative Western blot results showing ICAM1, MMP9, GRP78, ATF4, cleaved-caspase12, p-PERK and PERK protein expression. The results are expressed as the means ±SD, n = 6. ^aaP<0.01, compared with the control group; ^bbP<0.01, compared with the 1 ng/mL TNF-α group; ^ccP<0.01, compared with the 5 ng/mL TNF-α group. EP, ethyl pyruvate; OD, optical density.</p

Effects of PERK siRNA on TNF-α-induced inflammatory cytokines in cell culture supernatants.

<p><b>A.</b> The adhesion of U937 monocytes to HUVECs. <b>B.</b> The levels of sICAM1 production in cell culture supernatants. <b>C.</b> The levels of MCP-1 production in cell culture supernatants. The results are expressed as the means ± SD, n = 6. ^aaP<0.01, compared with the control siRNA group; ^bbP<0.01, compared with the control siRNA+TNF-α group; ^ccP<0.01, compared with the PERK siRNA+TNF-α group. EP, ethyl pyruvate.</p

Effects of EP on TNF-α-induced cell viability, monocyte adhesion and inflammatory cytokines in cell culture supernatants.

<p><b>A.</b> Cell viability is expressed as an OD value. <b>B.</b> The adhesion of U937 monocytes to HUVECs. <b>C.</b> The levels of sICAM1 production in cell culture supernatants. <b>D.</b> The levels of IL-8 production in cell culture supernatants. <b>E.</b> The levels of MCP-1 production in cell culture supernatants. <b>F.</b> The levels of sE-selectin production in cell culture supernatants. The results are expressed as the means ± SD, n = 6. ^aaP<0.01, compared with the control group; ^bbP<0.01, compared with the TNF-α group; ^ccP<0.01, compared with the 1 mM EP+TNF-α group; ^ddP<0.01, compared with the 5 mM EP+TNF-α group. EP, ethyl pyruvate; OD, optical density.</p

Effects of EP and THA co-treatment on TNF-α-induced inflammatory cytokines in cell culture supernatants.

<p><b>A.</b> The adhesion of U937 monocytes to HUVECs. <b>B.</b> The levels of sICAM1 production in cell culture supernatants. <b>C.</b> The levels of MCP-1 production in cell culture supernatants. The results are expressed as the means ± SD, n = 6. ^aaP<0.01, compared with the TNF-α group; ^bbP<0.01, compared with the EP+TNF-α group; ^ccP<0.01, compared with the EP+THA+TNF-α group. EP, ethyl pyruvate; THA, thapsigargin.</p

Effects of EP on the TNF-α-induced inflammatory protein and ERS-related molecules in HUVECs.

<p>Representative Western blot results showingICAM1, MMP9, GRP78, ATF4, cleaved-caspase12, p-PERK and PERK protein expression. The results are expressed as the means ± SD, n = 6. ^aaP<0.01, compared with the control group; ^bbP<0.01, compared with the TNF-α group; ^ccP<0.01, compared with the 1 mM EP+TNF-α group; ^ddP<0.01, compared with the 5 mM EP+TNF-α group. EP, ethyl pyruvate.</p