Unraveling the Mechanisms of the Excited-State Intermolecular Proton Transfer (ESPT) for a D-π-A Molecular Architecture

Precise revealing the mechanisms of excited-state intermolecular proton transfer (ESPT) and the corresponding geometrical relaxation upon photoexcitation and photoionization remains a formidable challenge. In this work, the compound (E)-4-(((4H-1,2,4-triazol-4-yl)imino)methyl)-2,6-dimethoxyphenol (TIMDP) adopting a D-π-A molecular architecture featuring a significant intramolecular charge transfer (ICT) effect has been designed. With the presence of perchloric acid (35 %), TIMDP can be dissolved through the formation of a HClO₄–H₂O–OH(TIMDP)–N(TIMDP) hydrogen-bonding bridge. At the ground state, the ICT effect is dominant, giving birth to crystals of TIMDP. Upon external stimuli (e.g., UV light irradiation, electro field), the excited state is achieved, which weakens the ICT effect, and significantly promotes the ESPT effect along the hydrogen-bonding bridge, resulting in crystals of [HTIMDP]⁺ ⋅ [H₂O] ⋅ [ClO₄]⁻. As a consequence, the mechanisms of the ESPT can be investigated, which distorted the D-π-A molecular architecture, tuned the emission color with the largest Stokes shift of 242 nm, and finally, high photoluminescence quantum yields (12 %) and long fluorescence lifetimes (8.6 μs) have achieved. These results not only provide new insight into ESPT mechanisms, but also open a new avenue for the design of efficient ESPT emitters.     

Reduction and pH dual‐responsive block copolymers containing pendent p‐nitrobenzyl carbamate functionalities: Synthesis and self‐assembly behavior

We report on the preparation of reduction‐responsive amphiphilic block copolymers containing pendent p‐nitrobenzyl carbamate (pNBC)‐caged primary amine moieties by reversible addition–fragmentation chain transfer (RAFT) radical polymerization using a poly(ethylene glycol)‐based macro‐RAFT agent. The block copolymers self‐assembled to form micelles or vesicles in water, depending on the length of hydrophobic block. Triggered by a chemical reductant, sodium dithionite, the pNBC moieties decomposed through a cascade 1,6‐elimination and decarboxylation reactions to liberate primary amine groups of the linkages, resulting in the disruption of the assemblies. The reduction sensitivity of assemblies was affected by the length of hydrophobic block and the structure of amino acid‐derived linkers. Using hydrophobic dye Nile red (NR) as a model drug, the polymeric assemblies were used as nanocarriers to evaluate the potential for drug delivery. The NR‐loaded nanoparticles demonstrated a reduction‐triggered release profile. Moreover, the liberation of amine groups converted the reduction‐responsive polymer into a pH‐sensitive polymer with which an accelerated release of NR was observed by simultaneous application of reduction and pH triggers. It is expected that these reduction‐responsive block copolymers can offer a new platform for intracellular drug delivery. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1333–1343     

Correlation analysis of cone calorimetry and microscale combustion calorimetry experiments

Flammability studies are conducted to evaluate the behavior of materials exposed to fire. In this study, microscale combustion calorimetry (MCC) and cone calorimetry methods were applied to acquire the flammability characteristics of red and grey extruded polystyrene (XPS) samples. To understand the effect of changes between parameters, Pearson’s correlation coefficient was used to examine their linear relationships. From the research, moderate and weak correlations were recorded between the total heat release rates from both methods for red and grey XPS, respectively. Plotting peak heat release rate against heat release temperature for MCC and ignition temperature for cone test showed that 25, 35 and 50 kW m^?2 incident heat fluxes of the cone test fall within 0.2 K s^?1 and 0.5 K s^?1 heating rates of MCC. Also, all the MCC parameters except char yield and total heat release presented good correlations with the cone calorimetry flammability characteristics. Hence, MCC could be used in conjunction with cone calorimetry to accurately and reliably assess the flammability of materials.

     

An organoantimony nitrate complex with azastibocine framework as water tolerant Lewis acid catalyst for the synthesis of 1,2-disubstitued benzimidazoles

A novel organoantimony complex of 6-cyclohexyl-6,7-dihydrodibenzo[c,f] [1,5]azastibocin-12(5H)-yl nitrate ( 2 ) was synthesized and systematically characterized by techniques such as NMR spectra, TG-DSC, and X-ray diffraction. It was found that the complex 2 exhibits relatively strong Lewis acidity (3.3 < Ho ≤ 4.8) and could be employed as a water tolerant Lewis acid catalyst for the synthesis of synthetically valuable benzimidazole derivatives starting from aldehydes and arylenediamines. This catalytic system shows excellent tolerance toward a wide variety of functional groups, such as methyl, methoxyl, fluoro, chloro, bromo, nitro, cyan, trifluoromethyl, 1-naphthaldehyde, furfural and n-butyl, together with facile reusability in 5 times scale enlarged synthesis.     

The metabolites and biotransformation pathways in vivo after oral administration of ocotillol,RT5, and PF11

Ocotillol, pseudo-ginsenoside RT5 (RT₅), and pseudo-ginsenoside F₁₁ (PF₁₁) are ocotillol-type saponins that have the same aglycone structure but with different numbers of glucose at the C-6 position. In this study, the metabolites of ocotillol, RT₅, and PF₁₁ in rat plasma, stomach, intestine, urine, and feces after oral administration were investigated by ultra-performance liquid chromatography coupled with time-of-flight mass spectrometry. The results showed that RT₅ was easily biotransformed into metabolites in vivo, whereas PF₁₁ and RT₅ were difficult to be biotransformed. Hydrogenation, dehydrogenation, dehydration, deglycosylation, deoxygenation, hydration, phosphorylation, deoxidation, glucuronidation, and reactions combining amino acid were speculated to be involved in the biotransformation of ocotillol, RT₅, and PF₁₁. Based on the structural analysis of metabolites, it was deduced that hydrogenation, dehydration, deoxidation, and reactions combining amino acid occurred on the aglycone structure, whereas deglycosylation, hydration, and phosphorylation occurred on the glycosyl chain. Further, metabolites in plasma, urine, feces, and tissues were different: First, glucuronidation products were found in urine, stomach, intestine, and feces, but not in plasma. Second, the ocotillol prototype was not identified in urine samples. Third, the RT₅ prototype was found in stomach, intestine, feces, and urine, but not in plasma.     

BowtieArene: A Dual Macrocycle Exhibiting Stimuli-Responsive Fluorescence

Although highly useful in supramolecular chemistry, pillararenes lack a fluorophore in their skeleton. Here we present BowtieArene, a novel fluorescent dual macrocycle, featuring a central tetraphenylethylene-derived fluorophore and two pillar-like, pentagon-shaped cavities which are comparable to pillar[5]arene. This concisely prepared, figure-of-eight molecule exhibits vapor absorption and host–guest capabilities, as well as intriguing switchable fluorescence. The fluorochromism of BowtieArene can be triggered by multiple external stimuli including solvent, vapor, and mechanical force, with excellent reversibility and stability. Experimental and theoretical evidence indicate that the fluorochromism should be closely related to molecular packing.     

Li[LiCs2Cl][Ga3S6]: A Nanoporous Framework of GaS4 Tetrahedra with Excellent Nonlinear Optical Performance

A large nonlinear optical (NLO) coefficient and a wide band gap are two crucial but contradictory parameters that are difficult to achieve simultaneously in a single infrared (IR) NLO compound. A salt‐inclusion chalcogenide (SIC), Li[LiCs₂Cl][Ga₃S₆] ( 1 ), was prepared that presents a nanosized tunnel framework constructed from monotype chalcogenide tetrahedra. Highly oriented covalent GaS₄ tetrahedra in the host lead to a moderate second harmonic generation response (0.7 AgGaS₂), and ionic guests effectively broaden the band gap to the widest value (4.18 eV) among all IR NLO chalcogenides, thereby achieving a remarkable balance between NLO efficiency and band gap.     

N-heterocyclic carbene-catalyzed regio- and stereoselective hydrothiolation reaction of alkynes

N-heterocyclic carbenes (NHCs) have been utilized as Brønsted base to catalyze the hydrothiolation reaction between alkynes and thiols to produce the vinyl sulfides stereoselectively.