Optical Properties and Photo‐Oxidation of Tetraphenylethene‐Based Fluorophores

We report the optical properties of tetraphenylethene (TPE) and other TPE derivatives functionalised with an octyl group (TPE‐OCT) and polyethyleneglycol group (TPE‐PEG) in the side chain. We compared TPE‐OCT and TPE‐PEG with TPE in both organic solvents and under aqueous conditions. All materials exhibit aggregation‐induced emission, however, uncommonly, TPE‐PEG seems to aggregate in aqueous solution with enhanced photoluminescence quantum efficiency (PLQE) relative to that in organic solvents. All three materials can be photo‐oxidised in solution to their diphenylphenanthrene derivative by irradiation with UV light (at both ≈1 and ≈5 mW cm^?2), with a subsequent enhancement in PL efficiency. The electron‐donating ether group increases the rate of oxidation relative to bare TPE and also photo‐oxidation was shown to be solvent and concentration dependent. Finally, photo‐oxidation was also demonstrated in the aggregate state.     

Pd‐Catalyzed Reaction of Allyl Carbonate with Polyols: The Role of CO2 in Transesterification versus Etherification of Glycerol

An intermolecular Pd/PPh₃‐catalyzed transesterification of diallyl carbonate with glycerol to generate glycerol carbonate has been developed. Analysis of the reaction kinetics in THF indicates a first‐order dependence on Pd and diallyl carbonate, that the Pd bears two phosphines during the turnover limiting event, and that increasing the glycerol concentration inhibits reaction, possibly via change in the polarity of the medium. ¹³C isotopic labeling studies demonstrate that the Pd‐catalyzed transesterification requires at least one allyl carbonate moiety and that there is rapid equilibrium of the allyl carbonate with CO₂ in solution, even when present only at low concentrations. A mechanism that is consistent with these results involves oxidative addition of the allyl carbonate to Pd followed by reversible decarboxylation, with the intermediate η¹‐ and η³‐allyl Pd alkoxides mediating direct and indirect transesterification reactions with the glycerol. Using this model, successful simulations of the kinetics of reactions conducted under atmospheres of N₂ or CO₂ could be achieved, including switching in selectivity between etherification and transesterification in the early stages of reaction. Reactions with the higher polyols threitol and erythritol are also efficient, generating the terminal (1,2) monocarbonates with high selectivity.     

Heterotermetallic Indium Lithium Halostannates: Low‐Temperature Single‐Source Precursors for Tin‐Rich Indium Tin Oxides and Their Application for Thin‐Film Transistors

The syntheses and structural elucidation of dimeric [Sn(OCyHex)₂] ( 1 ), its corresponding (cyclohexoxy)alkalistannates(II) [{M(OCyHex)₃Sn}₂] (M=Li ( 2 ), Na ( 3 ), K ( 4 )), and of the first heteroleptic heterotermetallic Li/In/Sn–haloalkoxide clusters [X₂In{LiSn₂(OCyHex)₆}] (X=Br ( 5 ), Cl ( 6 )) with a double seco‐norcubane core are reported. They represent suitable precursors for new amorphous indium tin oxide (ITO) materials as transparent conducting oxides with drastically reduced concentrations of expensive indium, while maintaining their high electrical performance. In fact, compounds 5 and 6 were successfully degraded under dry synthetic air at relatively low temperature, resulting in new semiconducting tin‐rich ITOs homogeneously dispersed in a tin oxide/lithium oxide matrix. The obtained particles were investigated and characterised by different analytical techniques, such as powder XRD, IR spectroscopy, SEM, TEM and energy‐dispersive X‐ray spectroscopy (EDX). The analytical data confirm that the final materials consist of tin‐containing indium oxide embedded in an amorphous tin oxide matrix. The typical broadening and shift of the observed indium oxide reflections to higher 2θ values in the powder XRD pattern clearly indicated that tin centres were successfully incorporated into the In₂O₃ lattice and partially occupied In³⁺ sites. Investigations by EDX mapping proved that Sn was homogeneously distributed in the final materials. Thin‐film field‐effect transistors (FETs) were fabricated by spin‐coating of silicon wafers with solutions of 5 in toluene and subsequent calcination under dry air (25–700 °C). The FETs prepared with precursor 5 exhibited excellent performances, as shown by a charge‐carrier mobility of 6.36×10^?1 cm² V^?1 s (calcination at 250 °C) and an on/off current ratio of 10⁶.     

Comparison of the Peroxidase‐Like Activity of Unmodified,Amino‐Modified,and Citrate‐Capped Gold Nanoparticles

The origin of the peroxidase‐like activity of gold nanoparticles and the impact of surface modification are studied. Furthermore, some influencing factors, such as fabrication process, redox property of the modifier, and charge property of the substrate, are investigated. Compared to amino‐modified or citrate‐capped gold nanoparticles, unmodified gold nanoparticles show significantly higher catalytic activity toward peroxidase substrates, that is, the superficial gold atoms are a contributing factor to the observed peroxidase‐like activity. The different catalytic activities of amino‐modified and citrate‐capped gold nanoparticles toward 3,3′,5,5′‐tetramethylbenzidine (TMB) and 2,2′‐azino‐bis(3‐ethylbenzothiazoline‐6‐sulfonic acid) diammonium salt (ABTS) show that the charge characteristics of the nanoparticles and the substrate also play an important role in the catalytic reactions.     

Asymmetric Nucleophilic Monofluorobenzylation of Carbonyl Compounds: Synthesis of Enantiopure vic‐Fluorohydrins and α‐Fluorobenzylketones

Asymmetric nucleophilic monofluoroalkylation of a broad range of aldehydes with an α‐fluoro‐γ‐sulfinylbenzyl carbanion takes place with complete control of the facial selectivity at the carbanion and good to high anti‐diastereoselectivity to give easily separable mixtures of two optically pure 1,2‐fluorohydrin derivatives (up to 24:1 anti/syn). Separation and removal of the p‐tolylsulfinyl group with tBuLi provides enantiomerically pure anti‐1,2‐disubstituted‐1,2‐fluorohydrins, whereas α‐fluorobenzylketones can be obtained by desulfinylation of the mixture followed by pyridinium chlorochromate oxidation (one‐pot process).     

Intracrystalline Diffusion in Mesoporous Zeolites

Specially synthesized extra‐large crystallites of zeolite LTA with intentionally added mesoporosity are used for an in‐depth study of guest diffusion in hierarchical nanoporous materials by the pulsed field gradient NMR technique. Using propane as a guest molecule, intracrystalline mass transfer is demonstrated to be adequately described by a single effective diffusivity resulting from the weighted average of the diffusivities in the two (micro‐ and meso‐) pore spaces. Gas‐kinetic order‐of‐magnitude estimates of the diffusivities are in satisfactory agreement with the experimental data and are thus shown to provide a straightforward means for predicting and quantifying the benefit of hierarchically structured nanoporous materials in comparison with their purely microporous equivalent.     

Photoactivated Nitrene Chemistry to Prepare Gold Nanoparticle Hybrids with Carbonaceous Materials

Photolysis of organic solvent soluble aryl azide‐modified gold nanoparticles (N₃‐AuNPs) with a core size of 4.6±1.6 nm results in the generation of interfacial reactive nitrene intermediates. The high reactivity of the nitrenes is utilized to tether the AuNP to the native surface of carbon nanotubes, and reduce graphene oxide and micro‐diamond powder, likely via addition to π‐conjugated carbon skeleton or insertion into the functionalities at the surface, to yield the desired hybrid material without the need for pretreatment of the surface. The AuNP‐covalent hybrid materials are robust in that they survive vigorous washing and sonication. In the absence of photolysis no attachment occurs with the same N₃‐AuNP. The nanohybrid AuNP‐nanohybrid materials are characterized using a combination of TEM, powder XRD, XPS and UV/Vis and IR spectroscopies. All of the characterization studies confirm the uniform incorporation of the AuNP on the irradiated substrates.     

Theoretical Insight into the Origin of Large Stokes Shift and Photophysical Properties of Anilido‐Pyridine Boron Difluoride Dyes

The geometric and electronic structures and photophysical properties of anilido‐pyridine boron difluoride dyes 1 – 4 , a series of scarce 4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BODIPY) derivatives with large Stokes shift, are investigated by employing density functional theory (DFT) and time‐dependent DFT (TD‐DFT) calculations to shed light on the origin of their large Stokes shifts. To this end, a suitable functional is first determined based on functional tests and a recently proposed index—the charge‐transfer distance. It is found that PBE0 provides satisfactory overall results. An in‐depth insight into Huang–Rhys (HR) factors, Wiberg bond indices, and transition density matrices is provided to scrutinize the geometric distortions and the character of excited states pertaining to absorption and emission. The results show that the pronounced geometric distortion due to the rotation of unlocked phenyl groups and intramolecular charge transfer are responsible for the large Stokes shift of 1 and 2 , while 3 shows a relatively blue‐shifted emission wavelength due to its mild geometric distortion upon photoemission, although it has a comparable energy gap to 1 . Finally, compound 4 , which is designed to realize the rare red emission in BODIPY derivatives, shows desirable and expected properties, such as high Stokes shift (4847 cm^?1), red emission at 660 nm, and reasonable fluorescence efficiency. These properties give it great potential as an ideal emitter in organic light‐emitting diodes. The theoretical results could complement and assist in the development of BODIPY‐based dyes with both large Stokes shift and high quantum efficiency.     

Kinetics of Iterative Carbohydrate Transfer to Polysaccharide Catalyzed by Chondroitin Polymerase on a Highly Sensitive Flow‐Type 27 MHz Quartz‐Crystal Microbalance

Using a highly sensitive flow‐type 27 MHz quartz crystal microbalance, we could detect a small mass change during stepwise and alternating one‐sugar transfer of glucuronic acid (GlcA) and N‐acetylgalactosamine (GalNAc) to an acceptor, catalyzed by chondroitin polymerase from Escherichia coli strain K4 (K4CP), and analyze the elongation mechanism of K4CP. K4CP was found to bind strongly to a chondroitin acceptor (K_d=0.97 μM ). Although the binding affinity and the catalytic rate constant for each monomer were considerably different, the apparent catalytic efficiency (k_cat/K_m) was similar (6.3×10⁴ M ^?1 s^?1 for GlcA transfer and 3.4×10⁴ M ^?1 s^?1 for the GalNAc transfer). This is reasonable for the smooth alternating elongation of GlcA and GalNAc on the acceptor. This is the first study to report the determination of kinetic parameters for enzymatic, alternated, sugar elongation.