The Non-Ancillary Nature of Trimethylsilylamide Substituents in Boranes and Borinium Cations

The known boranes (R(Me₃Si)N)₂BF (R=Me₃Si 1 , tBu 2 , C₆F₅ 3 , o-tol 4 , Mes 5 , Dipp 6 ) and borinium salts (R(Me₃Si)N)₂B][B(C₆F₅)₄] (R=Me₃Si 7 , tBu 8 ) are prepared and fully characterized. Compound 7 is shown to react with phosphines to generate [R₃PSiMe₃]⁺ and [R₃PH]⁺ (R=Me, tBu). Efforts to generate related borinium cations via fluoride abstraction from (R(Me₃Si)N)₂BF (R=C₆F₅ 3 , o-tol 4 , Mes 5 ) gave complex mixtures suggesting multiple reaction pathways. However for R=Dipp 6 , the species [(μ-F)(SiMe₂N(Dipp))₂BMe][B(C₆F₅)₄] was isolated as the major product, indicating methyl abstraction from silicon and F/Me exchange on boron. These observations together with state-of-the-art DFT mechanistic studies reveal that the trimethylsilyl-substituents do not behave as ancillary subsitutents but rather act as sources of proton, SiMe₃ and methyl groups.     

Pyrimidoquinazolinophenanthroline Opens Next Chapter in Design of Bridging Ligands for Artificial Photosynthesis**

The synthesis and detailed characterization of a new Ru polypyridine complex containing a heteroditopic bridging ligand with previously unexplored metal-metal distances is presented. Due to the twisted geometry of the novel ligand, the resultant division of the ligand in two distinct subunits leads to steady state as well as excited state properties of the corresponding mononuclear Ru(II) polypyridine complex resembling those of prototype [Ru(bpy)₃]²⁺ (bpy=2,2'-bipyridine). The localization of the initially optically excited and the nature of the long-lived excited states on the Ru-facing ligand spheres is evaluated by resonance Raman and fs-TA spectroscopy, respectively, and supported by DFT and TDDFT calculations. Coordination of a second metal (Zn or Rh) to the available bis-pyrimidyl-like coordination sphere strongly influences the frontier orbitals, apparent by, for example, luminescence quenching. Thus, the new bridging ligand motif offers electronic properties, which can be adjusted by the nature of the second metal center. Using the heterodinuclear Ru−Rh complex, visible light-driven reduction of NAD⁺ to NADH was achieved, highlighting the potential of this system for photocatalytic applications.     

Influence of Pt Alloying on the Fluorescence of Fully Inorganic,Colloidal Gold Nanoclusters

Noble metal alloy nanoclusters (NCs) are interesting systems as the properties of two or more elements can be combined in one particle, leading to interesting fluorescence phenomena. However, previous studies have been exclusively performed on ligand-capped NCs from wet chemical synthesis. This makes it difficult to differentiate to which extent the fluorescence is affected by ligand-induced effects or the elemental composition of the metal core. In this work, we used laser fragmentation in liquids (LFL) to fabricate colloidal gold-rich bi-metallic AuPt NCs in the absence of organic ligands and demonstrate the suitability of this technique to produce molar fraction series of 1nm alloy NC. We found that photoluminescence of ligand-free NCs is not a phenomenon limited to Au. However, even minute amounts of Pt atoms in the AuPt NCs lead to quenching and red-shift of the fluorescence, which may be attributed to the altered surface charge density.     

Characterization of individual atmospheric particles by element mapping in electron probe microanalysis

In this paper procedures for the characterization of individual aerosol particles by element mapping in the electron microprobe are presented. The number, size and qualitative chemical composition of particles is derived from a combination of secondary or backscattered electron images and element distribution maps. Accuracy of the size distribution and reliability of the qualitative analysis procedure were checked with silicate samples. In order to obtain a semi-quantitative estimate of the chemical composition of individual particles the count rates taken from element distribution maps are corrected for matrix and geometric effects using particle ZAF procedures.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

A Molecular Photosensitizer in a Porous Block Copolymer Matrix-Implications for the Design of Photocatalytically Active Membranes

Recently, porous photocatalytically active block copolymer membranes were introduced, based on heterogenized molecular catalysts. Here, we report the integration of the photosensitizer, i. e., the light absorbing unit in an intermolecular photocatalytic system into block copolymer membranes in a covalent manner. We study the resulting structure and evaluate the orientational mobility of the photosensitizer as integral part of the photocatalytic system in such membranes. To this end we utilize transient absorption anisotropy, highlighting the temporal reorientation of the transition dipole moment probed in a femtosecond pump-probe experiment. Our findings indicate that the photosensitizer is rigidly bound to the polymer membrane and shows a large heterogeneity of absolute anisotropy values as a function of location probed within the matrix. This reflects the sample inhomogeneity arising from different protonation states of the photosensitizer and different intermolecular interactions of the photosensitizers within the block copolymer membrane scaffold.     

A Versatile Compact Parahydrogen Membrane Reactor

We introduce a Spin Transfer Automated Reactor (STAR) that produces continuous parahydrogen induced polarization (PHIP), which is stable for hours to days. We use the PHIP variant called signal amplification by reversible exchange (SABRE), which is particularly well suited to produce continuous hyperpolarization. The STAR is operated in conjunction with benchtop (1.1 T) and high field (9.4 T) NMR magnets, highlighting the versatility of this system to operate with any NMR or MRI system. The STAR uses semipermeable membranes to efficiently deliver parahydrogen into solutions at nano to milli Tesla fields, which enables ¹H, ¹³C, and ¹⁵N hyperpolarization on a large range of substrates including drugs and metabolites. The unique features of the STAR are leveraged for important applications, including continuous hyperpolarization of metabolites, desirable for examining steady-state metabolism in vivo, as well as for continuous RASER signals suitable for the investigation of new physics.     

Hydrogen Peroxide Detection Using Prussian Blue-modified 3D Pyrolytic Carbon Microelectrodes

A highly sensitive amperometric Prussian blue-based hydrogen peroxide sensor was developed using 3D pyrolytic carbon microelectrodes. A 3D printed multielectrode electrochemical cell enabled simultaneous highly reproducible Prussian blue modification on multiple carbon electrodes. The effect of oxygen plasma pre-treatment and deposition time on Prussian blue electrodeposition was studied. The amperometric response of 2D and 3D sensors to the addition of hydrogen peroxide in μM and sub-μM concentrations in phosphate buffer was investigated. A high sensitivity comparable to flow injection systems and a detection limit of 0.16 μM was demonstrated with 3D pyrolytic carbon microelectrodes at stirred batch condition     

Post-polymerization modification of aromatic polyimides via Diels-Alder cycloaddition

We report a facile post-polymerization modification route to functionalized aromatic polyimides via Diels-Alder cycloaddition. Aromatic polyimides are important, versatile high-performance polymers; however, their structural diversity is restricted by the requirements of the step-growth polymerization. We prepared polyimides with alkynes in their main-chain as macromolecular dienophiles and quantitatively grafted tetraphenylcyclopentadienone based dienes. The resulting solution-processable, wholly aromatic polyimides show a considerable increase in surface area due to the induced conformational changes and bulky, rigid, and contorted molecular structures. The orthogonality of the reaction is exploited to insert functional groups, namely bromine and sulfonates, along the polymer backbone. In a further extension, the phenylene segments undergo cyclodehydrogenation to form nanographene segments within the polymer chains. The Diels-Alder cycloaddition onto polyimides is therefore demonstrated to be an effective, widely applicable route to tunable high-performance polymers with value-added functionality and thus considerable potential in a wide range of advanced materials.