: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Further enhancing the performance and stability of inverted perovskite solar cells (PSCs) is crucial for their commercialization. We report that the functionalization of multication and halide perovskite interfaces with an organometallic compound, ferrocenyl-bis-thiophene-2-carboxylate (FcTc2), simultaneously enhanced the efficiency and stability of inverted PSCs. The resultant devices achieved a power conversion efficiency of 25.0% and maintained >98% of their initial efficiency after continuously operating at the maximum power point for 1500 hours under simulated AM1.5 illumination. Moreover, the FcTc2-functionalized devices passed the international standards for mature photovoltaics (IEC61215:2016) and have exhibited high stability under the damp heat test (85°C and 85% relative humidity). Description Organometallics stabilizing perovskites Perovskite solar cells with inverted (p-i-n) structure can have greater stability and lifetimes than conventional n-i-p structures but usually have somewhat lower power conversion efficiencies (PCEs). Li et al. report that an organometallic compound, ferrocenyl-bis-thiophene-2-carboxylate, can stabilize a multication perovskite layer of an inverted perovskite solar cells. After 1500 hours of maximum power point operation, 98% of the 25.0% PCE was maintained. The solar cell also exhibited high stability in damp heat tests. —PDS Functionalizing interfaces with an organometallic compound created an efficient and stable inverted perovskite solar cell.

Organometallic-functionalized interfaces for highly efficient inverted perovskite solar cells

A critical review of the state-of-the-art evidence in support of the mechanisms of glycosylation reactions is provided. Factors affecting the stability of putative oxocarbenium ions as intermediates at the SN1 end of the mechanistic continuum are first surveyed before the evidence, spectroscopic and indirect, for the existence of such species on the time scale of glycosylation reactions is presented. Current models for diastereoselectivity in nucleophilic attack on oxocarbenium ions are then described. Evidence in support of the intermediacy of activated covalent glycosyl donors is reviewed, before the influences of the structure of the nucleophile, of the solvent, of temperature, and of donor–acceptor hydrogen bonding on the mechanism of glycosylation reactions are surveyed. Studies on the kinetics of glycosylation reactions and the use of kinetic isotope effects for the determination of transition-state structure are presented, before computational models are finally surveyed. The review concludes with ...

/pdf/the-experimental-evidence-in-support-of-glycosylation-qm4cq0in86.pdf

The Experimental Evidence in Support of Glycosylation Mechanisms at the SN1–SN2 Interface

Methods for site-selective transformations of hydroxyl groups in carbohydrate derivatives are reviewed. The construction of oligosaccharides of defined connectivity hinges on such transformations, which are also needed for the preparation of modified or non-natural sugar derivatives, the installation of naturally occurring postglycosylation modifications, the selective labeling or conjugation of carbohydrate derivatives, and the preparation of therapeutic agents or research tools for glycobiology. The review begins with a discussion of intrinsic factors and processes that can influence selectivity in reactions of unprotected or partially protected carbohydrate derivatives, followed by a description of transformations that engage two OH groups in cyclic adducts (acetals, ketals, boronic esters, and related species). An overview of the various classes of site-selective transformations of OH groups in sugars is then provided: the reactions discussed include esterification, thiocarbonylation, alkylation, glycosylation, arylation, silylation, phosphorylation, sulfonylation, sulfation, and oxidation. Emphasis is placed on recently developed methods that employ reagent or catalyst control to achieve otherwise challenging transformations or site-selectivities.

Site-Selective Functionalization of Hydroxyl Groups in Carbohydrate Derivatives.

Half-Wave Potential Splittings ΔE1/2 as a Measure of Electronic Coupling in Mixed-Valent Systems: Triumphs and Defeats

Regio- and stereoselective insertion of the terminal ethynyl functions of 4-ethynylstilbene, the E and Z isomers of 4,4′-bis(ethynylphenyl)ethene and a backbone-rigidified cyclohexenyl derivative of the Z isomer into the Ru–H bond of the complex RuClH(CO)(PiPr3)2 provides the corresponding vinyl ruthenium complexes, which have been characterized spectroscopically and by X-ray crystallography. Large red shifts of the UV/vis absorption bands evidence efficient incorporation of the vinyl metal subunit(s) into the conjugated π-system. All complexes oxidize at low potentials. The various oxidized forms of all complexes were generated and characterized by UV/vis/NIR, IR and EPR spectroscopies. These studies indicated electrocatalytic Z→E isomerization of the oxidized Z-distyrylethene complex Ru-Z2, which is prevented in its backbone-rigidified derivative Ru-Z2fix. The radical cations of the E and the configurationally stable cyclohexene-bridged Z-derivatives are spin-delocalized on the EPR time scale but charge...

/pdf/ruthenium-stilbenyl-and-diruthenium-distyrylethene-complexes-hkqhj6ber3.pdf

Ruthenium stilbenyl and diruthenium distyrylethene complexes: aspects of electron delocalization and electrocatalyzed isomerization of the Z-isomer.

Cyclic molecules often exhibit unusual properties; consider for example the resonance stabilization energy of benzene or the strong cation binding of crown ethers. Now, a family of rings comprising varying numbers of directly linked ferrocenes has been prepared. These compounds are highly symmetric in solution and undergo rapid ‘oxidation-state isomerism’ when charged.

Oligomeric ferrocene rings

Trinuclear ferrocene tris-amides were synthesized from an Fmoc- or Boc-protected ferrocene amino acid, and hydrogen-bonded zigzag conformations were determined by NMR spectroscopy, molecular modelling, and X-ray diffraction. In these ordered secondary structures orientation of the individual amide dipole moments approximately in the same direction results in a macrodipole moment similar to that of α-helices composed of α-amino acids. Unlike ordinary α-amino acids, the building blocks in these ferrocene amides with defined secondary structure can be sequentially oxidized to mono-, di-, and trications. Singly and doubly charged mixed-valent cations were probed experimentally by Vis/NIR, paramagnetic ¹H NMR and Mossbauer spectroscopy and investigated theoretically by DFT calculations. According to the appearance of intervalence charge transfer (IVCT) bands in solution, the ferrocene/ferrocenium amides are described as Robin-Day class II mixed-valent systems. Mossbauer spectroscopy indicates trapped valences in the solid state. The secondary structure of trinuclear ferrocene tris-amides remains intact (coiled form) upon oxidation to mono- and dications according to DFT calculations, while oxidation to the trication should break the intramolecular hydrogen bonding and unfold the ferrocene peptide (uncoiled form).

Michael Linseis

Papers

Ruthenium stilbenyl and diruthenium distyrylethene complexes: aspects of electron delocalization and electrocatalyzed isomerization of the Z-isomer.

Oligomeric ferrocene rings

Oligonuclear ferrocene amides: mixed-valent peptides and potential redox-switchable foldamers.

Vinyl-ruthenium entities as markers for intramolecular electron transfer processes

Divinylphenylene- and Ethynylvinylphenylene-Bridged Mono-, Di-, and Triruthenium Complexes for Covalent Binding to Gold Electrodes