Abstract
Supported atomic metal sites have discrete molecular orbitals. Precise control over the energies of these sites is key to achieving novel reaction pathways with superior selectivity. Here, ...we achieve selective oxygen (O
2
) activation by utilising a framework of cerium (Ce) cations to reduce the energy of 3
d
orbitals of isolated copper (Cu) sites. Operando X-ray absorption spectroscopy, electron paramagnetic resonance and density-functional theory simulations are used to demonstrate that a Cu(I)O
2
3−
site selectively adsorbs molecular O
2
, forming a rarely reported electrophilic η
2
-O
2
species at 298 K. Assisted by neighbouring Ce(III) cations, η
2
-O
2
is finally reduced to two O
2−
, that create two Cu–O–Ce oxo-bridges at 453 K. The isolated Cu(I)/(II) sites are ten times more active in CO oxidation than CuO clusters, showing a turnover frequency of 0.028 ± 0.003 s
−1
at 373 K and 0.01 bar
P
CO
. The unique electronic structure of Cu(I)O
2
3−
site suggests its potential in selective oxidation.
One of the most prominent hole‐transporting material (HTM) for hybrid perovskite solar cells has been 2,2″,7,7″‐tetrakisN,N‐di(4‐methoxyphenyl)amino‐9,9′‐spirobifluorene (spiro‐OMeTAD), which is ...commonly doped with metal bis(trifluoromethylsulfonyl)imide (M(TFSI)n) salts that contribute to generating the active radical cation HTM species. The underlying role of the metal cation, however, remains elusive. Here, the effect of metal cations (M = Li, Zn, Ca, Cu, and Sc) on doping spiro‐OMeTAD is analyzed by a combination of techniques, including electron paramagnetic resonance spectroscopy and cyclic voltammetry, which is complemented by photovoltaic device and hole mobility analysis. As a result, the authors reveal the superiority of Zn(TFSI)2 salts in device performances as compared to the others, including redox‐active Cu(TFSI)2. This analysis thereby unravels new design principles for dopant engineering in HTMs for hybrid perovskite photovoltaics.
Dopant engineering for spiro‐OMeTAD hole‐transporting materials towards efficient perovskite solar cells. The presence of M(TFSI)n salts as p‐type dopants are required to improve the hole transfer of spiro‐OMeTAD, critical for photovoltaic performance. This study assesses the role of metal cations in the process, revealing the superiority of Zn‐based dopants as compared to redox‐active Cu‐based ones and others as producing a very high fill factor of close to 80% a VOC of 1.15 V and a power conversion efficiency of 21.9%.
We present the synthesis and characterization of enantiomerically pure 6helicene o-quinones (P)-(+)-1 and (M)-(−)-1 and their application to chiroptical switching and chiral recognition. (P)-(+)-1 ...and (M)-(−)-1 each show a reversible one-electron reduction process in their cyclic voltammogram, which leads to the formation of the semiquinone radical anions (P)-(+)-1 •– and (M)-(−)-1 •–, respectively. Spectroelectrochemical ECD measurements give evidence of the reversible switching between the two redox states, which is associated with large differences of the Cotton effects Δ(Δε) in the UV and visible regions. The reduction of (±)-1 by lithium metal provides Li+{(±)-1 •–}, which was studied by EPR and ENDOR spectroscopy to reveal substantial delocalization of the spin density over the helicene backbone. DFT calculations demonstrate that the lithium hyperfine coupling A(7Li) in Li+{(±)-1 •–} is very sensitive to the position of the lithium cation. On the basis of this observation, chiral recognition by ENDOR spectroscopy was achieved by complexation of Li+{(P)-(+)-1 •–} and Li+{(M)-(−)-1 •–} with an enantiomerically pure phosphine oxide ligand.
The anti (
a
) to syn (
s
) isomerization pathway of the deprotonated form of the dimer with two nickel(II) 15-membered octaazamacrocyclic units connected via a carbon–carbon (C–C) σ bond was ...investigated. For the initial anti (
a
) structure, a deprotonation of one of the bridging (
sp
3
hybridized) carbon atoms is suggested to allow for an
a
to
s
geometry twist. A 360° scan around the bridging C–C dihedral angle was performed first to find an intermediate geometry. Subsequently, the isomerization pathway was explored via individual steps using a series of mode redundant geometry optimizations (internal coordinates potential energy surface scans) and geometry relaxations leading to the
s
structure. The prominent geometries (intermediates) of the isomerization pathway are chosen and compared to the
a
and
s
structures, and geometry relaxations of the protonated forms of selected intermediates are considered.
Star‐shaped polymers represent highly desired materials in nanotechnology and life sciences, including biomedical applications (e.g., diagnostic imaging, tissue engineering, and targeted drug ...delivery). Herein, we report a straightforward synthesis of wavelength‐selective multifunctional photoinitiators (PIs) that contain a bisacylphosphane oxide (BAPO) group and an α‐hydroxy ketone moiety within one molecule. By using three different wavelengths, these photoactive groups can be selectively addressed and activated, thereby allowing the synthesis of ABC‐type miktoarm star polymers through a simple, highly selective, and robust free‐radical polymerization method. The photochemistry of these new initiators and the feasibility of this concept were investigated in unprecedented detail by using various spectroscopic techniques.
Waiting for the perfect wave: Wavelength‐selective multifunctional photoinitiators (PIs) enable the preparation of ABC‐type miktoarm star polymers through a simple, selective, and robust free‐radical polymerization method.
Two 15-membered octaazamacrocyclic nickel(II) complexes are investigated by theoretical methods to shed light on their affinity forwards binding and reducing CO2. In the first complex 1NiIIL0, the ...octaazamacrocyclic ligand is grossly unsaturated (π-conjugated), while in the second 1NiIILH2+ one, the macrocycle is saturated with hydrogens. One and two-electron reductions are described using Mulliken population analysis, quantum theory of atoms in molecules, localized orbitals, and domain averaged fermi holes, including the characterization of the Ni-CCO2 bond and the oxidation state of the central Ni atom. It was found that in the NiLH complex, the central atom is reduced to Ni0 and/or NiI and is thus able to bind CO2 via a single σ bond. In addition, the two-electron reduced 3NiL2− species also shows an affinity forwards CO2.
A variety of asymmetrically donor–acceptor‐substituted 3cumulenes (buta‐1,2,3‐trienes) were synthesized by developed procedures. The activation barriers to rotation ΔG≠ were measured by variable ...temperature NMR spectroscopy and found to be as low as 11.8 kcal mol−1, in the range of the barriers for rotation around sterically hindered single bonds. The central CC bond of the push–pull‐substituted 3cumulene moiety is shortened down to 1.22 Å as measured by X‐ray crystallography, leading to a substantial bond length alternation (BLA) of up to 0.17 Å. All the experimental results are supported by DFT calculations. Zwitterionic transition states (TS) of bond rotation confirm the postulated proacetylenic character of donor–acceptor 3cumulenes. Additional support for the proacetylenic character of these chromophores is provided by their reaction with tetracyanoethene (TCNE) in a cycloaddition‐retroelectrocyclization (CA–RE) cascade characteristic of donor‐polarized acetylenes.
A series of push–pull‐substituted 3cumulenes was synthesized. Extensive UV/Vis, X‐ray, VT NMR, and computational studies confirmed their proacetylenic character. The measured rotational barriers of the new cumulenes are in the range of those of sterically crowded single bonds and reach values down to ΔG≠=11.8 kcal mol−1. The proacetylenic reactivity of the central CC double bond was proven by the facile, high‐yielding cycloaddition‐retroelectrocyclization reaction with tetracyanoethene at room temperature yielding stable zwitterions.
Cobalt complexes with multiproton- and multielectron-responsive ligands are of interest for challenging catalytic transformations. The chemical and redox noninnocence of pentane-2,4-dione ...bis(S-methylisothiosemicarbazone) (PBIT) in a series of cobalt complexes has been studied by a range of methods, including spectroscopy UV–vis, NMR, electron paramagnetic resonance (EPR), X-ray absorption spectroscopy (XAS), cyclic voltammetry, X-ray diffraction, and density functional theory (DFT) calculations. Two complexes CoIII(H2LSMe)II and CoIII(LSMe )I2 were found to act as precatalysts in a Wacker-type oxidation of olefins using phenylsilane, the role of which was elucidated through isotopic labeling. Insights into the mechanism of the catalytic transformation as well as the substrate scope of this selective reaction are described, and the essential role of phenylsilane and the noninnocence of PBIT are disclosed. Among the several relevant species characterized was an unprecedented Co(III) complex with a dianionic diradical PBIT ligand (CoIII(LSMe••)I).
The stability of hybrid organic–inorganic halide perovskite semiconductors remains a significant obstacle to their application in photovoltaics. To this end, the use of low‐dimensional (LD) ...perovskites, which incorporate hydrophobic organic moieties, provides an effective strategy to improve their stability, yet often at the expense of their performance. To address this limitation, supramolecular engineering of noncovalent interactions between organic and inorganic components has shown potential by relying on hydrogen bonding and conventional van der Waals interactions. Here, the capacity to access novel LD perovskite structures that uniquely assemble through unorthodox S‐mediated interactions is explored by incorporating benzothiadiazole‐based moieties. The formation of S‐mediated LD structures is demonstrated, including one‐dimensional (1D) and layered two‐dimensional (2D) perovskite phases assembled via chalcogen bonding and S–π interactions. This involved a combination of techniques, such as single crystal and thin film X‐ray diffraction, as well as solid‐state NMR spectroscopy, complemented by molecular dynamics simulations, density functional theory calculations, and optoelectronic characterization, revealing superior conductivities of S‐mediated LD perovskites. The resulting materials are applied in n‐i‐p and p‐i‐n perovskite solar cells, demonstrating enhancements in performance and operational stability that reveal a versatile supramolecular strategy in photovoltaics.
A new generation of low‐dimensional hybrid halide perovskite materials assembled via chalcogen bonding and S–π interactions is demonstrated by a combination of techniques, including X‐ray diffraction and solid‐state nuclear magnetic resonance spectroscopy, complemented by molecular dynamics simulations, density functional theory calculations, and optoelectronic characterization, revealing superior conductivities and enhancements in performance and operational stabilities in perovskite solar cells.
The antioxidant properties of 15 honey samples from different floral sources and various Slovak regions were investigated by means of electron paramagnetic resonance spectroscopy. Cation radical of ...ABTS (2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) diammonium salt), DPPH (1,1-diphenyl-2-picrylhydrazyl) and hydroxyl radicals generated by the photochemical decomposition of hydrogen peroxide were used as oxidants. The antioxidant activities found with ABTS+, expressed as trolox equivalent antioxidant capacity (TEAC), ranged from 0.15 to 1.14mmolkg−1, and those determined with DPPH, from 0.04 to 0.32mmolkg−1. TEAC values correlated well with results found by elimination of DPPH, and both values revealed a linear relationship with the concentration of phenolics obtained with the Folin–Ciocalteu phenol test (expressed as gallic acid equivalents, GAE). The colour coordinates (CIE L∗a∗b∗), as well as reflectance spectra determined for original honeys using a white background, demonstrated that the colour difference (ΔE∗) and coordinate b∗ interrelate with TEAC values. The radical-scavenging capacities (RSC) of the honey samples determined in the experiments with photochemically decomposed hydrogen peroxide, generating reactive OH radicals in the presence of spin trapping agent, differ from those found with ABTS+ and DPPH. Here, probably, the reactive OH radicals, having higher redox potential, are scavenged by a variety of compounds not effective with ABTS+ and DPPH (e.g., saccharides, proteins).
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