2D halide perovskite‐like semiconductors are attractive materials for various optoelectronic applications, from photovoltaics to lasing. To date, the most studied families of such low‐dimensional halide perovskite‐like compounds are Ruddlesden–Popper, Dion–Jacobson, and other phases that can be derived from 3D halide perovskites by slicing along different crystallographic directions, which leads to the spatially isotropic corner‐sharing connectivity type of metal‐halide octahedra in the 2D layer plane. In this work, a new family of hybrid organic–inorganic 2D lead halides is introduced, by reporting the first example of the hybrid organic–inorganic post‐perovskite 3‐cyanopyridinium lead tribromide (3cp)PbBr3. The post‐perovskite structure has unique octahedra connectivity type in the layer plane: a typical “perovskite‐like” corner‐sharing connectivity pattern in one direction, and the rare edge‐sharing connectivity pattern in the other. Such connectivity leads to significant anisotropy in the material properties within the inorganic layer plane. Moreover, the dense organic cation packing results in the formation of 1D fully organic bands in the electronic structure, offering the prospects of the involvement of the organic subsystem into material's optoelectronic properties. The (3cp)PbBr3 clearly shows the 2D quantum size effect with a bandgap around 3.2 eV and typical broadband self‐trapped excitonic photoluminescence at temperatures below 200 K.
The reduction of TiO 2 nanoparticle through interaction with H atom and characterization of resulting defect species with O 2 molecule adsorption were investigated by DFT calculations in a molecular cluster approach. The isolated cluster Ti 8 O 16 was used as a nanoparticle model. It was found that interaction between atomic hydrogen and every oxygen atom in Ti 8 O 16 has the following features: (1) formation of stable OH group, (2) low activation energy of the process, and (3) appearance of reduced Ti 3+ ion together with one corresponding d-type singly occupied level in the cluster's "band gap". Molecular hydrogen, in contrast with its atomic form, weakly interacts only with Ti atoms. Simulation of O 2 adsorption on each Ti 3+ ion of reduced Ti 8 O 16 H clusters shows the following: (1) formation of stable molecular O 2 − species, (2) the process has no any energetic barrier, and (3) disappearance of Ti 3+ defect center and corresponding d-type singly occupied level. The obtained results agree well with general experimental regularities of both H plasma TiO 2 reduction and interaction of reduced TiO 2 with oxygen. Specifically, calculations of g-tensor provide plausible quantitative description of Ti 3+ and O 2 − paramagnetic species. Consistently the computational approach under consideration can be therefore applied to local surfaces phenomena associated with nanoscaled TiO 2 .
Density functional theory calculations for neutral and oxidized diferrocenyldiphenylcumulenes, [Fc(Ph)C n (Ph)Fc] with n ) 2, 4, 6, 8, were performed at the B3LYP/6-31G level without any restrictions in symmetry. Geometrically, of the four possible diasteromeric structures of the neutral cumulenes, no preferential conformation was revealed, and the calculated structures reproduce the experimental X-ray structural data quite well. The spin density of all mono-and dications is located on the iron atoms, but not on the cumulene chain. Calculations of the ionization potentials for monocations show a breakdown of Koopmans' theorem. A calibration procedure was proposed for evaluation of vertical ionization potentials, resulting in values with experimental accuracy. UV-visible absorptions are assigned in terms of their band maximums, transition energies, and bandwidths on the basis of deconvoluted experimental spectra and on the basis of comparison with structurally related compounds. Calculations of the characteristic high-frequency symmetric vibrations of the cumulene chain show a very good match with experimental Raman bands. Redox potentials in solution are calculated by a simplified model on the basis of empirical findings; the results reproduce the experimental half-wave potentials quite satisfactorily and allow an estimate of an electrochemical decay slope and an effective conjugation limit in these cumulene molecular wires. The structural, chemical, optical, electrochemical, and molecular orbital properties of 2-31 make ferrocenyl cumulenes very promising molecular objects with great potential in molecular-scale electronics in comparison with pure organic molecular wires.
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