The bottom-up assembly of nanoparticles into diverse ordered solids is a challenge because it requires nanoparticles, which are often quasi-spherical, to have interaction anisotropy akin to atoms and molecules. Typically, anisotropy has been introduced by changing the shape of the inorganic nanoparticle core. Here, we present the design, self-assembly, optical properties, and total structural determination of Ag29(BDT)12(TPP)4, an atomically precise tetravalent nanocluster (NC) (BDT, 1,3-benzenedithiol; TPP, triphenylphosphine). It features four unique tetrahedrally symmetrical binding surface sites facilitated by the supramolecular assembly of 12 BDT (wide footprint bidentate thiols) in the ligand shell. When each of these sites was selectively functionalized by a single phosphine ligand, particle stability, synthetic yield, and the propensity to self-assemble into macroscopic crystals increased. The solid crystallized NCs have a substantially narrowed optical band gap compared to that of the solution state, suggesting strong interparticle electronic coupling occurs in the solid state.

Distinct photocatalytic performance was observed when Ta 3 N 5 was synthesized from commercially available Ta 2 O 5 or from Ta 2 O 5 prepared from TaCl 5 via the sol−gel route. With respect to photocatalytic O 2 evolution with Ag + as a sacrificial reagent, the Ta 3 N 5 produced from commercial Ta 2 O 5 exhibited higher activity than the Ta 3 N 5 produced via the sol−gel route. When the Ta 3 N 5 photocatalysts were decorated with Pt nanoparticles in a similar manner, the Ta 3 N 5 from the sol−gel route exhibited higher photocatalytic hydrogen evolution activity from a 10% aqueous methanol solution than Ta 3 N 5 prepared from commercial Ta 2 O 5 where no hydrogen can be detected. Detailed surface and bulk characterizations were conducted to obtain fundamental insight into the resulting photocatalytic activities. The characterization techniques, including XRD, elemental analysis, Raman spectroscopy, UV−vis spectroscopy, and surface-area measurements, revealed only negligible differences between these two photocatalysts. Our thorough characterization of the surface properties demonstrated that the very thin outermost layer of Ta 3 N 5 , with a thickness of a few nanometers, consists of either the reduced state of tantalum (TaN) or an amorphous phase. The extent of this surface layer was likely dependent on the nature of precursor oxide surfaces. DFT calculations based on partially oxidized Ta 3 N 4.83 O 0.17 and N deficient Ta 3 N 4.83 consisting of reduced Ta species well described the optoelectrochemical properties obtained from the experiments. Electrochemical and Mott−Schottky analyses demonstrated that the surface layer drastically affects the energetic picture at the semiconductor−electrolyte interface, which can consequently affect the photocatalytic performance. Chemical etching of the surface of Ta 3 N 5 particles to remove this surface layer unites the photocatalytic properties with the photocatalytic performance of these two materials. Mott−Schottky plots of these chemically etched Ta 3 N 5 materials exhibited similar characteristics. This result suggests that the surface layer (1−2 nm) determines the electrochemical interface, which explains the different photocatalytic performances of these two materials.

A lead-free and air-stable organohalide semiconductor exhibiting noteworthy optoelectronic properties is investigated. With improvements in thin film processing, this material is expected to yield good solar cell efficiency.

No abstract

Chemical bath deposition (CBD) of tin oxide (SnO) thin films as an electron-transport layer (ETL) in a planar-heterojunction n-i-p organohalide lead perovskite and organic bulk-heterojunction (BHJ) solar cells is reported. The amorphous SnO (a-SnO) films are grown from a nontoxic aqueous bath of tin chloride at a very low temperature (55 °C) and do not require postannealing treatment to work very effectively as an ETL in a planar-heterojunction n-i-p organohalide lead perovskite or organic BHJ solar cells, in lieu of the commonly used ETL materials titanium oxide (TiO) and zinc oxide (ZnO), respectively. Ultraviolet photoelectron spectroscopy measurements on the glass/indium-tin oxide (ITO)/SnO/methylammonium lead iodide (MAPbI)/2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene device stack indicate that extraction of photogenerated electrons is facilitated by a perfect alignment of the conduction bands at the SnO/MAPbI interface, while the deep valence band of SnO ensures strong hole-blocking properties. Despite exhibiting very low electron mobility, the excellent interfacial energetics combined with high transparency (E > 4 eV) and uniform substrate coverage make the a-SnO ETL prepared by CBD an excellent candidate for the potentially low-cost and large-scale fabrication of organohalide lead perovskite and organic photovoltaics.

a b s t r a c tPresented herein is a detailed discussion of the properties of the lattice dynamic and optoelectronic properties of tantalum(V) oxynitride (TaON) and tantalum(V) nitride (Ta 3 N 5 ), from experimental and theoretical standpoint. The active Raman and infra red (IR) frequencies of TaON and Ta 3 N 5 were measured using confocal Raman and Fourier Transform Infrared spectroscopies (FTIR) and calculated using the linear response method within the density functional perturbation theory (DFPT). The detailed study leads to an exhaustive description of the spectra, including the symmetry of the vibrational modes. Electronic structures of these materials were computed using DFT within the range-separated hybrid HSE06 exchange-correlation formalism. Electronic and ionic contributions to the dielectric constant tensors of these materials were obtained from DFPT within the linear response method using the PBE functional. Furthermore, effective mass of photogenerated holes and electrons at the band edges of these compounds were computed from the electronic band structure obtained at the DFT/HSE06 level of theory. The results suggest that anisotropic nature in TaON and Ta 3 N 5 is present in terms of dielectric constant and effective masses.

We have compared the photodynamic activities of hematoporphyrin (HP) and protoporphyrin (PP) on isolated rat liver mitochondria by measuring the decline of the respiratory control ratio (RCR) after irradiation at 365 nm. Before addition to the respiratory medium, the dyes were dissolved in phosphate-buffered saline (PBS) or incorporated into unilamellar liposomes of dipalmitoyl-phosphatidylcholine (DPPC), sometimes enriched with cholesterol (Chol) or cardiolipin (Card), which are naturally present in mitochondrial membranes. Chol and especially Card strongly increase the porphyrin uptake by mitochondria. In all experimental conditions, PP is taken up by mitochondria to a higher extent than HP. Nevertheless, under conditions giving the same amount of mitochondria-bound dye, HP is a more efficient photosensitizer than PP. As the efficiency of singlet oxygen production has been shown to be equivalent for the two porphyrins in monomeric state, the resulting photobiological effects are explained in terms of different localization of HP and PP in the mitochondrial membranes. In particular, HP preferentially localizes in the protein-rich polar domains of the inner mitochondrial membrane, whereas PP dissolves in the lipid regions of the membranes.

No abstract