Photo-responsive chemical systems enabling multiscale structural ordering.

Despite their structural and functional differences, synthetic supramolecular assemblies share many similarities with biological assemblies, especially enzymes. The assemblies can be on the same length scale, and their structures and guest binding are typically governed by non-covalent interactions. Thus, only relatively weak interactions define the shape of a synthetic supramolecule or the secondary and tertiary structure of a protein, such that the resulting dynamism makes structure elucidation challenging. For biomolecules such as peptides, proteins, glycans and lipids this has often been tackled using ion mobility–mass spectrometry (IM-MS), whereby analyte ions are separated according to their gas-phase mobility and their mass-to-charge ratio. IM-MS is an established method in omics, separation sciences and small-molecule structural chemistry, but has only recently grown in popularity for the study of synthetic supramolecular assemblies in the gas phase. This Review describes IM-MS techniques and how they can help us understand the structures of molecular self-assemblies, host–guest complexes and metallosupramolecular complexes. Ion mobility–mass spectrometry (IM-MS) is a gas-phase method for structural characterization — a tool prevalent in biology but only recently finding applications in supramolecular chemistry. This Perspective describes how IM-MS techniques give us information about the structures of molecular self-assemblies, host–guest complexes and metallosupramolecular systems.

Regulation of Bi2O3 phase structure improves the self-powered UV-blue dual‐band photoresponse of Bi2O3/TiO2 photodetectors and the imaging application

Positron annihilation spectroscopy and micellar systems

The construction and investigation of photoresponsive and redox-active supramolecular systems with acetylenyl (polyyne) and cumulenic sp hybridized carbon chains (Cn) are reported here. Novel types of one-dimensional rigid molecular rods and macrocyclic molecular squares with controllable and yet fixed chain lengths or cavity sizes are explored. Such systems will have the desired features such as synthetic accessibility, coordination versatility, rigidity, directionality, photostability, electronic conductivity, controllable distances between donors and acceptors, and controllable cavity sizes in macrocyclic molecular squares. These features are extremely important to the future applications of these new rigid supramolecular systems in molecular photonic and electronic devices, light-energy conversion, molecular recognition, and host-guest chemistry. In addition to the exploration of synthetic features, the solution state redox characteristics and molecular photophysics of the metal-containing supramolecular systems with sp carbon chains are also under investigation. This includes the modulation of electronic communication between multiple redox centers spanned by rigid spacers of various chain lengths and the study of long-range, directional photoinduced energy/electron transfer across such spacers. In addition, covalent surface confinement of systems containing sp carbon chains is also investigated here. Specifically, UV/vis and X-ray photoelectron spectroscopy have been used as spectroscopic tools to monitor the growth of mono-and multilayer thin films.

In this research, the self-assembly behaviors of two different symmetry carboxylic acid derivatives (H3BTE and H4BTE) regulated by solvent and guest molecule (coronene, COR) were explored at the liquid/solid interface by scanning tunneling microscopy, and the formation mechanism was investigated by density functional theory. In 1-phenyloctane, only H3BTE molecules dissolved with extremely low concentration and self-assembled into a honeycomb structure and a new strip structure, while H4BTE could not. In 1-heptanoic acid, H3BTE and H4BTE were easily dissolved, in which H3BTE formed a regular row structure and H4BTE formed a tetragonal structure, respectively. The host-guest interaction was investigated by introducing the COR molecules into their self-assembly structures, and due to the different symmetry, H3BTE and H4BTE displayed different accommodation behavior.

A series of fully conjugated quinoxaline-based oligophenylene macrocycles is synthesized by Ni(0)-mediated Yamamoto-type diaryl homocoupling of (fluorinated) 2,3-bis(4'-bromophenyl)quinoxaline precursors. Cyclotrimers and cyclotetramers are obtained as the dominant reaction products. The cyclooligomers are fully characterized, including single-crystal X-ray structures, and their optoelectronic properties are analyzed with respect to possible applications in host-guest chemistry and organic electronics.

Self-assembled structural transition from vesicle phase to sponge phase and emulsifying properties in mixtures of arginine and fatty acids

The synthesis of BiAgOCh (Ch = S or Se) compounds has been successfully achieved via the ion exchange of copper with silver in aqueous solutions, starting from the copper parent phase. Optical and electrical measurements of BiAgOCh powders confirm an increase in both the bandgap and the electrical resistivity, as compared to those of the copper compounds. The structure of the BiAgOS phase has been clearly examined. X-ray diffraction synchrotron measurements coupled with advanced high-resolution transmission electron microscopy analysis evidenced a Ag-deficient structure, as well as Bi-rich defects, both types of defects being oppositively charged. Silver atoms are also found in interstial sites, which explains the two-dimensional ionic conductivity. This structural study combined with theoretical calculations explains the intrinsic conductivity behavior of these semiconductors linked to the mutual compensation of both defect types in the structure and to the increase in the hole effective mass. This study shows the feasibility of modifying the optoelectronic properties of the BiMOCh compounds, with the goal of integrating them in heterojunction solar cells. Moreover, it provides very precise insight into the complexity of the relationship between structural defects and optoelectronic properties.

Strained epitaxy has been shown to produce pyramidal-shaped semiconductor dot structures by single-step epitaxy. The very high density of these dots (approaching per wafer) and their ever improving uniformity suggest that these features could have important applications in future microelectronics. Understanding the structural and electronic properties of these quantum dots is therefore of great importance. In this paper, we examine some of the physics controlling the performance of devices that could be made from such structures. The self-assembled quantum dots are highly strained and we will examine the strain tensor in these quantum dots using a valence force-field model. In this paper we will address the following issues: (1) What is the general nature of the strain tensor in self assembled quantum dots? (2) What are the electron and hole spectra for InAs-GaAs quantum dots? (a) What are the important intersubband radiative and nonradiative scattering processes in the self assembled quantum dots? In particular, we will discuss how the electron-phonon interactions are modified in the quantum dot structures. Consequences for uncooled intersubband devices such as lasers, detectors, and quantum transistors will be briefly discussed.

Polydiacetylenes are well-established one-dimensional organic semiconductors that have been generated by photochemical and thermal polymerizations of diacetylenes in single crystals, gel phases, thin films, and membranes. Their formation in mesophases, such as liquid crystals, has been surprisingly little studied although higher-ordered mesophases should support the topochemical polymerization of diacetylenes (1,3-butadiyne groups) and may give access to large domains of uniformly aligned materials. The polymerization of diacetylenes in a mesophase may also increase the stability of the self-assembled supramolecular structure. Here, the dye and discotic mesogen tetraazaporphyrin was decorated with eight diacetylene-containing alkyl chains to probe its mesomorphism and conversion into multifunctional polydiacetylene materials. While the incorporation of diacetylene groups supports columnar mesomorphism, successful photopolymerization required the presence of directing amide groups that suppressed columnar in favor of nematic mesomorphism. Still, the polymerization of the nematic mesophase generated a soluble nematic polydiacetylene of significantly higher molecular weight (Mn = 77 kDa or 25 monomer units by gel permeation chromatography) than what has been obtained in gel phases of related compounds. The formation of polydiacetylene was confirmed by Raman spectroscopy, and its nematic structure was verified by UV-vis spectroscopy, polarized optical microscopy, and X-ray diffraction. Both its nematic structure and the incorporation of eight side chains per discotic unit provide the polydiacetylene with sufficient solubility for casting thin films on substrates. Atomic force microscopy studies of films on silicon wafers revealed a grid-like structure of connected nanofibers. This study demonstrates the requirements for the formation of multifunctional mesomorphic polydiacetylene materials from mesomorphic precursors and their advantages. Optimization of the presented molecular design should give access to other mesophases and, consequently, functional polydiacetylene materials with tunable structures and optoelectronic properties.

Hydrophilic host-guest complexes, consisting of water-soluble azobenzene and α-, β-, or γ-cyclodextrins, have been proposed as a model to study supramolecular photoresponsive systems in aqueous environments through a full spectrometric approach combined with a simulation and data fitting methodology. Various essential and complementary spectroscopic techniques have been used: circular dichroism to determine whether the complex is formed or not, NMR for the stoichiometry elucidation, and UV-visible spectrophotometry to obtain the association equilibrium constant of each complex and the quantum yield for each photochemical process. A step-by-step fitting procedure is presented, which enables the determination of all thermodynamic and photokinetic parameters. A sequential methodology is applied to dissipate all uncertainties on the variability of the results and to develop a relevant and reliable protocol applicable to other types of complexes. The proposed procedure has thus been shown to be very robust and largely applicable to other photoresponsive host-guest systems.

In this laboratory experiment, students follow a step-by-step procedure to prepare and study guest–host complexes in the gas phase using electrospray ionization–mass spectrometry (ESI–MS). Model systems are the complexes of hosts cucurbit[7]uril (CB7) and cucurbit[8]uril (CB8) with the guest 4-styrylpyridine (SP). Aqueous solutions of CB7 or CB8 with SP are infused, and full scan spectra are obtained. Students analyze the ESI–MS full scan signals and discuss the structure of the guest–host complexes based on the monoisotopic masses of hosts and guest and observed m/z values on the charge states and on the experimental and simulated isotope distributions. Complexes are fragmented, and spectra were obtained. The assignments are further examined taking into account the fragmentation data. The structure and gas phase reactivity of the identified supramolecular associations are discussed in view of the fragmentation patterns and host size.

Magnesium alloys are extensively utilized in aerospace, aviation, and automotive sectors due to their low density and high specific strength, which offer significant advantages for lightweight structural applications. Their low density especially directs the attention of the aviation sector, where lightness is necessary, to these alloys. However, one of the disadvantages that restricts their use in the industry is their low corrosion resistance. In this study, the Plasma Electrolytic Oxidation (PEO) process was applied in a silicate-based electrolyte to AZ61 magnesium alloy pre-coated with aluminum using the electric arc spraying technique. To examine the characteristics of the fabricated coatings, their phase structures, surface features, and elemental compositions were investigated through XRD, SEM, and EDS analyses. Corrosion performances of coatings were investigated by potentiodynamic polarization test in 3.5% NaCl solution. As a result of electrochemical tests, corrosion current density values for the base sample (AZ61) and PEO coating (AZ61-PEO) were determined as 36,29〖 μA.cm〗^(-2) and 6,53〖 μA.cm〗^(-2), respectively. The findings highlight that the Al₂O₃ layer formed following PEO treatment significantly enhanced the corrosion resistance compared to the base sample.

Experimental studies on photocatalytic reduction of CO2 using AgBr decorated g-C3N4 composite in TEA mediated system

Corrosion behavior of ZrO2-TiO2 composite coatings produced on titanium alloy via plasma electrolytic oxidation