Preparation and Reactions of Dichlorodithienogermoles

The reaction of 3,3′-dilithiobithiophenes with tetrachlorogermane afforded 4,4-dichlorodithienogermoles, which readily underwent substitution on the central germanium atom. Reactions of a dichlorodithienogermole with LiAlH₄, MeLi, Me₂NC₆H₄Li, and C₆F₅MgBr gave the corresponding Ge-substituted products. Dihydrodithienogermole obtained from the reaction with LiAlH₄ was further treated with LDA to give a dimer whose structure was verified by a single-crystal X-ray diffraction (XRD) study. Hydrolysis of dichlorodithienogermoles provided cyclotetragermoxanes. Their optical properties were examined with respect to the UV absorption and fluorescence spectra. It was found that one of the cyclotetragermoxanes responded to a nitorobenzene vapor in the solid state, decreasing the PL intensity

Phase Transition of <i>n</i>‑C₃₆H₇₄ Monolayer on Pt(111) Covered with Monolayer Graphene Studied by C K‑NEXAFS

The temperature-induced phase transition of the <i>n</i>-C₃₆H₇₄ monolayer on the monolayer graphene grown on a Pt(111) surface is studied by X-ray absorption fine structure spectroscopy in the carbon near the K-edge (C K-NEXAFS). The C K-NEXAFS spectra of the <i>n</i>-C₃₆H₇₄ monolayer is separated from the spectra of the monolayer graphene by subtraction. The σ_CC^* resonance predominantly observed in the normal incidence (NI) spectra is consistent with a chain axis lying flat on the graphene sheet at 120 K (crystalline phase) and 300 K (smectic phase). The σ_CH^*/R resonance at 287.2 eV is characteristic of the monolayer, which is attributed to the σ_CH^* orbitals distributed in an open space above the monolayer. The intensity ratio of the resonance for grazing incidence (GI) spectra with respect to that for normal incidence (NI) spectra decreases as a function of the temperature, which reflects the orientation change of the carbon plane with respect to the graphene sheet, from perpendicular (edge-on) to parallel (flat-on) orientation upon the crystalline–smectic transition, and the expansion of the intermolecular spacings upon further transition to the fluid phase at 400 K

Solid-State Near-Infrared Emission of π‑Conjugated Polymers Consisting of Boron Complexes with Vertically Projected Steric Substituents

The development of solid-state near-infrared (NIR)-emissive π-conjugated polymers (CPs) has been still difficult due to lack of valid guidelines for avoiding aggregation-caused quenching. To obtain solid-state emission, we designed new strong electron acceptors by employing boron-fused azobenzene complexes with vertically projected bulky substituents at boron, which can prevent the π-surface from intermolecular interactions. Herein, we demonstrate donor–acceptor-type CPs with NIR emission properties. In summary, the CP with a bithiophene donor bearing the bulkiest substituent exhibited excellent solid-state NIR emission (λFL = 806 nm, ΦFL = 7.5%). In addition, the longest emission maximum was obtained from the CP containing cyclopentadithiophene (λFL = 923 nm, ΦFL = 0.9%). The concept for the introduction of vertically projected bulky substituents at boron opens a new research field on solid-state NIR-emissive materials

Potential Dependence of the Buckling Structure of the Interfacial Water Bilayer on a Graphene Electrode

The interfacial structure between aqueous electrolytes and the epitaxial graphene on a SiC(0001) electrode has been determined using X-ray diffraction. The electrolyte and electrode potential dependences are investigated, and it is found that the water bilayer is stabilized on the graphene surface in a similar fashion to icelike structure. There are no specific adsorbed ions and no layer formation of electrolyte ions at the Helmholtz plane, which differs from the double-layer structure found on metal electrodes remarkably. The layer spacing of the water bilayer depends on the electrode potential, indicating that water reorientation occurs. The applied electrode potential is strongly related to the potential drop across the interface induced by the electric dipole field of the bilayer water. A small double-layer current results from non-faradaic charge by the reorientation of the bilayer water

Compression-Induced Conformation and Orientation Changes in an <i>n</i>‑Alkane Monolayer on a Au(111) Surface

The influence of the preparation method and adsorbed amount of <i>n</i>-tetratetracontane (<i>n</i>-C₄₄H₉₀) on its orientation in a monolayer on the Au(111) surface is studied by near carbon K-edge X-ray absorption fine structure spectroscopy (C K-NEXAFS), scanning tunneling microscopy (STM) under ultrahigh vacuum, and infrared reflection–absorption spectroscopy (IRAS) at the electrochemical interface in sulfuric acid solution. The <i>n</i>-C₄₄H₉₀ molecules form self-assembled lamellar structures with the chain axis parallel to the surface, as observed by STM. For small amounts adsorbed, the carbon plane is parallel to the surface (flat-on orientation). An increase in the adsorbed amount by ∼10–20% induces compression of the lamellar structure either along the lamellar axis or alkyl chain axis. The compressed molecular arrangement is observed by STM, and induced conformation and orientation changes are confirmed by in situ IRAS and C K-NEXAFS

Synthesis of Poly(dithienogermole)s

Reactions of 4,4-dichlorodithienogermoles with sodium, followed by reprecipitation of the organic products, provided poly­(dithenogermane-4,4-diyl)­s. The absorption edges were at lower energies than that of a monomeric dithienogermole derivative. Comparison of the optical properties of the polygermanes with those of their respective polygermoxanes (prepared by oxidizing the polygermanes) and copolymers composed of dithienogermole and di-<i>n</i>-butylgermane units indicated that the red-shifted absorption edges were likely associated with conjugation of the dithienogermole π-orbital with the polygermane backbone σ-orbital. This was further supported by optical studies on the dimeric compound 4,4′-bis­(4-ethyldithienogermole) and density functional theory calculations on tetrameric models

Ethanol Oxidation on Well-Ordered PtSn Surface Alloy on Pt(111) Electrode

Surface and subsurface structures of PtSn surface alloy on Pt(111) were determined using in situ scanning tunneling microscopy (STM) and X-ray diffraction. Different ordered structures of the PtSn alloy layer were observed by STM in HClO₄ at coverage of θ_Sn ≤ 0.23. Superstructure of (√3 × √7)­R19.1° with small domain size was formed at θ_Sn = 0.23. This structure promoted the catalytic activity for the ethanol oxidation reaction with high durability. X-ray structural analysis showed that the ratio of Sn in the subsurface was below 3(2)%, The PtSn alloy layer was mainly formed at the surface of the Pt(111) electrode. The Sn atoms protruded by 0.02 nm from the Pt layer, which was similar to the surface structure of Pt₃Sn­(111). One Pt atom in the (√3 × √7)­R19.1° structure contacts to one or two surrounding Sn atoms, which lead to the highest activity for the EOR

Structural Dynamics of the Electrical Double Layer during Capacitive Charging/Discharging Processes

Transitional structures of Cs⁺ at the outer Helmholtz plane (OHP) have been determined using time-resolved X-ray diffraction during the double-layer charging/discharging on the Ag(100) electrode in CsBr solution. At the double-layer potential region at which c(2 × 2)-Br is formed on Ag(100), the transient current comprises two exponential terms with different time scales: a rapid and a slow one are due to the dielectric polarization of water molecules and the transfer of Cs⁺, respectively. The slow term is composed of different dynamic processes of Cs⁺ during charging and discharging. When the potential is stepped in the positive direction, the coverage of Cs⁺ at the OHP decreases. In this step, the transient X-ray intensity at the (0 0 1) reflection, which is sensitive to the OHP structure, shows that Cs⁺ is released from the OHP according to exponential function of time. The decay of transient intensity of X-ray has a time scale similar to that of the current transient measurement. On the other hand, the accumulation process of Cs⁺ from the diffuse double layer to the OHP comprises two different kinetic processes after a potential step in the negative direction: a rapid one is the accumulation of Cs⁺ near the outer layer, and a slow one is the structural stabilization of the Cs⁺ layer

Synthesis of 4,4-Dihydrodithienosilole and Its Unexpected Cyclodimerization Catalyzed by Ni and Pt Complexes

4,4-Dihydrodithienosilole (<b>DTSH</b>_<b>2</b>) was isolated from a mixture of 3,3′-dibromobithiophene, <i>n</i>-BuLi, and H₂SiCl₂ and was fully characterized. The reaction of <b>DTSH</b>_<b>2</b> with a Pt(0) complex, prepared <i>in situ</i> from [Pt­(PCy₃)₂] and DPPE (1,2-bis­(diphenylphosphino)­ethane), produced a bis­(silyl)platinum complex [Pt­(DTSH)₂(dppe)] (<b>1</b>) with two hydrodithienosilole ligands. <b>DTSH</b>_<b>2</b> undergoes cyclodimerization accompanied by skeletal rearrangement to afford a cis-fused bicyclic compound (<b>2</b>) upon heating the solution in the presence of a catalytic amount of <b>1</b> or [Ni­(PPh₃)₄]. The product has a Si–Si bond that bridges two Si atoms, separated by 2.309(1) Å. Bicyclic disilane <b>2</b> forms the Pt complex (<b>3</b>) with two Si ligands and retaining the 10-membered macrocycle ligand via the Si–Si bond cleavage

Group 14 Dithienometallole-Linked Ethynylene-Conjugated Porphyrin Dimers

The considerably conjugated π systems of the group 14 dithienometallole-linked ethynylene-conjugated porphyrin dimers (<b>1M</b>s) were described based on comprehensive experimental and theoretical studies. The electronic absorption spectra of <b>1M</b> displayed a large splitting in the Soret band and a red-shifted Q-band, indicating that the dithienometallole spacer was effective in facilitating the porphyrin–porphyrin electronic coupling. Torsional planarization behaviors of <b>1M</b> were observed in the time-resolved fluorescence spectra. Density functional theory (DFT) calculations revealed that the dithienometallole spacer is an ideal partner for the ethynylene-conjugated porphyrin to produce fully delocalized highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels due to their similar HOMO and LUMO levels. Finally, <b>1M</b> exhibited a strong propensity for the quinoidal–cummulenic conjugation in the dithienometallole spacer when in a photoexcited state