Yasuhiro Mazaki

Macrocyclic Oligothiophene with Stereogenic [2.2]Paracyclophane Scaffolds: Chiroptical Properties from π‐Transannular Interactions

The enantiomers of a new cyclic oligothiophene, bridged by two pseudo-ortho[2.2]paracyclophanes, were synthesized as a new class of the chiral π-conjugated system. Single-crystal X-ray diffraction analysis revealed a twisted structure for these oligothiophenes induced by a torsion of the cyclophane moieties. The embedding oligothiophenes into the inherent planar chirality provided a significant enhancement in circular dichroism (CD) spectra thanks to the large magnetic/electric transition dipole moments. In the dicationic state, an intramolecular π dimer was formed due to the strong interactions of the oligothiophenes. We further recorded unprecedented wide ranges of CD spectra in 250-1800u2005nm region. The transitions are reasonably described by the exciton coupling of the oligothiophenes.

Dimeric Tetrathiafulvalene Linked to pseudo-ortho-[2.2]Paracyclophane: Chiral Electrochromic Properties and Use as a Chiral Dopant

A dimeric tetrathiafulvalene installed into a chiral pseudo-ortho-[2.2]paracyclophane framework was synthesized as a novel chiral electrochromic material. This compound exhibited pronounced chiroptical properties in the UV-Vis-NIR range depending on its redox states without racemization. Each enantiomer was examined as a chiral dopant for nematic liquid crystals (LCs), and the induced helicity of the LC solvent was in accord with that of the tetrathiafulvalene compound.

Efficient Synthesis, Structure, and Complexation Studies of Electron-Donating Thiacalix[n]dithienothiophene†

A series of thiacalix[n]dithiothiophenes (n=4-10) was prepared by a facile method and X-ray analysis was used to determine the molecular structures of square- (4-mer) and pentagonal-shaped macrocycles (5-mer). In the cyclic voltammograms, reversible multielectron redox processes, which are due to electronic delocalization, were observed at low oxidation potentials. The cyclic 4-mer acted as a Janus-head cavitand for two C60 molecules, whereas the 5- and 6-mer formed stable 1:1 complexes with C60 u2009.

Attempt to pile up extrathin sashlike macromolecules (atomic sashes)

Abstract Long-chain molecules vapor deposited onto cooled graphite lie flat and form a monolayer. When such a monolayer of 17,19-hexatriacontadiyne (HTDY) is irradiated with UV light, a surface topochemical reaction takes place to convert the molecules into a single sheet of a sashlike macromolecule ( atomic sash ) comprising the rows of alkyl chains bridged by a polydiacetylene chain. We attempted to pile up the atomic sashes by repeating the vapor deposition and UV irradiation, characterizing the products at all stages by Penning ionization electron spectroscopy. It is found that the aggregation of alkyl chains in the outermost layer (atomic sash or HTDY) is essentially unchanged up to approximately three layers independent of whether the underlying layer is graphite or the atomic sashes.

Synthesis, Structure, Optical, and Electrochemical Properties of Triple‐ and Quadruple‐Decker Co‐facial Tetrathiafulvalene Arrays

Understanding the details of the electronic structure in face-to-face arranged tetrathiafulvalenes (TTFs) is very important for the design of supramolecular functional materials and superior conductive organic materials. This article is a comprehensive study of the interactions among columnar stacked TTFs using trimeric (trimer) and tetrameric (tetramer) TTFs linked by alkylenedithio groups (-S(CH2 )n S-, n=1-4) as models of triple- and quadruple-decker TTF arrays. Single-crystal X-ray analyses of neutral trimeric TTFs revealed that the three TTF moieties are oriented in a zigzag arrangement. Cyclic voltammetry measurements (CV) reveal that the trimer and tetramer exhibited diverse reversible redox processes with multi-electron transfers, depending on the length of the -S(CH2 )n S- units and substituents. The electronic spectra of the radical cations, prepared by electrochemical oxidation, showed charge resonance (CR) bands in the NIR/IR region (1630-1850u2005nm), attributed to a mixed valence (MV) state of the triple- and quadruple-decker TTF arrays. In the trimeric systems, the dicationic state (+2; 0.66 cation per TTF unit) was found to be a stable state, whereas the monocationic state (+1) was not observed in the electronic spectra. In the tetrameric system, substituent-dependent redox processes were observed. Moreover, π-trimers and π-tetramers, which show a significant Davydov blueshift in the spectra, are formed in the tricationic (trimer) and tetracationic (tetramer) state. In addition, these attractive interactions are strongly dependent on the length of the linkage unit.

Monolayer and bilayer formation of 17,19-dotetracontadiyne at a liquid/solid interface

Monolayer and bilayer of 17,19-dotetracontadiyne (DTDY) on a graphite substrate were studied by scanning tunneling microscopy at a liquid solid interface of phenyloctane solution. The orientation of the layers was examined with respect to the highly oriented pyrolitic graphite. The first layer grew very quickly with many small domains some tens of nm in diameter, and the alkyl chains of the molecule in each domain align epitaxially along the a g -axis of graphite. When the solution remains at room temperature, the second layer of DTDY grew epitaxially on the first layer and the domain size was much larger than that of the first layer.

Replacement of molecules at liquid/solid interfaces

Perylene-3,4,9,10-tetracarboxylic-dianhydride (PTCDA) in a monomolecular layer was formed onto highly ordered pyrolytic graphite (HOPG) by vacuum deposition. After 17,19-dotetracontadiyne (DTDY) in phenyloctane solution was dripped on the above sample, the tip of a scanning tunneling microscope (STM) was inserted into the solution and scanned to scratch a part of the PTCDA monomolecular layer from the HOPG substrate. DTDY molecules were observed to be adsorbed on the scratched region of the PTCDA molecular layer to form a monomolecular layer. The orientation and size of the DTDY molecular layer could be controlled by selecting the scanning direction and area of the STM tip scratch.

Synthesis, Isolation, and Skeletal Inversion of 5,10-Dihydrophosphanthrenes

Abstract Two stereoisomers, the trans form 1a and the cis form 1b, of 2,3,7,8-tetramethyl-5,10-diphenyl-5,10-dihydrophosphanthrene dioxide (1) were formed by spontaneous oxidation in air of the corresponding 5,10-dihydrophosphanthrenes 2 and were separated by recrystallization. Both 1a and 1b were characterized by X-ray crystallographic analysis, which revealed configurations at the phosphorus and conformations of the central tricyclic system. The 31P NMR of the reaction mixture showed at first two signals at −15.3 and −15.1 ppm, which shifted to 9.11 and 10.3 ppm after purification of the reaction mixture under aerobic conditions by oxidation of phosphorus atoms. The reaction of 1b with HSiCl3 in toluene-d8 at 100 °C gave no change, whereas 1a reacted with HSiCl3 to give reduced compounds 2a and 2b under the same conditions. The trans–cis isomerization of 2 occurred via vertex inversion at phosphorus atom. VT-NMR, X-ray analysis, and density functional theory (DFT) calculation showed that the conformational exchange of the cis form 1b proceeded via skeletal inversion of the tricyclic ring.

Straightforward Synthesis, Electrochemical Properties, and Gel Formation of Thiacalix[n]thiophenes

A facile synthetic approach toward thiacalix[n]thiophene homologues (n=4-6) is presented herein. Pd-catalyzed coupling of 2,5-dibromothiophene derivatives with stannyl sulfide gave various thiacalix[n]thiophenes in good yields. The optical and electrochemical properties of the produced cavitands were investigated. Furthermore, gelation was observed in some solvents.

Structures of a 17,19-Hexatriacontadiyne and Sashlike Polydiacetylene Monolayer on MoS2(0001) Studied by UHV- STM

We have observed a 17,19-hexatriacontadiyne (HTDY) monolayer on MoS2(0001) and sashlike polydiacetylene atomic sash (AS) molecules derived from the monolayer by scanning tunnelling microscopy under ultrahigh vacuum. HTDY molecules adsorbed at 150 K start to move around on the surface above 240 K to form relatively unstable columnar structures. The column is converted into the AS by UV irradiation. In most AS molecules on MoS2(0001), the alkyl chains are in all-trans conformation but their carbon planes are tilted to the polydiacetylene backbone. This conformer, which is one of the most stable structures for an isolated AS molecule, appears on MoS2(0001) because of very weak molecule-substrate interactions.