Diarylethene is a photochromic molecule, which is potentially applicable to various optoelectronic devices. In diarylethenes the pai-system of the two aryl rings is separated in the open-ring isomer, while the -system is delocalized throughout the molecule in the closed-ring isomer. Based on this idea the exchange interaction between two nitronyl nitroxide radicals connected by a diarylethene unit was photocontrolled reversibly along with photochromism. The switching efficiency is more than 150-fold. Magnetochemical and photochemical behavior of the radical-substituted diarylethene is described extensively.

View full abstract

[M(R-dmet)2]: a new class of metal-dithiolenes intermediate between [M(R-dmt)2] and [M(R,R'-timdt)2]

View full abstract

NMR chemical shifts reflect the molecular structure. Hence, variation in local environment affects chemical shielding and the change in chemical shifts of nuclei provides valuable information about the relative arrangement of the nuclei with respect to the substituents. The chemical shift changes caused by the nearby substituents can thus be applicable to the conformational analysis. Here, the details of the conformational analysis of highly flexible compounds, the configurational assignment of chiral secondary alcohols, and the elucidation of the structures of supramolecular complexes in solution will be discussed.

View full abstract

Recent Advances in the Chemistry of a Stable Divalent Silicon Compound

View full abstract

Novel endohedral fullerenes encapsulating molecular hydrogen(s) were synthesized by molecular surgery approach, which includes formation of an orifice on empty fullerenes, insertion of small molecule(s) through the orifice, and closure of the orifice.

View full abstract

Probing the Rotational Conformation Effect on the Fluorescence Behavior of Pentiptycene-Derived Oligo(p-phenyleneethynylene)s

View full abstract

Synthesis and Aromaticity of Nonplanar Pyrene Systems

View full abstract

A computational study of the gas phase reaction of trimethylsilyl cation with acetylene

View full abstract

The microscopic structures in binary liquid mixtures and in alkali metal chloride solutions were examined by analyzing the mass spectra of clusters isolated through fragmentation of liquid droplets. The cluster formation was controlled by not only the interaction energies but also their relative relationship. For the binary liquid mixtures, 1-pentanol (PeOH) was used as one component, and various organic liquid compounds were used as the other component. When the organic compounds interacting with PeOH more weakly coexist, the PeOH self-association was found to be remarkably promoted. The relative intensity of the PeOH-PeOH interaction against the PeOH–(the other component) interaction works as a key factor for the clustering. The same kind of relationship was true in the solvation for ions. The relative intensity of the ion-solvant interaction against the ion-counterion interaction works as a key factor for the solvation of ions.

View full abstract

The basic research on the generation and reactivity of short-lived intermediates, e.g. cations, anions, radicals, carbenes, etc., has greatly contributed to the construction of chemical reaction theories and the development of the synthetic reaction of functional materials. We have focused our interest on biradical chemistry. We found long-live singlet 1,3-diradicals. The ground state spin-multiplicity is controlled by the substituents at C2 position. The long-lived singlet diradicals was found to react intermolecularly with oxygen to produce an endoperoxide. In triplet biradical chemistry, the regio- and stereoselective formation of oxetanes were found in the Paternò-Büchi reaction.

View full abstract

[in Japanese]

View full abstract

We have so far prepared cyclophanes consisting of various aromatic rings such as phenanthrene and carbazole, and examined their electronic and photophysical properties, especially the excimer formation. Here, we have successfully synthesized triply-bridged N-arylcarbazolophanes via the intramolecular etherification of the precursors containing two N-aryl-3,6-bis(hydroxymethyl)carbazole moieties. Their electronic and photophysical properties were investigated in detail.

View full abstract

Ladder-type pi-conjugated molecules bearing azaborine or thiaborin frameworks were synthesized, and the structures of some molecules were determined by X-ray crystallographic analysis. The UV-vis absorption maxima of the ladder-type molecules were red-shifted in accordance with the molecular size, indicating the enhancement of pi-conjugation through the heteraborin units. The ladder-type molecules exhibited moderately strong fluorescence emission with small Stokes shifts, reflecting the rigid framework of these molecules. Theoretical calculations were carried out to elucidate the electronic effect on the electronic structure of the ladder molecules by the difference in bridging main group elements. Complex formation study with fluoride ion revealed that the nature of the bridging elements as well as the elongation of the pi-conjugation affect the Lewis acidity of the triarylborane moieties.

View full abstract

The π-extended sumanenes were synthesized and characterized. The terthiophene derivative showed the remarkable red shift and small band gap, which is rationalized by molecular orbital calculation.

View full abstract

Orientational isomers of the octaethylporphyrin-dihexylbithiophene-pyridine system (OEP-DHBTh-Py) were synthesized, by the oxidative cross-coupling reactions of the corresponding terminal acetylenes. Based on the experimental results of the protonation to the Py ring, the orientational effect of DHBTh on their electronic structures were studied. The curious features of this system in structure-property relationship will be reported in detail.

View full abstract

Porphyrin has a rigid skeleton and it is generally difficult to deform its planar structure. Confusion of one pyrrole ring causes drastic change in such situation. In N-confused porphyrin, energy barrier for rotation of the confused pyrrole ring is quite low relative to that in normal porphyrin and deformation of the macrocycle would occur more easily, which can afford a wide variety of molecular architectures. Here the rotation of pyrrole rings in porphyrins was investigated theoretically and porphyrin derivatives bearing unique structures were synthesized by utilizing pyrrole ring rotation.

View full abstract

Core-modified porphyrins are one of the porphyrin analogues, in which at least one core nitrogen atom is replaced by another atom. Although the chemistry of core-modified porphyrins has attracted much attention, phosphorous-containing porphyrins, namely "phosphaporphyrins", have not been prepared. Here we report the first synthesis of phosphaporphyrin and its aromaticity as well as optical and electrochemical properties. A phosphaporphyrin was synthesized via acid-promoted condensation of phosphatripyrrane with 2,5-bis[hydroxy(phenyl)methyl]thiophene. The NMR and UV-vis absorption spectra, and CV has revealed that the phosphaporphyrin possesses a considerable aromaticity and a relatively narrow HOMO-LUMO energy gap.

View full abstract

In organic medium, bis-prophyrins 1-4 connected by aromatic linkers self-assemble via subtle forces such as van der Waals, stacking, and CH/pai to form supramolecular dimers. The structures of bis-porphyrin dimer 1_1 were discussed using our chemical shift simulation, revealing that 1_1 mainly adopts the self-complementary structure. The binding studies of bis-porphyrin 1 with electron deficient aromatic guest 5 were carried out in chloroform. Soret and Q bands of 1 showed the characteristic changes when the addition of 5, and the large upfield shifts of its protons were observed in their complexation studies using 1H NMR spectroscopy. These results suggested that the electron deficient aromatic guests bound within the cleft of bis-porphyrin 1 via charge transfer as well as stacking interactions between the guests and the porphyrin rings. The addition of 5 into the solution of 1_1 resulted in the quick dissociation of the dimer and the formation of 1_5.

View full abstract

Snowflake-shaped porphyrin dendrimers with and without anthraquinonyl terminals 1 and ,2, respectively, were prepared. When the Zn porphyrin core in dendrimer 1 was excited in degassed THF, the intensity of the Zn porphyrin florescence decreased to 31% compared to dendrimer 1. The fluorescence spectra of dendrimers 1 and 2 were also measured in solvents of various polarities such as 1,4-dioxane, benzonitrile, and DMF. The degree of fluorescence quenching is more remarkable in polar solvent. These results suggest that the fluorescence quenching in dendrimer 1 is attributable to the intramolecular electron transfer. Comparison of the relative fluorescence intensity with reference compound suggested that the remarkable enhancement of the electron transfer rate by dendritic architectures.

View full abstract

Oligoacetylene (OA) is one of the most simple expanded -electron system, which is expected to produce enhanced physical properties. However, the stability of OAs suddenly decreases with increasing of the numbers of acetylenes. The main reason for this instability is proposed to be due to the intermolecular bond-formation reactions. To avoid these reactions, the introduction of bulky substituents on the terminal carbons is useful. Using this guideline, we systematically designed, synthesized, and characterized the properties of porphyrin substituted OAs.

View full abstract

Inspired by the switching properties benzo[b]thieno-annelated bis(spirodienone) derivative 2, we study dithieno-annelated bis(spirodienone) derivative 1 as a building block for new molecular-switching p-systems, and here report the synthesis, properties of 1 and its derivatives, especially quaterquinone 3. Compound 1 was prepared in two steps from 3,3'-dibromo-2,2'-bithiophene. Suzuki-Miyaura coupling of dibromo derivative and various arylboronic acids afforded diaryl-substited derivatives and their ring-opened form. Quaterquinone 3 was prepared from tetra-phenol derivative by oxidation. Quinone 3 is dark-green, air-stable substances, and has a strong absorption at 675 nm. The redox potentials and reversivility of 3 shows temperature dependance, which indicates that the redox process of 3 contains two pathways involving ring-opening.

View full abstract

Calix[4]arene-porphyrin conjugate (1) serves as a molecular tweezers which captures 1,4-diazabicyclo[2.2.2]octane [DABCO] (2). It is reported that the assembling formation between calix[4]arene-porphyrin conjugate and DABCO depends on the concentration of DABCO. In this presentation, the electrochemical characterizations of 1 with and without 2 is reported. Electrochemical behavior of 1 in the presence of 2 showed the cooperative two-electron oxidation of 1 based on Por/Por•+ system by forming 1: 1 inclusion complex. However, the second oxidation of the porphyrin of 1 is corresponding uncoordinated one. As for the control system, the electrochemical behaviors of the porphyrin monomer and 2 was examined.

View full abstract

In biological system, enzymes such as methane monooxugenase and P450cam carry out efficient oxidations of small hydrocarbons under mild conditioins by efficient substrates binding in their hydrophobic cavities that exist near redox active metal centers. For the first step to make high performance artificial oxidation catalysts inspired by these enzymes, we have synthesized new capsule shaped hosts 'cavitand-porphyrin' (MCP, M=H2, Zn, Ni, Pd), and reported encapsulation of small hydrocarbonmolecules into MCP. In this paper, we show various kinetic and thermodynamic data of methane encapsulation into H2CP, 1D-NMR, 2D-EXSY experiments and MP2 calculations. We will discuss abot the encapsulation process of small hydrocarbons into H2CP based on these data.

View full abstract

Stabilization of reaction intermediates is a characteristic property of enzymes, and widely regarded as an essential feature of catalytic activity. Reactive molecules can also be stabilized by encapsulation, a process that involves completely surrounding and isolating the reactive species within synthetic receptors. Here, we show that self-assembled capsules can amplify and stabilize molecules that are present in only trace concentrations in solution. Evidence is given that reversible chemical reactions take place within the capsule. Reversible encapsulation allows the direct observation of the stabilized molecules under ambient conditions, at equilibrium in the liquid phase. The system promises applications in amplification of high-energy species with reduced entropies.

View full abstract

is (1,6-methano[10]annuleno) [2,3,4-cd;2',3',4'-gh]pentalene (BMAP) has structure that two 1,6-methano[10]annulene are fused to pentalene. Dihydro BMAP was obtained, BMAP dianion and monoanion was observed by NMR. The aromaticity of annulene derivatives are evaluated by NICS values from molecular orbital calculation, and observed 1H-NMR chemical shifts of hydrogen attached methano bridge. Dianion species has peripheral 22pi system, whereas monoanion consisted of 14pi and 6pi components. Annelated annulenes (benzo, thieno, or other aromatic ring annelated derivative) are also discussed. ¹H-NMR chemical shifts and NICS values of annulated annulenes are affected by annulated position and ring size of annelated part.

View full abstract

The nitrogen-containing heterocyclic aromatic compounds such as pyridines, quinoline, isoquinoline and so on, react with Tf2O to give a corresponding cationic salts. Azulene reacts with the cationic salts through electrophilic substitution to give 1- and 1,3-substituted azulenes. The occurring dihydroheteroarylazulenes reacted with bases to give heteroarylazulenes. This new process could be considered as a coupling reaction without transition metal for the synthesis of heteroarylazulenes.

View full abstract

We synthesized molecules for possible three-dimensional optical memory by two photon absorption. Porphyrin and perinaphthothioindigo parts, conveying respectively the role of two photon absorption and molecular memory, were connected through an ethynyl linkage to extend fully the -electronic conjugation. Cis and trans pure isomers were isolated and found to be stable at room temperature under dark. Irradiation of the trans isomer at wavelength longer than 680 nm induced trans to cis isomerization with a change of the absorption spectrum. On the other hand, the cis isomer was isomerized back to the trans by irradiating at 500 nm. Two photon absorption characteristics will also be discussed.

View full abstract

The thiophene analogues of bianthrone, 2, 3, and 5, were newly synthesized and their structures and properties were examined. X-ray analysis revealed that 2 adopts the twisted form in the crystalline state (Fig.1.) in contrast to the fact that bianthrone prefers the folded form (Scheme 1.). The longest wavelength bands of 2(608 nm), 3(681 nm), and 5(621 nm) in the electronic spectra suggested that the twisted form is the preferred conformation in solution.

View full abstract

Corroles are tetrapyrrolic aromatic macrocycles. Recently, our group reported highly regioselective modification reaction of corroles by Ir-catalyzed direct borylation with Miyaura protocol. This time, we have achieved to synthesize doubly linked corrole dimers with direct linkages. The doubly linked corrole dimer showed the similar metalation behavior. Its structure was confirmed by X-ray crystal analysis as its cobalt complex. On the other hand, doubly linked corrole dimers easily oxidized by DDQ to give a product with unique properties.

View full abstract

A new procedure for the synthesis of azonia derivatives of coronene by intra-molecular photo Diels-Alder type reaction of azonia-1-thia[6]helicenes is reported. Photocyclization of 2-[2-(3-thienyl)vinyl] naphtho[1,2-a]quinolizinium and 2-(2-naphthylvinyl)thieno[2,3-a]quinolizinium salts gives 2a-azoniacoronene. The fluorescent property of the azoniacoronene-polyanion complexes are depending on the polyanionic matrices, and the cation exchange ratio of the polyion complexes also affects the optical properties.

View full abstract

[in Japanese]

View full abstract

Calixarene is one of the important building blocks in host-guest chemistry because of the capability to form a variety of inclusion compounds. To construct a novel host molecule, we are interested in replacing the methylene bridges to nitrogen atoms that can serve as additional hydrogen-bonding and functionalization sites. Recently, we have succeeded to prepare an exhaustively methylated azacalix[4]arene 1. In this conference, preparation and electrochemical oxidation behavior of 1 and the synthetic precursors will be reported.

View full abstract

Isothiouronium groups have great potential for use as an anion-binding unit in supramolecular chemistry, due to a high NH acidity for action as an ionic hydrogen bonding donor. Also the synthetic susceptibility allows us to fabricate self-organized systems of anion recognition. Here, we report isothiouronium-derived long-chain amphiphile 1 and isothiouronium-modified Au nanoparticles 2. The intrigued aspects in line with organized approach for anion recognition in aqueous media are discussed.

View full abstract

[in Japanese]

View full abstract

Thiacalix[4]arenes (1), in which methylene bridges of calix[4]arenes (2) are replaced with sulfides, have revealed themselves to be not a simple substitute for the "classical" 2 but a new molecular scaffold with intrinsic characteristic features originating from the bridging sulfur. One of the most note worthy features of 1 and its derivatives is their coordination ability toward metal ions to form not only mono- but also polynuclear metal complexes by virtue of the heterogeneous coordination site. It implies us to design polynuclear metal complexes of thiacalix[4]arenes, which should be suitable for metal catalysts. Herein we report the synthesis and catalytic applications of dinuclear titanium(IV) complexes of 1 and stereocontrolled synthesis of dinuclear borane complexes of 3.

View full abstract

We focused on cinchona alkaloids, which have been investigated in connection with their antimalaria activity, asymmetric reaction catalysts, and chiral separaters, and studied on structures of their supramolecular assemblies through intermolecular hydrogen bonds in solid state. The purpose of this study is to construct novel assembly with chiral coordination space. Cinchona alkaloids were mixed with metal salts, respectively, and recrystalixed, affording three single crystals of quinidine and dihydroquinidine with Cu(II) and quinine with Zn(II) suitable for X-ray crystallographic analysis. As a result of analysis, copper(II) complexes show a dinuclear copper center with double oxygen brides, while zinc(II) complex shows mononuclear metal center to which two molecules of quinine coordinate as ligands. Moreover, to understand the construction processes of the crystal structures, we performed the hierarchical analysis we proposed before.

View full abstract

The self-assembly of triangular hexadehydrotribenzo[12]annulene (DBA) derivatives has been scrutinized by scanning tunneling microscopy (STM) at the liquid - solid interface. The effect of solvent on the structure of the nonpolar DBA networks was investigated in four different solvents: 1,2,4-trichlorobenzene (TCB) as a polar aromatic solvent, 1-phenyloctane as a solvent having both aromatic and aliphatic moieties, n-tetradecane as an aliphatic solvent, and octanoic acid as a polar alkylated solvent. A solvent dramatically changes the structure of the DBA networks. In TCB and tetradecane, honeycomb structures with large voids were formed. The trimer structure was found in octanoic acid. In phenyloctane, triangular DBA forms a zigzag network with co-adsorbed phenyloctane. The solvent effects are discussed in terms of factors that influence the mobility of molecules at the liquid - solid interface such as solvation.

View full abstract

A flexible disk-like molecule, hexakis(tetrathiafulvalenylethynyl)benzene 1, self-aggregated in solution to form a large columnar structure in both neutral and cation radical state. By using this aggregation, nanowire and orientated film were constructed. Nanowires fabricated from both 1 and 1^•+ in CHCl₃-hexane solution have a hexagonal columnar structure, reflecting strong assembling properties. In contrast, the drop-cast films of 1 and 1^•+ exhibit an edge-to-edge closely packing arrangement, and the former shows weak FET properties. We report here the details of the nanoarchitecture fabrication of 1 and its cation radical, together with their characterization by SEM, AFM, and X-ray diffraction. The electric conductivities of the film and the wire of 1^•+•ClO₄^- were also measured.

View full abstract

6,13-Bis(alkylthio)pentacenes directed toward OFET were synthesized by the ZnI2-mediated reaction of trans-6,13-dihydroxy-6,13-dihydropentacene with alkylthiols, followed by the dehydrogenative aromatization of the resulting trans-6,13-bis(alkylthio)-6,13-dihydropentacenes with p-chloranil. The X-ray crystallographic analysis of 6,13-bis(methylthio)pentacene reveals that this compound is arranged as a result of cofacial pi-stacking with S-S and S-pi interactions.

View full abstract

A few types of 1,8-anthrylene-ethynylene cyclic oligomers with chiral structures were synthesized to examine their structures and chiroptical properties as new pi-conjugated compounds. The cyclic tetramer with two 10-n-octyl substituted anthracenes was synthesized by the Sonogashira coupling, and its enantiomers were resolved by chiral HPLC. The structure of another type of cyclic tetramer with two diacetylene linkers was constructed by a combination of coupling reactions. This compound underwent spontaneous resolution to give enantiopure samples upon crystallization. The cyclic trimers with diacetylene and acetylene linkers have strained structures as revealed by X-ray analysis and DFT calculation. Molecular design toward chiral structures with the trimeric structures is proposed.

View full abstract

[in Japanese]

View full abstract

The preparation of sp² diphenylboron cation was carried out via an adduct of diphenylchloroborane and pyridine in CD₃NO₂. However, the calculated ¹¹B NMR chemical shift (56.4 ppm) was not in accord with the experimental ¹¹B NMR chemical shift (27.4 ppm). In addition we found that as the electron donating ability of pyridine increased, the ¹¹B NMR chemical shift of sp² diphenylboron cation moved toward down field. In contrast, when the nucleophile was electron withdrawing, the experimental ¹¹B NMR chemical shift of sp² diphenylboron cation was in accord with the calculated ¹¹B NMR chemical shift of sp² diphenylboron cation. Consequently, the sp² diphenylboron cation exists in the equilibrium state between the naked sp² diphenylboron cation and the solvated sp² diphenylboron cation.

View full abstract

Iodesmic reactions were utilized to estimate the relative stability (ease of formation) of peroxy cation radicals formed by reactions of alkene cation radicals with molecular oxygen. Molecular orbital calculations with B3LYP/6-31G(d) level of theory have shown that the relative stability of the cation radicals can well be understood in terms of combination of electronic and steric effect of aryl and alkyl groups introduced in the molecules.

View full abstract

Combined experimental and computational studies were performed to obtain the mechanistic information on the selective formation of methylenecyclobutanes in the thermal denitrogenation of 3-carbomethoxy-substituted 4-spirocyclopropane-1-pyrazolines. An unprecedented mechanism involving a [2+2+2] cycloreversion denitrogenation is proposed, which is proved by the stereospecific formation methylenecyclobutanes and by trajectory calculations. The notable effect of carbomethoxy substituent on the reaction mechanism is rationalized by a hyperconjugative interaction in the transition state in the denitrogenation step.

View full abstract

[in Japanese]

View full abstract

Direct one-step hydrogen transfer occurs from an NADH analog, 10-methyl-9,10-dihydroacridine (AcrH₂) to the triplet excited state of 3,6-diphenyl-1,2,4,5-tetrazine without formation of the radical cation. On the other hand, hydrogen transfer from 1-benzyl-1,4-dihydronicotinamide (BNAH) to the triplet excited state of Ph2Tz occurs via sequential electron and proton transfer processes, when both the radical cation of BNAH and deprotonated radical are detected by the laser flash photolysis measurements. Mechanistic borderline between one-step and multistep proton-coupled electron-transfer reaction pathways in hydride-transfer reactions of NADH analogs were also examined in scandium ion (Sc³⁺)-promoted hydride transfer from AcrH₂ to 1-(p-tolylsulfinyl)-2,5-benzoquinone (TolSQ).

View full abstract

In order to clarify the origin of the alfa-effect in SN2 reactions at saturated carbon centers, 28 gas-phase reactions have been examined computationally by using the high level G2(+) method. The reactions include: Nu- + CH3X -> CH3Nu + X- [X = F and Cl; Nu- = HO-, HS-, CH3O-, Cl-, Br-, HOO-, HSO-, FO-, ClO-, BrO-, NH2O-, and HC(=O)OO-]. It was found that all alfa-nucleophiles examined exhibit downward deviations from the correlation line between the overall barriers and proton affinities for normal nucleophiles, indicating the existence of the alfa-effect in the gas phase. The transition state (TS) for the alfa-nucleophiles are characterized by less advanced C-X bond cleavages than the normal nucleophiles, leading to smaller deformation energies and overall barriers. The size of the alfa-effect is related to the electron density on the alfa-atom, and increases when the position of alfa-atom is changed from left to right and from bottom to top in the periodic table.

View full abstract

Richard et al have determined the lifetime of ring-substituted 1-phenylethyl cations in 50/50 water/trifluoroethanol (I = 0.5, NaClO₄) by use of azid clock, and discussed the mechanistic transition from S_N1 to S_N2 based on the lifetime of these cations. The 1-phenylethyl cation having nitro group has very short lifetime. We are interested in the existence of such an unstable carbocation. Then, we have discussed the solvolysis mechanism of 1-phenylethyl tosylates having electron-withdrawing substituents based on ^-18O-scrambling of starting tosylate during solvolysis.

View full abstract

Ab initio MO calculations were carried out, at the MP2/6-311++G(d,p)//MP2/6-311G(d,p) level, to investigate the conformational Gibbs energy of 2-substituted oxanes and 1,3-dioxanes (Z = OCH3, F, Cl, Br). It has been found that the Gibbs energy of axial conformers is smaller than that of corresponding equatorial conformers in every case. In the axial conformers, the interatomic distance between Z and an axial C-H separated by four covalent bonds has been found appreciably shorter than the van der Waals distance, suggesting the importance of 5-member CH/n hydrogen bonds. NBO charges of the relevant protons and carbons have been shown noticeably different. In view of these findings, the CH/n hydrogen bonding has been suggested to play an important part in stabilizing the axial conformers; this may be a cause of the anomeric effect.

View full abstract

The electronic absorption and circular dichroism (CD) spectra of a blue flower pigment of Commelina Communis, commelinin, have been studied theoretically in order to understand the origin of the blue color. The UV-visible absorption and CD spectra of the anthocyanin units in commelinin were calculated on the basis of the exciton coupling theory. The calculated spectra reproduced split absorption bands and intense CD couplets observed within commelinin. The red shifted absorption band observed at 645 nm in aqueous solution of commelinin can be attributed to the electronic excitation from the ground state to the exciton state, which is polarized to the D3 axis. These spectral properties were also supported by time-dependent density functional theory (DFT).

View full abstract