Benzocarborane is the compound comprising fused benzene rings with o-carborane known as an icosahedral boron cluster compound. Benzocarborane is expected to be applied to electronic and optical devices because of its conjugated plane. In this work, we successfully synthesized novel dithienobenzocarborane by the intramolecular cyclization reaction of o-dithienylcarborane. We report the synthesis of dithienobenzocarborane derivatives. Their conformation and electronic state are also discussed in detail.

View full abstract

A new type of multiphenylseleno-substituted oligothiophene (1) has been prepared.The cyclic voltammogram of the tiophene (1) showed the reversible redox peak. The crystal structure and the one-electron oxidation of the thiophene (1) will be discussed.

View full abstract

We designed and synthesized various alternating carbazole-thiophene oligomers and investigated their structure-property relationships on the basis of X-ray diffraction analysis, UV/Vis and fluorescence spectroscopy, and cyclic voltammetry as well as theoretical calculations.

View full abstract

Thiophene-fused 3-methylene-2,3-dihydrothiophene derivatives 2 were synthesized by intramolecular [4+2] cycloaddition of 2-alkynyl-3-(9-anthrylthio)thiophene derivatives 1. These derivatives showed blue fluorescence in a CH2Cl2 solution and phenyl-substitution derivative indicated relatively strong fluorescence in a solid stat

View full abstract

In our previous study, we found that the dications of thiophene-pyrrole oligomers composed of 8 or 9 five-membered heterocycles have a biradical character. In this work, we have focused benzodithiophene where thiophene is annelated with benzene. We have developed new synthetic route to benzodithiophene frameworks and investigated the effect of benzodithiophene frameworks binding to thiophene-pyrrol-thiophene frameworks on the biradical character of the dications.

View full abstract

Peptide-inspired bis(3-ethynyl-2-thienyl)arene derivatives, containing a main axis and ethynyl side chains, were prepared and their properties were studied. Some related compounds were also prepared and their crystal structures were studied.

View full abstract

Phenazasiline-thienylene-phenazasiline type compounds were prepared and the effect of the number of introduced thiophene unit was investigated. Bis(phenazasiline)s containing thiophene unit were prepared from Pd(0)-catalyzed coupling reaction between 2-bromo-8-methylphenazasiline and distannylthiophenes. Bis(phenazasiline) without thiophene unit was prepared by coupling reaction of 2-bromo-8-methylphenazasiline by using Ni(0) complex. Investigation of the effects of the number of introduced thiophene unit of the compound was carried out by measurement of absorption and fluorescence spectra, cyclic voltammetry, and X-ray analysis.

View full abstract

Molecular orientation of pi-conjugated systems has a great influence on their solid-state properties. As a simple strategy for the design of molecular assembly, we now propose the concept of flexible double-chain linkage between two pi-components. A series of terthiophene dimers, in which terthiophene units are linked by two flexible alkyl chains, have been designed and synthesized. These compounds showed significant dependence of their solid-state properties on the linker chain lengths in terms not only of solubility, gelation ability, and phase transition behavior, but also of the solid-state fluorescence. In particular, the difference in the solid-state emission maxima exceeds more than 100 nm between symmetrical parallel dimer and unsymmetrical twisted dimer.

View full abstract

Control of packing structures of pi-conjugated system in the solid state is crucial for gaining attractive photophysical properties and high charge transporting ability. We here designed and synthesized bi(thieno[2,3-c]thiophene)s with various terminal aryl groups at 6,6'-position. Among them, the CF₃-substituted derivatives were found to form J-aggregates with significantly red-shifted fluorescences in crystal.

View full abstract

We previously synthesized polydiazo compounds consisting of two diphenyldiazomethanes by using Sonogashira coupling reaction and generated high spin polycarbenes by their photolysis. In this work in order to simplify the synthesis, we synthesized homopolymerizable diphenyldiazomethane having two iodine groups at the 3,5 positions and an ethynyl group at the 4' position and characterized the corresponding carbene generated by its photolysis. In addition, we attempted to homopolymerize the diazo compound.

View full abstract

Localized 1,3-biradicals can be formed in the photochemical denitrogenation of 2,3-diazabicyclo[2.2.1]hept-2-ene (DBH) derivatives. In this study, we found that the unusual beta-CC cleavage reaction was observed when the substituents at the methano bridge carbon of the DBH derivative AZ was propylene ketal (-O(CH₃)₃O-). We will discuss the mechanism based on our experimental results and quantum mechanical calculations, including the role of the substituent on the reactivity of the triplet state of azoalkanes.

View full abstract

In general, localized singlet biradical are short-lived, thus, it is quite difficult to observe them spectroscopically. The long-lived singlet state molecule is indispensable to detect the species. We have succeeded to observe the singlet biradical at ns time scale by generating the 2,2-dialkoxy-1,3-diyls. . We report herein the aryl-group (Ar = Ph, p-CNPh, 2-furanyl,3-furanyl) effect on the reactivity of singlet biradicals, including the lifetime.

View full abstract

We have recently reported that (nitronyl nitroxide)-substituted dihydrophenazine radical cations exhibit interesting magnetic properties. For further development of this system, we have designed and synthesized a neutral dihydrophenazine derivative with two nitronyl nitroxides at 2,7-positions and its oxidized cationic species. We clarified 1) the neutral diradical species shows a weak ferromagnetic interaction between the two nitronyl nitroxides, 2) the cationic species exhibits a strong ferromagnetic interaction between the dihydrophenazine radical cation and the two nitronyl nitroxides. The structures and properties of these species will be described.

View full abstract

Ladder-type quinoidal molecules of carbon-bridged phenylenevinylenes were designed and synthesized. The novel biradical nature was confirmed by ESR and SQUID measurements and further elucidated by theoretical calculations. Compared to the corresponding aromatic precursors, the band gaps of the compounds remarkably decreased, which are in agreement with the biradical feature. Significantly high stability was observed in solid and solution states, which can be ascribed to the anti-oxidation ability due to deep HOMO levels confirmed by DPV measurements. Unexpectedly, near-infrared (NIR) emission was observed at room temperature for both compounds. Both compounds afford stable dianion species by electrochemical and chemical reduction, accompanied with emission switching behavior.

View full abstract

In this study, we have prepared spirobi(triarylamine)s containing nitroxide groups as localized spin units. In the oxidized states for the spiro molecules, we expected intramolecular ferromagnetic interaction between the localized spins and the delocalized spins. There exists the possibility that the radical cation and di(radical cation) of the spiro molecules are in spin quartet and quintet states, respectively, as a consequence of the intramolecular ferromagnetic interaction. We will report in detail on the electronic structures of the oxidized species on the basis of spectroscopic measurements.

View full abstract

In the radical cation of hexaazacyclophane 1, it was found that the generated spin is delocalized all over the molecular skeleton. In this study, we have prepared the 2-dimensionally expanded polymacrocyclic arylamine 2 to explore highly spin-delocalized giant molecules as compared to the radical cation of 1. We will report on the electronic structure of 2 on the basis of the electrochemical and spectroscopic measurements. In addition, we will discuss spin-delocalization in oxidized states of 2 in comparison with those of the other macrocyclic arylamines.

View full abstract

We have synthesized an organic radical supramolecular gelator which has both hydrophilic and hydrophobic groups in the molecule. This gelator forms a hydrogel by dissolving it in hot water, followed by cooling to room temperature. This hydrogel showed thermally reversible sol-gel transition. The sol-gel transition temperature was determined to be ca. 60 degrees by DSC analysis, polarizing optical microscopy, and EPR spectroscopy. The SEM observation revealed that a xerogel prepared from the hydrogel has a three dimensional network structure.

View full abstract

Trioxotriangulene (TOT) is a fused polycyclic neutral radical with a planar 25 pi-electronic structure. We revealed that TOT derivatives possessing alkyl or alkoxy groups and halogen atoms are extremely stable under air atmosphere in both solid and solution states and exhibit exotic magnetic, electronic, and electrochemical properties due to the extensive spin-delocalized nature and degenerated LUMOs. In this work, in order to explore a new aspect of the TOT chemistry, we have newly designed, synthesized, and isolated TOT derivatives bearing thiophene moieties. The stability, redox properties, and electronic-spin structure have been experimentally investigated.

View full abstract

Phenalenyl is an odd-alternant hydrocarbon neutral radical having a planar condensed polycyclic pi-electronic structure. We have designed and synthesized various kinds of air-stable phenalenyl radical derivatives and experimentally demonstrated their exotic magnetic, electronic, and optical properties inherently attributable to their unique spin-delocalized nature. Recently, these results inspired us to design the first optically-active phenalenyl radicals possessing helicenic structure. In this study, we have succeeded in the synthesis and isolation of the chiral phenalenyl radical as an air-stable solid. The electronic-spin structure, chiroptical properties, and racemization behavior were experimentally evaluated.

View full abstract

Pyridine and pyrimidine derivatives can form coordination bonds with metal ions at the nitrogen atoms. We have engaged in synthesis of some radical ligands including a pyridyl nitroxide group, but only a few radical ligands including a pyrimidine core are known. Hence, we will report synthesis of a novel bisbidentate ligand, pyrimidine-4,6-diyl bis(tert-butyl nitroxide), and characterization of the ground-state multiplicity by means of electron spin resonance. Some coordination compounds were prepared, in which the ligand possessed a nitroxide radical group at one side and an anionic hydroxylamine group at the other.

View full abstract

A couple of novel naphthalendiimide derivatives with a carboxy group were prepared by using glycine or beta-alanine, in which both naphthlendediimide unit being expected to exhibit sensitization and TEMPO group to have redox properties are incorporated. Similar redox properties and antiferromagnetic interactions of CW behavior were observed in both of the derivatives. The results on their activities as DSSC and the structures and properties of two kinds of carboxyphenyl derivatives will be reported at the same time.

View full abstract

Diels-Alder reaction of C₆₀ or C₇₀ with a pentacene derivative having dendritic substituent at 2,3,9,10-positions produced new fullerodendrimers in excellent yields. Interestingly, one of the two regio-isomers of the C₇₀ adducts was isolated and well characterized.

View full abstract

Fullerene C₆₀ and C₇₀ derivatives with distinctly high LUMO levels compared to pristine fullerenes can be prepared by introducing two functional groups not at 1,4-position but at 1,2-position. In this work, we conducted reactions of C₆₀ with some lithium acetylides followed by nucleophilic substitutions with various alkyl iodides to give a series of soluble 1,2-dihydrofullerene derivatives in moderate yields. Then we fabricated the bulk-heterojunction (BHJ) solar cells using the 1,2-dihydrofullerene derivatives and poly(3-hexylthiophene) as the acceptor and the donor materials, respectively. These devices marked high open circuit voltage (Voc) of 0.58 – 0.60 V, which is comparable to that of a device using the benchmark acceptor, [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM). We will discuss the characteristics of the BHJ solar cells using 1,2-fullerene derivatives in detail.

View full abstract

The functionalization of single-walled carbon nanotubes (SWNTs), which controls their solubility and electrochemical properties, is a current subject of intense research. Herein we present the substituent effect on the reductive alkylation of SWNTs using lithium or alkyl lithium and alkyl halide. This reaction showed significant substituent effects on the degree of functionalization of SWNTs.

View full abstract

X-ray analyses of the cocrystals of Gd@C_2v(9)-C₈₂ with nickel^II octaethylporphyrin (Ni ^II (OEP)) reveal that the Gd3+ cation is off-center, being located under a hexagonal ring along the two-fold axis of the C_2v(9)-C₈₂ cage. Our result is in sharp contrast to that of a previous study, showing that Gd@C_2v(9)-C₈₂ has an anomalous endohedral structure with the metal being positioned over a [6,6]-bond, which is opposite the hexagonal ring along the C₂ axis (Phys. Rev. B 2004, 69, 113412.).

View full abstract

Bis-functionalization of endohedral metallofullerene La2@C80 by carbene addition is reported herein. Adducts were characterized using spectroscopic and single-crystal X-ray structure analyses. Crystallographic data for bisadduct La2@C80(CClPh)Ad (Ad = adamantylidene) revealed that both carbene additions occur at the 6,6-bond junction on the C80 cage with ring cleavages and that La atoms are positioned collinearly with spiro carbons. It is noteworthy that the La-La distance in La2@C80(CClPh)Ad is highly elongated by carbene bis-functionalization compared to pristine La2@C80 and reported functionalized derivatives. The metal positions were confirmed through density functional calculations.

View full abstract

La-metallofullerenes show a lower reduction potential than empty fullerenes because of the intramolecular electron transfer from encaged La atom to outer fullerene cage. Recently, we have reported the interaction between La-metallofullerene and organic-donor molecule. Herein, we report the syntheses of La-metallofullerene / organic-donor dyads. NMR, vis-NIR spectra, and CV also reveal structure and electric properties of the dyads.

View full abstract

We herein report the synthesis and isolation of the endohedral metallofullerene, La@C₇₂(C₆H₅), La@C₇₄(C₆H₅), La@C₇₆(C₆H₅).

View full abstract

The radical coupling reaction of a paramagnetic endohedral metallofullerene, La@C₈₂, affords mono-substituted La@C₈₂ regioselectively. Four regioisomers of La@C₈₂CH₂C₆H₅ obtained from the reaction with benzyl radical, and were characterized by spectroscopic methods. In addition, heating the La@C₈₂ derivatives in the presence of a radical trapping reagent affords pristine La@C₈₂ in high yield.

View full abstract

No electron transfer from tetrathiafulvalene calix[4]pyrrole (TTF-C4P) to lithium encapsulated fullerene (Li@C₆₀•PF₆) occurs in a mixed solution (benzonitrile : chloroform = 1:1,v/v). Addition of tetraethylammonium chloride results in formation Li@C₆₀ radical anion and TTF-C4P radical cation by the binding of chloride at the C4P moiety, and following electron transfer from TTF-C4P to Li@C₆₀ to form the triplet radical ion pair. The triplet radical ion pair was identified by the EPR measurements. Disappearance of radical ion pair was observed upon addition of tetraethyl ammonium salt via back electron transfer.

View full abstract

D_2d-C₈₄ (23) and Sc₂C₂@ D_2d-C₈₄ attract special interest as they allow a comparison between the empty fullerene and endohedral metallofullerene with the same cage structure. In this work, we carried out the addition reaction ofD_2d-C₈₄ (23) and Sc₂C₂@ D_2d-C₈₄ to investigate the difference of reactivity between D_2d-C₈₄ (23) and Sc₂C₂@ D_2d-C₈₄.

View full abstract

It have been demonstrated that the facile silylation of fullerenes can be achieved with disiliranes, silylenes, and silyl radicals by photoreaction as reactive silicon species, which lower the oxidation potentials of fullerene derivatives due to the electron-donating property of organosilicon groups. On the other hand, it is well known that transition-metal complexes activate Si-Si bonds to react with unsaturated compounds. These fascinating results prompted us to investigate the validity of transition-metal complexes in silylation of fullerenes. Herein we report a novel silylation reaction of fullrenes catalyzed by transition-metal complexes. Thermal reactions of C₆₀ and disiliranes in the presence of transition-metal complexes afforded 1:1 adducts of C₆₀ and disiliranes.

View full abstract

Phthalocyanines (Pcs) with the TTF unit were prepared from the corresponding phthalonitriles. Optical and electrochemical properties of the products were determined with UV-vis spectroscopy and cyclic voltammetry. In order to generate cationic species, the Pcs were further treated with trifluoroacetic acid and iodine.

View full abstract

Phthalocyanines are 18pi-electron aromatic compound composed of four isoindoline units and form metal complexes in a 1:1 ratio with various transition metal ions. Although the syntheses and properties of metal complexes have been reported, those of gold complexes have not been reported expect for one paper. Moreover, the oxidation state of the gold ion and properties of the complex has not been revealed yet. We have carefully investigated the reactions using diiminoisoindoline and several gold salts to reveal that two different gold complexes were obtained. The X-ray single crystal analyses revealed that one was gold complex of phthalocyanine and the other was gold complex of novel phthalocyanine analogue. In this poster presentation, their syntheses and properties will be reported.

View full abstract

Pyrene-fused subphthalocyanine (PySubPc) synthesized from a mixed-condensation reaction of 2,7-di-tert-butyl-4,5,9,10-tetracyanopyrene and tetrafluorophthalonitrile exhibits red-shift of the Q band absorption due to alteration of the electronic structure upon fusion of a pyrene unit. The crystal structure determined by X-ray single crystallographic analysis showed linear arrangement of PySubPc, which was achieved by π-π stacking interactions between the pyrene and subphthalocyanine (SubPc) moieties. Furthermore, the curved conjugation surface of the SubPc moiety and the planar π-conjugation surface of the pyrene moiety enhanced its cocrystallization with C₆₀ molecules. Unique linear arrangement of C₆₀ was observed in the crystal structure of the cocrystallate. Similarly, pyrene-bridged subphthalocyanine dimers can be synthesized from the same precursors, and π-π stacking interactions between these dimers and C₆₀ not only in the solid state but also in solution can be highly expected. In this presentation, we will also report the properties of these subphthalocyanine analogues including their absorption, magnetic circular dichroism (MCD), and fluorescence spectra.

View full abstract

Various porphyrinoids have been invented due to their characteristic properties. Nevertheless, azacorrole, one of porphyrinoids, is virtually unexplored despite the simple structure. In this work, we have succeeded in synthesis of azacorrole through amination of dipyrrin derivatives. We will report synthesis, structure, and property of azacorroles.

View full abstract

Porphyrin possesses an 18pi-electron conjugation system and exhibits characteristic Soret and Q band absorption in the UV/vis region. The main elements at meso-positions are known to play a significant role in determining the spectral features and electronic structures of Porphyrin and its analogues. Thus replacement of meso-carbon atoms with hetero atoms, such as oxygen, sulfur, and nitrogen, causes alteration of the optical and electrochemical properties. Recently we found that meso-dioxaporphyrins can be easily synthesized from a reaction of dibromodipyrromethene in the presence of copper and the structure was elucidated by X-ray analysis. In this poster presentation, the synthesis and properties of the novel meso-dioxaporphyrin will be presented.

View full abstract

Carbazole and thiophene can be regarded as a part of porphyrinoid. We reported the synthesis of thiophene-bridged carbazole dimer, that exhibited distinct aromaticity and NIR absorption. Here, synthesis and property of oligothiophene-bridged carbazole dimers as novel expanded porphyrins are reported.

View full abstract

Treatment of N-fused [24]pentaphyrin with POCl3 in the presence of triethylamine gave a multiply-fused pentaphyrin P=O complex through N-fusion reaction and oxidative C–C bond formation between pyrrolic beta-positions. This complex displays strong 24pi antiaromatic character. The P=O complex was reduced with BH3-SMe2 to pentaphyrin P-BH3 complex.

View full abstract

Expanded porphyrins have unique properties different from porphyrins. But oligomers of expanded porphyrins are still rare and its chemistry has been an unexplored field. We have improved the synthetic protocol of oligopyrroles as precursors and synthesized phenylene-bridged hexaphyrin dimer. In this presentation, we report its properties and metal complexes.

View full abstract

Hexaphyrin is a kind of expanded porphyrin consisting of six pyrrole rings. This time, we have synthesized a novel hexaphyrin(1.1.1.1.1.0) containing two alpha, beta-linked confused pyrrole rings and 5 meso-carbon atoms. When the copper metal coordination was attempted, formation of bis metal complex having two different oxidation states of metal was confirmed for Mass and ¹H NMR spectra.

View full abstract

Coupled oxidation of [tetraarylporphyrinato]iron(III) chloride was performed by allowing the iron porphyrin to react with dioxygen, ascorbic acid, and pyridine to give biladienone as the major product and bilindione as a minor one. The meso-substituted bilindione was converted into an oxaporphyrin zinc complex by refluxing it with acetic anhydride and zinc acetate in chloroform, and it was isolated as a CF₃COO^- salt. X-ray crystallographic studies revealed that the CF₃COO group coordinated to the zinc. Oxaporphyrin zinc complexes reacted with various nucleophiles such as sodium methoxide, butylamine and aniline to give bilinone zinc complexes. Effects of substituent at the 19-position on spectroscopic properties of bilinones were studied. For example, 19-methoxybilinone was a blue pigment, while 19-anilinobilinone was a green pigment. The UV-visible spectra of various free-base bilinones were affected by the hetero atoms at the 19-position.

View full abstract

Porphyrins are macrocyclic compounds with large pi-conjugated network.Most of metal complexes of porphyrins utilize their central nitrogen atoms.Only few example of porphyrin metal pi-complexes have been reported.In order to construct novel metal complexes,meso-aryl substituted porphyrins with various fused moieties were synthesized.In this presentation, synthesis, properties and crystal structures will be discussed.

View full abstract

Azulene has high polarized structure, and stabilize ionic states like cation and anion. Di(1-azulenyl)methylium units could result in the formation of stable cationic compounds with special properties. Multistage redox systems were based on a combination of stable di(1-azulenyl)methyl cation. It has a strong absorption band appears at visible region. We here in report the synthesis of porphyrins with di(1-azulenyl)methylium units at meso-position, and their redox behavior.

View full abstract

Photoinduced charge transfer is one of the important processes for the conversion of solar energy into chemical and/or electric energies. Recently, various studies including multi-step electron transfer processes have investigated. However, these systems do not always exhibit efficient, long-lived CS states. One of the most promising strategies to obtain long-lived CS states seems to be a spin control approach. Here, we report on photoinduced charge-separation of a Pt-porphyrin-viologen dyad and a triphenylamine-Pt-porphyrin-naphthalenediimide triad. In these complexes, the Pt-porphyrin moiety acts as a triplet photosensitizer. The transient absorption spectra in nano-second laser flash photolysis exhibited absorption bands assignable to the donor radical cation and the acceptor radical anion, indicating the generation of the CS states with relatively long lifetime.

View full abstract

Porphyrin derivatives having ring-fused structures at the periphery have been intensively investigated because of their interesting properties such as extremely red-shifted electronic absorption and unique redox behaviors based on narrow HOMO-LUMO gaps. Recently, we have succeeded in the synthesis of a novel quadruply-ring-fused porphyrin, which consisted of five-membered fused ring at the meso positions. The fused porphyrin is assumed to be formed via a palladium-catalyzed Ullmann-type coupling reaction under microwave irradiation. The porphyrin was characterized by NMR and absorption spectroscopies, mass spectrometry, and elemental analysis. Its proposed structure as well as its photochemical and redox properties will be presented.

View full abstract

We investigated inclusion behavior of fullerene C₇₀ by cyclic porphyrin dimer. In the case of the nickel porphyrin complex, X-ray crystal structure analysis demonstrated that C₇₀ has an end-on orientation to the porphyrin. In contrast, in the case of the free-base complex, C₇₀ has a side-on orientation to the porphyrin and C₇₀ molecules form a zigzag chain with van der Waals contacts each other.

View full abstract

We have studied the synthesis and crystal structure of a porphyrin nanotube. In our continuing efforts along this line, we wish to report the synthesis of new cyclic porphyrin dimers having expanded pai-conjugated system.

View full abstract

We synthesized a linear porphyrin trimer (TPP-DEP-TPP) that has a meso-diethynyl Zn-porphyrin unit (DEP) and two tetraphenyl Zn-porphyrin terminals (TPP). The trimer formed stable 1:3 and 2:3 complexes in chloroform with 4-phenylpyridine and 4,4'-biphyridine, respectively. The complexation of the trimer was investigated by means of UV-vis titration. The detailed synthetic procedure and complexation of the trimer with several ligands will be presented.

View full abstract

Large aggregates of bacteriochlorophyll-c in green photosynthetic bacteria act as a light-harvesting antenna. Semi-synthetic zinc chlorins were already prepared as model compounds of bacteriochlorophyll-c and self-aggregated in vitro. Here, zinc chlorins and their dyads were synthesized, and their self-aggregates were prepared in non-polar organic media or aqueous solutions.

View full abstract