Keita Tani

Cyanamide- andoxa-bridged [3.n](3,9)carbazolophanes 1n and 2n (n = 4 and 5) were synthesized. X-ray analysis Of 14 and 25 revealed that carbazole rings are taken to be partially overlapped geometry. Electronic spectra of 1n and 2n (n = 4 and 5) showed the existence of transannular pi-pi electronic interaction between two carbazole rings, whereas fluorescence of these carbazolophanes indicated monomer-like emission.

Asymmetric epoxidation of (E)-chalcone with alkaline hydrogen peroxide by novel chiral phase-transfer catalysts (chiral PTCs) with quaternary ammonium salts of azacrown ether proceeded in high yield and good enantioselectivity. Remarkably, this reaction depended on the length of the carbon chain on the nitrogen atom with the chiral PTCs and on the bulk of the base. (c) 2006 Elsevier Ltd. All rights reserved.

The interplanar interactions for fully overlapped (FO) and partially overlapped ( PO) carbazole dimers were investigated using zero field splitting (ZFS) parameters D and E in the excited triplet (T-1) states. The observed D value decreases from the monomer to the dimers due to electron delocalization in the T-1 dimers. The highest electron delocalization was observed within the two planes of the FO dimer. The interplanar interactions were analysed in terms of exciton (EX) and charge resonance (CR) types interactions by comparing the D values of monomer and the dimers. It is found that about 90% of excitation is delocalized over the two carbazole units in the T-1 state of the FO dimer whereas for PO this contribution is 40%. In a model system, D-CR and E-CR were calculated using the two approximations, point charge and half point charge, for the evaluation of the ZFSs obtained.

The photophysical properties of a series of triply bridged [3.3.n](3,6,9)carbazolophanes ([3.3.n]Cz, n = 3, 4, 5, 6) were studied as a model compound for a fully overlapped carbazole excimer. In these [3.3.n]Cz molecules, a plane angle of the two carbazole moieties changed systematically from nearly parallel to oblique, with increases in the length of the methylene chain n bridging at the 9-position of each carbazole ring. Absorption bands of [3.3.n]Cz showed the blue-shift and the splitting for L-1(a) <- (1)A and L-1(b) <- (1)A transition bands of the reference carbazole monomer, respectively. These spectral changes in [3.3.n]Cz were explained by Kasha's molecular exciton theory with the distance r and dihedral angle theta between the carbazole moieties in the ground state. In both liquid and glass matrixes, [3.3.n]Cz showed intramolecular excimer emission. The emission peak wavelength changed from 409 nm (n = 6) to 480 nm (n = 3) depending on r in the ground state. The dependence of the peak wavelength on r clearly showed that relative configurations of carbazole moieties in the ground state were preserved even in the excimer states. The smaller radiative rate of the excimer emission than the reference monomer was explained by the dimer symmetry of [3.3.n]Cz.

Photoinduced intramolecular charge separation (CS) in a polar polymer glass, cyanoethylated pullulan (CN-PUL), was studied below the glass transition temperature (T-g=395 K). A series of three carbazole (Cz: donor)-cyclohexane (S: spacer)-acceptor (A: acceptor) molecules (Cz-S-A) was used as intramolecular donor-acceptor dyads. The photoinduced CS rate was evaluated by the fluorescence decay measurement at temperatures from 100 to 400 K. The CS rate (k(CS)) increased above 200 K even far below T-g where micro-Brownian motions of the whole polymer chain are frozen. Below 200 K, on the other hand, k(CS) showed weak dependence on temperature. The temperature dependence of k(CS) is discussed in terms of the dielectric relaxation time of the polymer matrix. Consequently, CS below T-g was well explained by a thermally nonequilibrium electron transfer (ET) formula above 200 K and by a two-mode quantum-mechanical ET formula below 200 K. The increase in k(CS) above 200 K is mainly caused by a thermally activated low-frequency matrix mode originating from the side-chain relaxation of polar cyano groups. The weak temperature dependence of k(CS) can be explained by a nuclear-tunneling effect caused by a high-frequency matrix mode (h omega(H)=250 cm(-1)) and an intramolecular vibrational mode (h omega(Q)=1300 cm(-1)). The high-frequency mode of the polymer matrix was attributed to a vibrational or librational motion of polar groups in the CN-PUL glassy solid. (c) 2005 American Institute of Physics.

The rate of photoinduced intramolecular charge separation (CS) k(CS) in polymer solids was evaluated by the fluorescence lifetime measurement over a temperature range 100-400 K. Nine kinds of carbazole-spacer-acceptor dyads (Cz-S-A) were embedded in a series of poly(alkyl methacrylate) films with various glass transition temperatures (T-g's). The rate k(CS) of Cz-S-A increased above T-g or melting temperature T-m of each polymer solid. The temperature dependence of k(CS) in a poly(butyl methacrylate) glassy solid was in agreement with that of the dielectric constant at higher frequencies, indicating that orientational motions faster than the CS rate are effectively coupled to the CS event. The effective dielectric constant (epsilon') for CS was evaluated with a novel fluorescent probe of carbazole-terephthalate cyclophane (Cz-TP). The free energy gap and temperature dependence of k(CS) were well explained by a single quantum mode electron transfer (ET) formula with epsilon' rather than a static dielectric constant epsilon(S) in a poly(butyl methacrylate) glassy solid. In conclusion, CS in poly(alkyl methacrylate)s is promoted above T-g or T-m by enhancement in orientational motions of ester groups with a relaxation time comparable to the CS event.

The palladium complexes of highly extended pi-electronic conjugation system, octaethyl porphyrin (Pd)-(dihexylbithiophene)(n)-octaethylporphyrin(Pd) [OEP(Pd)-(DHBTh)(n)-OEP(Pd), n=1-6], were synthesized, in which all the chromophores are connected with diacetylene linkage. The unsymmetrical derivatives of OEP(Ni)-DHBTh-OEP(Pd) were also successfully synthesized. Electronic properties of these symmetrical and unsymmetrical complexes were conclusively described, as compared with those of OEP(Ni)(DHBTh)(n)-OEP(Ni). Based on the structure elements, a methodical guiding principle for molecular design of the particular electronic structure will be proposed. (C) 2004 Elsevier Ltd. All rights reserved.

A novel rigid fluorescent probe, carbazole - terephthalate cyclophane (Cz-TP) was applied to evaluate local dielectric constants (E) of various polymer solids in a wide range of temperatures. For poly(vinylidene fluoride), the e increased above the glass transition temperature (T-g), due to relaxations of the polar segment -(CH2CF2)- of the main chain. For poly(alkyl methacrylate)s, the epsilon increased above the T-g or the melting temperature of the side chain, where motions of the polar ester groups are activated. For cyanoethylated polymers, the epsilon increased owing to motions of the polar cyano groups at the end of the side chain and the e corresponded to the dielectric constant evaluated by dielectric relaxation measurement at a high frequency, because the Cz-TP exciplex has a lifetime of tens of nanoseconds. For a cyanoethylated polymer with a high content of cyano groups, the e was larger at low temperatures than the dielectric constant obtained by the macroscopic dielectric relaxation measurement. These results show that the Cz-TP molecule is a useful probe for evaluation of the local polarity in polymer solids over a wide temperature range and can detect even a small change in - at transition temperatures such as glass transition, side-chain melting, and side-chain relaxation. (C) 2004 Elsevier Ltd. All rights reserved.

Photophysical properties of carbazole-terephthalatc cyclophane (Cz-TP) were Studied. The absorption spectra of Cz-TP in various solvents were slightly broadened due to the distortion of the carbazole (Cz) moiety and became similar to that of a reference compound of carbazole-benzene cyclophane (Cz-Bz). The absorption spectrum and the peak wavelengths of Cz-TP were insensitive to the solvent polarity. These findings show that there is transannular pi-pi electronic interaction between the Cz and TP moieties but that the charge transfer interaction from the Cz to TP moieties is small in the ground state. On the other hand, the emission spectrum was broad, structureless, and red-shifted compared with that of the reference compound. The peak wavelength of the emission was shifted to a longer wavelength with increases in the dielectric constant of solvents. The peak shift was quantitatively explained by the Lippert-Mataga formula. Therefore, we conclude that the broad emission is due to the intramolecular exciplex in Cz-TP. The dielectric constant of 2-methyl tetrahydrofuran was evaluated from the exciplex emission of Cz-TP ranging from 77 to 292 K, indicating that the Cz-TP molecule is an excellent polarity probe not only in a liquid phase but also in a solid phase over a wide temperature range.

As a first example of carbazole-acceptor cyclophane, carbazole-terephthalate cyclophane 1a was prepared. The structure of 1a was characterized by H-1 NMR and X-ray analysis. Absorption spectrum of 1a showed the existence of transannular pi-pi electronic interaction and little charge transfer interaction. Fluorescence spectrum of 1a in THF exhibited intramolecular exciplex emission around 525 nm.

The intramolecular [2 + 2] photocycloaddition of a,omega-bis(3,6-divinyl-N-carbazolyl)alkanes 3 afforded triply bridged syn-[2.2.n] (3,6,9)carbazolophanes 4a-6a (n = 4) and 4b,5b (n = 5) composed of isomers derived from the difference in the direction of cyclobutane rings. In major isomers 4a and 4b, excimer fluorescence was observed, the maximum position remarkably depending on the tether length.

[2.2]Paracyclo(3,6)carbazolophane (1a) and [2.2](1,4)-naphthaleno(3,6)carbazolophane (1b) were prepared. The structures of 1a and 1b were characterized by H-1 NMR. X-ray analysis of 1a revealed that the carbazole ring extremely deviates from the conjugated plane. Electronic spectra of 1a and 1b showed the broadening and bathochromic shift compared with the references.

The photophysical properties of carbazole excimers were investigated using syn- and anti-[3.3](3,9)carbazolophanes: the syn-carbazolophane is a model compound for a fully overlapped carbazole excimer and the anti-carbazolophane for a partially overlapped carbazole excimer the structures of which have been determincd by X-ray analysis. H-1 NMR spectra showed that two carbazole moieties in the syn- and anti-[3.3](3,9)carbazolophanes did not flip even in solution owing to short [3.3](3,9)link-ge: geometrical alignments of two carbazole moieties remained the same as those determined by the X-ray analysis. Absorption bands of the carbazolophanes were broadened and blue- or red-shifted compared with those of l,3-bis(3-methyl-N-carbazolyl) propane used as a reference compound. These spectral features were explained by Kasha's molecular exciton theory. Fluorescence spectra of both carbazolophanes were red-shifted, broad, and structureless hands. These broad emissions were ascribed to intramolecular excimer fluorescence of the carbazolophanes, which was insensitive to solvent polarity. The dipole moment in the excited state was estimated to be similar to0 D for die anti-carbazolophane and to be 4.8 D for the syn-carbazolophane from Lippert-Mataga plots. The radiative rate of excimer emission was 3.4 x 10(6) s(-1) for the anti-carbazolophane and 7.2 x 10(5) s(-1) for the syn-carbazolophane. Our [3.3] (3,9) linkage carbazolophanes clearly showed that these different photophysical properties of carbazole excimers; result from the geometries of their carbazole moieties.

syn- And anti-[3.3](3,9)carbazolophanes, which are suitable model compounds for sandwich and partial-overlap excimers, respectively, have been synthesized and characterized; the structures of both singlet and triplet carbazole excimer have been described.

An extended pi -electronic conjugation system of dihexylbithiophene-octaethylporphyrin [OEP-(DHBT)(n)-OEP; n = 1-5], all the chromophores in which are connected with the linkage of 1,3-butadiyne (diacetylene), was synthesized by an oxidative cross-coupling reaction of the corresponding terminal acetylenes. Absorption spectral and electrochemical properties of the OEP-(DHBT)(n)-OEP system were examined. The results proved that the orientation of two 3-hexylthiophene (3HTh) rings of DHBT plays an important role in electronic communications between the two terminal OEP rings.

Macropolycyclic cage compounds were synthesized by a direct reaction between diamines and bis(bromomethyl) compounds. The procedure for constructing the polycyclic cage structure is simple and straightforward. The macropolycyclic compounds obtainable from this cyclization procedure are three-dimensional cage compounds, and any other isomers were not obtained except for two examples. Benzene, pyridine, and aliphatic units could be introduced into the cage structure. The macrocycles that have strong cation affinity were obtained as their potassium complexes.

Various mixed complexes of vinylene-bridged bis- and tris(octaethylporphyrin)s (bis(OEP)-(M1-M2) and tris(OEP)-(M1-M2-M3)) with d8 transition-metal ions M(II) (M: M1, M2, and M3 = Ni or Pd or Pt) were synthesized by step-by-step and selective metallations of the respective free-bases (FB) with limited amounts of the metallation reagent. Metallation of tris(OEP)-(H2-H2-H2) started in the central OEP ring, with the vinylene linkages of the product retaining the same (E,E)-configuration as those in FB. On the other hand, metallation of (E)-bis(OEP)-(H2-H2) afforded the corresponding (E)-bis(OEP)-(M1-M2) predominantly, while metallation of (Z)- bis(OEP)-(H2-H2) was accompanied by a ready isomerization of the vinylene linkage to afford each pair of (E)- and (Z)-isomeric complexes under the similar conditions. Electronic absorption spectra of tris(OEP)-(M1-M2-M3) proved to be affected especially by the central OEP-M2 ring and by the heavier metals more intensively, resulting in the largest splitting of the Soret band for the Ni-Pd-Pt complex. Examination of the oxidation potential E1 values indicated that the electron-releasing abilities of tris(OEP)-(M1- M2-M3) are intensively reduced for the complex carrying at least two consecutive heavier metal OEP rings. In the case of bis(OEP)-(M1-M2), the (E)-isomeric series exhibited the reduction of the electron-releasing abilities regularly in order of the heavy metal complexes similarly to tris(OEP)-M, while the (Z)-isomeric series exhibited little dependence of the electron-releasing abilities upon the incorporated metals M.

The synthesis of the title compound, a triple-layered cyclophane, is described. The unusually strained structure was supported by its H-1 NMR spectra, electronic spectra, and X-ray crystallographic analysis.

Complexes of vinylene-bridged bis- and tris(octaethylporphyrin)s (bis(OEP)-M and tris(OEP)-M) with d(8) transitionmetal ions (M = Ni(II), Pd(II), and Pt(II)) were synthesized. Metalation of (E)-bis(OEP)-H-2 was carried out under the same conditions as for the corresponding octaethylporphyrin complex (OEP-M), to afford a mixture of complexes bearing the vinylene-linkages with (E)- and (Z)-configurations. On the other hand, metalation of tris(OEP)-H-2 afforded the single product of which two vinylene-linkages remained holding the same (E, E)-configuration as that in the free-base. H-1 NMR spectra varied more drastically for O-bis(OEP)-M, with respect to those of OEP-M, while electronic absorption spectra did more drastically for the (E)-isomers. Their electronic properties at the ground state were examined, proving that the interaction between the constituent OEP rings through the vinylene-linkages is more intensive for tris(OEP)-M than for bis(OEP)-M and more intensive for the Ni complex than for the Pd and Pt ones.

Both syn- and anti-[2.n](3,9)carbazolophanes (n = 4, 5) were obtained by the intramolecular [2 + 2] photocycloaddition of bis(3-vinyl-N-carbazolyl)alkanes. In the case of n = 4, the syn-isomer afforded sandwich excimer fluorescence, whereas the anti-isomer gave monomer fluorescence. (C) 1999 Elsevier Science Ltd. All rights reserved.

Novel self-filled azacalixarenes were synthesized following a simple method. The structure of a. p-xylylene-bridged compound was investigated by Xray crystallographic analysis. Compound 1:C-42:H-44 O4N2, monoclinic,space group C2/c, a = 17.236 (4), b = 9.244 (3), c = 22.217 (4) Angstrom, beta = 101.23 (1)degrees, D-calc 1.226 g/cm(3), V = 3472 (1) Angstrom(3), Z = 4, R = 0.042. The final cycle of full-matrix least-squares refinement was based on 2201 observed reflections [I>3.00 sigma(I)] and 284 variable parameters. Dynamic NMR and MM3 calculations were also employed to study the structures in solution. Azacalix[4] skeletons are rigidly fixed in shallow cone conformations and bridging xylylene units (p- and m-) are located in the cavities of the cyclic skeletons. Intra-cavity hydrogen bonds between OH and N atoms localize at low temperatures. The free energy of the localization was estimated to be 10.8 and 11.2 kcal mol(-1) for p- and m-xylylene-bridged compounds, respectively.

The cage type compounds 1 and 2 form stable Cu+ or Ag+ complexes, which have been employed for the preparation of cation-free host molecules. A reaction between the potassium complex K(+)subset of 1 and a Cu-II salt generates a Cu-I complex, The Cu-II/Cu-I redox potential is observed at +0.43 V (vs. SCE) in the cyclic voltammetry, which shows that the Cu+ state is stabilized by its rigid molecular skeleton and spatially fixed coordination sites, A reaction between Ag+ and K(+)subset of 2 yields the dinuclear complex 2Ag(+)subset of 2, which has a short Ag+...Ag+ distance (2.78 Angstrom). The halide anions (Cl-, Br-, I-) remove one Ag+ from 2Ag(+)subset of 2 to give Ag(+)subset of 2, but further demetallation does not occur, CV measurements show that these silver complexes are electrochemically stable, Both silver complexes are stable to sunlight, The first preparations of guest-free hosts have been achieved by treating Cu(+)subset of 1 or 2Ag(+)subset of 2 with CN-. Inclusions of neutral guests (NH3, BH3) have been attempted using these guest-free hosts.

Dioxa[3.3](3,6)carbazolophane 1 has been synthesized by the cyclization reaction between 3,6-bis(hydroxymethyl)carbazole and corresponding dibromide. The transannular pi-pi electronic properties of 1 in solution were examined by absorption and emission spectra. The structure of 1 was confirmed by X-ray crystal analysis.

The two isomers of tetrakisbridged dimethoxybiphenylophanes, 1 and 2, have been synthesized. With respect to the Longest wavelength absorption bands due to the biphenyl chromophores, the cross-orientation isomer exhibited the marked bathochromic shift, while the parallel-orientation isomer the typical exciton splitting. Their transannular properties in solution were further confirmed by X-ray crystal analysis.

A one-pot synthesis of 2-substituted 3-nitropyridines was developed by a ring transformation of 6- or 4-substituted 1-methyl-3,5-dinitro-2-pyridones (2 or 3) with ammonia and enamines derived from ketones. Some intermediates having a 2,6-diazabicyclo[3.3.1]nonane skeleton were isolated from reactions of 3. The ring transformation proceeds via an addition-addition-elimination-elimination mechanism. Few competitive isomeric by-products, 4-substituted 3-nitropyridines and 4-nitroanilines, were formed. All the 2 substrates showed good reactivity, but the 3 substrates having electron-withdrawing substituents were less reactive and selective. 1,4,6-Trimethyl-3,5-dinitro-2-pyridone did not gave any products. The selectivity is interpreted in terms of differences of thermodynamic (main selection rule B) and kinetic stability (minor selection rule A) between the possible bicyclic intermediates which are expected to be formed via the mechanism.

2-Methyl-4-nitro-5(2H)-isoxazolone (1) was found to be a versatile precursor for a functionalized nitrile oxide by reaction with dipolarophiles giving 3-(N-methylcarbamoyl)isoxazole (2 or 3) derivatives.

New ring transformations of 3,5-dinitro-1-(4-nitrophenyl)-4-pyridone and its homologues with hydroxylamine were found to give 4-nitro-5(2H)-isoxazolone. These results were rationalized by double ring transformations in sequence. The fact that the 4-position of the 4-pyridone behaved as an electrophlic site was the first example in this series of ring transfomations, and was caused by the alpha-effect of the reagent. Some reactions of the isoxazolone were carried out.

Regioselective synthesis of 2-substituted 3-nitropyridines was achieved by one-pot reaction of either 4- or 6-substituted 1-methyl-3,5-dinitro-2-pyridones with ketones in the presence of ammonia. The selectivity is interpreted in terms of steric factor of substituent on the pyridone.