Keita Tani

SYNTHESIS AND PHOTOPHYSICAL PROPERTIES OF SYN- AND ANTI-2.N(3,9)CARBAZOLOPHANES

Abstract 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.

A novel nitrile oxide precursor ; 2-methyl-4-nitro-5(2H)-isoxazolone

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

Synthesis and properties of tetrakisbridged parallel- and cross-orientation biphenylophanes

Abstract 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.

Synthesis and photophysical properties of [3.3](3,9)carbazolophanes

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.

Stable Cu + , Ag + complexes of aza-bridged macrocyclic molecules: structure and chemical properties

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+⊂1 and a CuII salt generates a CuI complex. The CuII/CuI 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+⊂2 yields the dinuclear complex 2Ag+⊂2, which has a short Ag+ · · · Ag + distance (2.78 A). The halide anions (Cl-, Br-, I-) remove one Ag+ from 2Ag+⊂2 to give Ag+⊂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+⊂1 or 2Ag+⊂2 with CN-. Inclusions of neutral guests (NH3, BH3) have been attempted using these guest-free hosts.

Dynamical Excimer Formation in Rigid Carbazolophane via Charge Transfer State

Formation dynamics of intramolecular excimer in dioxa[3.3](3,6)carbazolophane (CzOCz) was studied by time-resolved spectroscopic methods and computational calculations. In the ground state, the most stable conformer in CzOCz is the anti-conformation where two carbazole rings are in antiparallel alignment. No other isomers were observed even after the solution was heated up to 150 °C, although three characteristic isomers were found by the molecular mechanics calculation: the first is the anti-conformer, the second is the syn-conformer where two carbazole rings are stacked in the same direction, and the third is the int-conformer where two carbazole rings are aligned in an edge-to-face geometry. Because of the anti-conformation, the interchromophoric interaction in CzOCz is negligible in the ground state. Nonetheless, the intramolecular excimer in CzOCz was dynamically formed in an acetonitrile (MeCN) solution, indicating strong interchromophoric interaction and the isomerization from the anti- to syn-conformation in the excited state. The excimer formation in CzOCz is more efficient in polar solvents than in less polar solvents, suggesting the contribution of the charge transfer (CT) state to the excimer formation. The stabilization in the excited state is discussed in terms of molecular orbital interaction between two carbazole rings. The solvent-polarity-induced excimer formation is discussed in terms of the CT character in the int-conformation.

One-step Syntheses of p- and m-Xylylene-bridged Azacalixarenes and Their Rigid Molecular Skeletons

Abstract Novel self-filled azacalixarenes were synthesized following a simple method. The structure of a p-xylylene-bridged compound was investigated by X-ray crystallographic analysis. Compound 1: C42H44 O4N2, monoclinic, space group C2/c, a = 17.236 (4), b = 9.244 (3), c = 22.217 (4) A, β = 101.23 (1)°, D calc 1.226 g/cm3, V=3472 (1)A3,Z=4,R = 0.042. The final cycle of full-matrix least-squares refinement was based on 2201 observed reflections [I>3.00[sgrave](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.

Regioselective synthesis of 2-substituted 3-nitropyridines by one-pot reaction of either 4- or 6-substituted 1-methyl-3,5-dinitro-2-pyridones with ketones and ammonia

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

Development of a fluorogenic small substrate for dipeptidyl peptidase-4

A series of aniline and m-phenylenediamine derivatives with electron-withdrawing 3,3,3-trifluoropropenyl substituents were synthesized as small and chemically stable fluorescent organic compounds. Their fluorescence performances were evaluated by converting 2,4-disubstituted aniline 1 to the non-fluorescent dipeptide analogue H-Gly-Pro-1 for the use as a fluorogenic substrate for dipeptidyl peptidase-4 (DPP-4). The progress of the enzymatic hydrolysis of H-Gly-Pro-1 with DPP-4 was monitored by fluorometric determination of 1 released into the reaction medium. The results suggest that 1 could be used as fluorophore in OFF–ON-type fluorogenic probes.

Aqua­{4,4′,6,6′-tetra­fluoro-2,2′-[(piperazine-1,4-di­yl)dimethyl­ene]diphenolato}copper(II)

In the title compound, [Cu(C18H16F4N2O2)(H2O)], the CuII atom shows a distorted square-pyramidal coordination geometry with the N,N′,O,O′-tetradentate piperazine–diphenolate ligand forming the basal plane. The apical site is occupied by the O atom of a coordinated water molecule. Neighbouring complexes are associated through intermolecular O—H⋯O and O—H⋯F hydrogen bonds between the water molecule and a phenolate O atom or an F atom from an adjacent ligand, respectively, forming a centrosymmetric dimer. Dimers are linked by additional intermolecular C—H⋯O and C—H⋯F hydrogen bonds, giving infinite chains propagating along the a axis.