Hirotsugu Tomiyasu

An Efficient Approach to the Synthesis of Novel Pyrene-Fused Azaacenes

An efficient synthetic approach for functionalization of both the active sites (1,3-) and the K-region (4,5,9,10-) of pyrene was accomplished by bromination and oxidation with considerable yield. These novel pyrene-fused azaacenes were thoroughly investigated by X-ray diffraction studies, electrochemistry, and DFT calculations.

Synthesis and photophysical properties of novel butterfly-shaped blue emitters based on pyrene

Using 1,3,5,9-tetrabromo-7-tert-butylpyrene as the bromide precursor, a series of novel butterfly-shaped 1,3,5,9-tetraaryl substituted pyrene derivatives were synthesized by the Suzuki-Miyaura cross-coupling reaction. Their thermal, photophysical, electrochemical and related properties were systematically investigated. All compounds were found to exhibit high thermal stabilities with decomposition temperatures (Td) of up to 300 °C. All compounds show highly blue fluorescence emissions in the spectral region of 412-469 nm in solution (Φf: 0.45-0.92) and 410-470 nm in the solid- state (Φf: 0.48-0.75). It is noteworthy that these butterfly-shaped pyrenes 4 possess low-lying HOMO levels ranging from -4.76 to -5.93 eV, which make them promising candidates in OLED applications.

Solvent effect and fluorescence response of the 7-tert-butylpyrene-dipicolylamine linkage for the selective and sensitive response toward Zn(II) and Cd(II) ions

The different binding behaviour of 7-tert-butylpyrene based chemosensors bearing dipicolylamine (Dpa) linkages at the 1,3-positions was investigated in various solvents for the sensing of Zn(II) and Cd(II).The potential mono-chelating ligand L1 follows the same binding pattern in both THF and methanol–water solvent systems, exhibiting higher selectivity and sensitivity for Cd(II) over Zn(II) mainly in THF solvent system. The potential bis-chelate ligand L2 can selectively bind both Zn(II) and Cd(II) in a 1:1 ratio in THF, whereas in methanol–water (7:3) at pH = 7.0; a 1:2 binding ratio was observed. In THF, two sites of ligand L2 can only selectively and sensitively bind one Zn(II) or Cd(II). The different complexation behaviour of L1 and L2 in different solvents were studied by means of fluorescence spectra and 1H-NMR titration experiments in the presence of Zn(II) and Cd(II).

Regioselective Substitution at the 1,3- and 6,8-Positions of Pyrene for the Construction of Small Dipolar Molecules

This article presents a novel asymmetrical functionalization strategy for the construction of dipolar molecules via efficient regioselective functionalization along the Z-axis of pyrene at both the 1,3- and 6,8-positions. Three asymmetrically substituted 1,3-diphenyl-6,8-R-disubsituted pyrenes were fully characterized by X-ray crystallography, photophysical properties, electrochemistry, and density functional theory calculations.

Positive and negative allosteric effects of thiacalix[4]arene-based receptors having urea and crown-ether moieties

Heteroditopic receptors (4a–e) based on a thiacalix[4]arene in the 1,3-alternate conformation, which have two urea moieties linking various phenyl groups substituted with either electron-donating or -withdrawing groups at their m-, or p-positions with a crown-ether moiety at the opposite side of the thiacalix[4]arene cavity, have been synthesized. The two examples with p-CH3– (4b) and p-NO2-substituted (4e) phenyl groups have been characterized by X-ray crystallography. The binding properties of receptor 4e were investigated by means of 1H NMR spectroscopic and absorption titration experiments in CHCl3–DMSO (10 : 1, v/v) solution in the presence of K+ ions and various anions. Interestingly, it was found that receptor 4e, which possesses two p-nitrophenyl ureido moieties, can complex most efficiently in the urea cavity or the crown-ether moiety; and the plausible allosteric effect of receptor 4e was also studied.

Iron(III) bromide catalyzed bromination of 2-tert-butylpyrene and corresponding position-dependent aryl-functionalized pyrene derivatives

The present work probes the bromination mechanism of 2-tert-butylpyrene (1), which regioselectively affords mono-, di-, tri- and tetra-bromopyrenes, by theoretical calculation and detailed experimental methods. The bromine atom may be directed to the K-region (positions 5- and 9-) instead of the more reactive 6- and 8-positions in the presence of iron powder. In this process, FeBr3 plays a significant role to release steric hindrance or lower the activation energy of the rearrangement. The intermediate bromopyrene derivatives were isolated and confirmed by 1H NMR spectrometry, mass spectroscopy and elemental analysis. Further evidence on substitution position originated from a series of aryl substituted pyrene derivatives, which were obtained from the corresponding bromopyrenes on reaction with 4-methoxy-phenylboronic acid by a Suzuki–Miyaura cross-coupling reaction. All position-dependent aryl-functionalized pyrene derivatives are characterized by single X-ray diffraction, 1H/13C NMR, FT-IR and MS, and offered straightforward evidence to support our conclusion. Furthermore, the photophysical properties of a series of compounds were confirmed by fluorescence and absorption, as well as by fluorescence lifetime measurements.

Synthesis and evaluation of a novel ionophore based on a thiacalix[4]arene derivative bearing imidazole units

O-Alkylation of the flexible thiacalix[4]arene 1 with 2-chloromethyl-1-methyl-1H-imidazole 2 in the presence of Na2CO3 or K2CO3 afforded mono-O-alkylation product 3 in 29–51% yield, along with recovery of the starting compound. In contrast, the same reaction in the presence of Cs2CO3 gave only one pure stereoisomer, namely 1,3-alternate-4; other possible isomers were not observed. Alkali metal salts such as Na2CO3 and Cs2CO3 can play an important role in the conformer distribution via a template effect. The conformations of the receptors, mono-O-alkylation product 3 and that of 1,3-alternate-4, have been confirmed by X-ray crystallography. Furthermore, the complexation properties of the receptor 1,3-alternate-4 toward selected alkali/transition metal cations are reported. The two-phase solvent extraction data indicated that 1,3-alternate-4 exhibited a stronger extraction efficiency for transition metals over alkali metals. The dichromate anion extraction ability of 1,3-alternate-4 showed that it could serve as an efficient extractor of HCr2O7−/Cr2O72− anions at low pH.

A study of anion binding behaviour of 1,3-alternate thiacalix[4]arene–based receptors bearing urea moieties

Three novel thiacalix[4]arene receptors 4a–c each with a 1,3-alternate conformation and possessing two urea moieties linking various phenyl groups substituted with either para electron-donating or -withdrawing groups have been synthesized. The binding properties of these receptors were investigated by means of 1H NMR spectroscopy and UV-vis absorption titration experiments using various anions. The structures and complexation energies were also studied by density functional theory (DFT) methods. The results suggested that receptor 4c, which possesses two p-(trifluoromethyl)phenyl ureido moieties, can complex most efficiently in the urea cavity and exhibits high selectivity towards F− and AcO− ions.

A Rare and Exclusive Endoperoxide Photoproduct Derived from a Thiacalix[4]arene Crown-Shaped Derivative Bearing a 9,10-Substituted Anthracene Moiety

A rare and exclusive endoperoxide photoproduct was quantitatively obtained from a thiacalix[4]arene crown-shaped derivative upon irradiation at λ=365 nm; the structure was unambiguously confirmed by (1) H/(13) C NMR spectroscopy and X-ray crystallography. The prerequisites for the formation of the endoperoxide photoproduct have also been discussed. Furthermore, the photochemical reaction rate could be greatly enhanced in the presence of the thiacalix[4]arene platform because it served as a host to capture oxygen.