Jun Kawamata

A novel pyrene-based two-photon active fluorescent dye efficiently excited and emitting in the 'tissue optical window (650-1100 nm)'†

The development of two-photon (TP) active fluorophores remains an important issue. Dyes that can be excited and fluoresce efficiently in the tissue optical window (650-1100 nm) are especially in demand to maximize the underlying performance of two-photon fluorescence microscopy (TPFM) as an advanced optical technique. Ideally, such dyes would be compatible with the 1050 nm femtosecond fibre laser, which has recently been developed as an inexpensive excitation source to make the TPFM technique universal. In this work, we designed and synthesized a novel pyrene-based acceptor-π-acceptor (A-π-A) dye, PY, which exhibited outstanding properties such as bright fluorescence (λem = 650 nm and ΦFL = 0.80) and a large two-photon absorption cross-section (1100 GM (1 GM = 10-50 cm4 per photon per molecule) at 950 nm and 380 GM at 1050 nm) in the tissue optical window. In living mitochondria, PY provided more sensitive microscopic images than current dyes and showed great potential to be a building block of TP active fluorescent probes for the 1050 nm fibre laser. We believe that the exceptional properties of PY will be extended to other fluorescent probes through further chemical modification.

Dynamic behavior, electrochromism, and two-photon absorption of dicyanomethylenated quinacridone.

Molecular structures of dicyanomethylenated quinacridone (1) as a solid and in solution were examined on the basis of single-crystal X-ray structural analysis, temperature-dependent (1)H NMR in CD2Cl2, and theoretical calculations. Crystal 1 had a curved, butterfly-shaped molecular structure. Thermally activated flipping between the curved, butterfly-shaped structure and an armchair structure occurred in solution. Electrochemical reduction triggered a dynamic change from the curved, butterfly-shaped conformation in the neutral state to a planar conformation in the dianion state, which represented electrochromic behavior with electrochemical bistability. A large two-photon absorption cross section of compound 1 was observed in the resonance-enhancement region of 423 GM (1 GM = 1 × 10(-50) cm(4) s photon(-1) molecule(-1)) at 710 nm. Multiple donor-acceptor charge-transfer pathways of molecule 1 enhanced two-photon absorption.

The Formation of Organogels and Helical Nanofibers from Simple Organic Salts

Simple organic salts based on aniline-derived cations and D-tartrate anions formed organogels and helical nanofibers. The organic salt (p-fluoroanilinium)(D-tartrate) was found to generate an organogel despite the absence of a hydrophobic alkyl chain, whereas (p-iodoanilinium)(D-tartrate) formed helical nanofibers in braided ropelike structures through a rolling-up process. The helicity of these nanofibers could be reversed by changing the growth solvent. The driving forces responsible for the formation of the nanofibers were determined to be 1D Ouf8ffH⋅⋅⋅O(-) hydrogen-bonding interactions between D-tartrate anions and π stacking of anilinium cations, as well as steric hindrance between the hydrogen-bonded chains.

Incorporation of cationic electron donor of Ni-pyridyltetrathiafulvalene with anionic electron acceptor of polyoxometalate

A new salt-[Ni(II)(DMSO)(5)(TTFPy)](2)[α-SiW(12)O(40)] (1)-based on polyoxometalates was prepared by coordinating a cationic electron donor of pyridyltetrathiafulvalene (TTFPy) with Ni(II). Although the TTFPy molecule did not form a salt with the anionic α-[SiW(VI)(12)O(40)](4-) because of the weak charge-transfer (CT) interaction, the coordination of Ni with the pyridyl moiety permitted salt formation driven by electrostatic interaction, giving a single crystal of 1. Crystallographic analysis, UV-vis and IR spectroscopy and electrochemical characterization revealed that the fully oxidized α-[SiW(VI)(12)O(40)](4-) was crystallized with the neutral TTFPy moiety from the acetonitrile solution because of the low electron-withdrawing ability of α-[SiW(VI)(12)O(40)](4-), forming a brown-orange crystal. The crystal colour quickly turned to black by immersing in methanol, due to CT from TTF moiety to α-[SiW(VI)(12)O(40)](4-), which was caused by the solvent effect. Increase in the solvent acceptor number from 18.9 for acetonitrile to 41.3 for methanol resulted in the enhancement of the electron withdrawing ability of α-[SiW(VI)(12)O(40)](4-) by 0.317 V in methanol.

Large in-plane/out-of-plane anisotropic conduction in PEDOT-based hybrid films: lamellar assemblies structured by mono-layered nanosheets

Poly(3,4-ethylenedioxythiophene) (PEDOT) is a promising conductive polymer for electrical applications, and increases in its conductivity, transparency, stability, stiffness and strength have been explored. Herein, we demonstrate a facile fabrication method for a PEDOT film that exhibits large anisotropic conduction along in-plane directions. An aqueous solution of PEDOT added with polystyrene sulfonate (PSS) was mixed with an insulating oxide nanosheet based on montmorillonite (MMT) dispersed in aqueous media. Structural studies demonstrated it to be a hybrid film with a lamellar-like assembly that was structured with mono-layered sheets. In addition, an inhomogeneous mixture of pristine MMT (insulating) and PEDOT-rich (conductive) lamellar grains was proposed. The ratio between these two grains was controlled by tuning the content of the PEDOT:PSS solution in the initial mixing process. Increases in the content of PEDOT increased the electrical conductivity. This dependence is explained by a percolation model with random arrangements of PEDOT-rich conductive and insulating grains. The conductivity showed large anisotropy between in-plane and out-of-plane measurements. The ratio reached almost 105 and remained the same over a wide range of temperatures. The lamellar structure of the PEDOT and nanosheets is ascribed to the large anisotropy.