Takanobu Sanji

Herein, we report the synthesis of a new type of poly(aryleneethynylene) (PAE) comprising electron-deficient tetrafluoroarene units in the π-conjugated backbone and water-solubilizing oligoether (OE) side chains. The fluorinated PAEs were synthesized using a transition-metal-free polymerization system promoted by fluoride anions. Long OE side chains typically retard the polymerization. However, this is resolved by using a tBuOK initiator with a large excess of cryptand-222. The present fluorinated PAEs display spectrophotometrically sufficient solubility in water, high fluorescence quantum yields, and reductive fluorescence quenching by arylamines.

Chiral crystalline compounds of the series of [Ln(α₂-P₂W₁₇O₆₁)₂]^17– polyanions embracing nearly all the lanthanide (Ln) ions were successfully isolated using Pro (proline) as a chiral director. In each compound, the polyanion and Pro were associated through a stereoselective interaction involving N(H)···O hydrogen bonding. ³¹P NMR and circular dichroism studies revealed the induction of chirality by Pro in the racemic aqueous systems of the [Ln(α₂-P₂W₁₇O₆₁)₂]^17– polyanions, i.e., the Pfeiffer effect. Mechanistically, this racemization was regulated by competitive enantiomeric interactions between the l-/d-Pro and l-/d-polyanions, with only one racemization route (the on-site rotation of the [α₂-P₂W₁₇O₆₁)]^10– unit) observed, independent of the nature of Ln.

The design and synthesis of asymmetric AB-type monomers, 2-polyfluorophenyl-5-trimethylsilylthiophenes, and the transition-metal-free polymerization promoted by fluoride anions are described. The polymerization depended on the substitution position and also the number of fluorines on the phenyl groups; i.e., a 3,4,5-trifluorophenyl-substituted monomer proceeded the polymerization by a catalytic amount of potassium t-butoxide in the presence of cryptand[2.2.2] with controlled molecular weights and relatively low polydispersity indexes, but 2,4,6- and 2,3,4-trifluoro-substituted and also 3,4-difluoro-substituted monomers did not. The NMR spectra of the resulting polymers were consistent with a highly regulated structure for the polymer main chain, indicating that the polymerization process itself must be highly regioselective under these conditions. By using the polymerization, end-capping and block copolymerization with high fidelity were also demonstrated.

The synthesis and photophysical properties of a series of phenyleneethynylenes containing a main group element moiety of B, Si, or P on the side chain as a simple model are reported. The HOMO‐LUMO energy levels are significantly altered due to a rise of the HOMO level (P) or a lowering of the LUMO level (B and PO) compared with the parent phenyleneethynylene, which is also supported by density functional theory calculations. In addition, the optical properties of boron‐ and phosphorus‐containing π systems are dramatically changed by the coordination of fluoride ion and oxidation, respectively.

For the racemisation, the [Ln(α-PW₁₁O₃₉)₂]¹¹⁻polyanion with light Ln experienced the ‘on-site rotation’ mechanism, while the [Ln(α-PW₁₁O₃₉)₂]¹¹⁻polyanion with heavy Ln followed the “dissociation–association” mechanism.

A transition-metal-free polymerization of an AB-type monomer for the synthesis of well-defined poly(p-phenyleneethynylene)s is described. The polymerization of 1-pentafluorophenylethynyl-4-[(trimethylsilyl)ethynyl]benzene with a catalytic amount of tetrabutylammonium fluoride or potassium t-butoxide in the presence of cryptand[2.2.2] affords polymers within a few minutes. When monitoring the polymerization, the molecular weight as a function of monomer conversion shows a linear relationship, where the polydispersity indexes are around 1.6. The polymerization proceeds predominantly via intramolecular fluoride anion transfer to the polymer end. End capping of the active polymerization end is also demonstrated.

We present an alternative approach to fabricating hexagonally arranged nanodot arrays of various metals by seed-mediated electroless plating with a cylinder-forming block copolymer thin film, PEO- b -PMA(Az), as a scaffold. Metal ions were selectively incorporated into PEO cylinders, followed by their reduction to metal and the etching of the scaffold to obtain highly ordered seed arrays of Au, Pd, and Pt. Nanodot arrays of the target metals (Au, Ag, and Ni) were selectively grown on the seed with their highly ordered arrangement by electroless plating. We studied the fabrication processes’ suitability for control of the nanodot array size, as well as the plasmonic properties thereof.