Hirotsugu Kawashima

Synthesis and Properties of Poly(Isothianaphthene Methine)s with Chiral Alkyl Chain

We synthesized poly(isothianaphthene methine)s with chiral alkyl chains in the substituent. Resultant polymers are soluble in THF and CHCl3. Structure of the polymers was characterized with FT-IR, FT-Raman, and UV-Vis-NIR optical absorption spectroscopy. They showed low-bandgap both in solution and in a form of film. Optical activity of the polymers was confirmed with optical rotatory dispersion. Doping effects on the polymer were also examined with UV-Vis-NIR spectroscopy and ESR measurement.

Intramolecular charge transfer (ICT) of a chiroptically active conjugated polymer showing green colour

A donor–acceptor type achiral monomer 4,7-bis(2,3-dihydrothieno[3,4-b]-1,4-dioxin-5-yl)-2,1,3-benzothiadiazole was synthesised and electrochemically polymerised in a cholesteric liquid crystalline (CLC) medium. This film exhibits a fingerprint pattern under the polarised optical microscopic observation. A possible mechanism of the fingerprint structure formation through a procedure of electrochemical polymerisation in a CLC medium is presented. The preparation of chiral polymer films even from achiral monomers is demonstrated. The film shows green colour in the reduced state and blue in the oxidised state. Changes in colour and CD signals of the film are repeatable with electrochemical oxidation and reduction. The presence of radical cations in the chiral environment, referred to as chiralions, distributed along chiral polymer chains is proposed.

Synthesis and optical properties of poly(phenylenethiophene)s bearing conjugated side chains

A series of π-conjugated polymers bearing conjugated side chain were prepared by Migita–Kosugi–Stille coupling polycondensation reaction. The polymers consisting of phenylene–thiophene (CCPTO), phenylene–isothianaphthene (CCPIO), and phenylene-3,4-ethylenedioxythiophene (CCPEO) conjugated backbones in the main chains showed optical absorption peaks in the same region, while fluorescence peak of CCPTO was at larger wavelengths compared with those of CCPIO and CCPEO. The polymers showed optical rotary dispersion, indicating the optically active substituents induced one-handed helicity to the polymers.

Synthesis and Properties of a Chiroptically Active Oligomer from 3,4-Ethylenedioxythiophene and (-)-Myrtenal

Oxidative polycondensation of 3,4-ethylenedioxythiophene and (–)-myrtenal was carried out with POCl3. A π-conjugated system thus constructed consists of aromatic and quinoidal alternating structure linked via methine groups. We examined iodine doping effect for the resultant material with electron spin resonance spectroscopy. Circular dichroism spectra in chloroform solution showed blue-shift with increase of iodine concentration. This result indicates that the doping process can tune chiroptical activity of the chiral π-conjugated system.