@misc{oai:ir.soken.ac.jp:00000161,
 author = {北村, 千寿 and キタムラ, チトシ and KITAMURA, Chitoshi},
 month = {2016-02-17, 2016-02-17},
 note = {In the field of materials science, band structure engineering has become important since the bandgap is one of the most important factors controlling physical properties.  Especially, the search for polymers that possess narrow bandgaps is a current tonic because such polymers are expected to be promising candidates for intrinsic organic conductors and nonlinear optical devices.  Therefore, it is important to create new types of narrow-bandgap polymers and to examine the factors controlling bandgaps for further understanding the narrow-bandgap systems.  From these viewpoints, in Chapter 1, the discovery of narrow-bandgap polymers and the pathway of the research are overlooked and connected to a new molecular design.  By the analysis of factors controlling bandgaps, two molecular designs were extracted.  One is the copolymerization of aromatic and o-quinoid units.  Another is the alternation of strong electron-donating and electron-accepting moieties.  On the basis of them, periodic copolymers consisted of aromatic-donor (A:  thiophene and N-methylpyrrole) and ο-quinoid-acceptor (Q:  thieno[3, 4-b]pyrazine, quinoxaline, 2, 1, 3-benzothiadiazole, [1, 2, 5]thiadiazolo[3, 4-g]quinoxaline, benzo[1, 2-c;  4, 5-c']bis[1, 2, 5]-thiadiazole, pyrazino[2, 3-g]quinoxaline, and pyrazino[2, 3-b]quinoxaline) segments were planned to obtain new narrow bandgap systems.  A series of triheterocyclic monomers (A-Q-A) which were expected to polymerize by electrochemical oxidative coupling was designed to investigate the structure-property relationship.  The o-quinoid-acceptor heterocycles have no hydrogen atoms at peripheral positions, that would relieve the steric repulsion between adjacent segments.<br />  Chapter 2 deals with preparation and properties of the series of triheterocyclic monomers.  Since the properties of polymers are considered to correlate straightforwardly to those of monomers, the properties of monomers were examined in detail.  The monomers were synthesized through the coupling reaction of dihalo-substituted compounds with stannane compounds in the presence of a Pd(II) catalyst.  To estimate the properties of monomers roughly and to facilitate discussion later, MO calculations of each segment were carried out by the MNDO-PM3 method.  The results indicated that the HOMO level of N-methylpyrrole is higher than that of thiophene, and that the LUMO energies of ο-quinoid-acceptor heterocycles range widely.  Electronic spectra of the monomers with thiophene as aromatic-donor unit exhibited a trend that the monomer with ο-quinoid-acceptor unit whose LUMO level is lower has a longer absorption maximum.  On the other hand, the absorption bands of the monomers containing N-methylpyrrole displayed small blue shifts compared with the corresponding thiophene analogs against the speculation based on the MO calculations.  To solve this problem, X-ray analysis of some monomers with thiophene and  conformational analysis of the other monomers were performed.  They revealed that the molecules containing thiophene have almost coplanar conformations, while the molecules containing N-methylpyrrole have torsional geometries.  It was expected that the nonplanar conformations cause the reduction of effective delocalization.  Cyclic voltammetry measurements of the monomers displayed an irreversible oxidation wave and a reversible or quasi-reversible reduction wave, indicating amphoteric redox properties.  The difference between anodic and cathodic peak potentials depended on the LUMO levels of o-quinoid-acceptor heterocycles.<br />  Chapter 3 describes syntheses and properties of the variety of the corresponding polymers.  Electrochemical polymerization of the monomers stated above on Pt and ITO electrodes by a repetitive potential cycling method was attempted.  All the cyclic voltammograms but one showed the outlooks indicating the smooth growth of polymers deposited on an electrode over a period of polymerization.  The resulting polymers were relatively stable under ordinary conditions but insoluble to all the organic solvents even when longer alkyl chains were introduced.  Cyclic voltammograms of the polymers on a Pt disk electrode needed to be measured under certain strict conditions to gain clear reproducible voltammograms.  Most of the polymers containing thiophene units showed both p- and n- doping processes, indicating amphoteric redox properties similarly to the monomers.  The p-doping wave was broad and irreversible, while the n-doping wave was quasi-reversible (and sharp in the case of the polymers without alkyl substituents).  On the other hand, the polymers with N-methylpyrrole units hardly showed n-doping probably because the special conformations disturbed the tonic transport.  Some polymers exhibited characteristic waves possibly due to the charge trapping.  The small difference between the onset potentials of p- and n-doping, which corresponds to the bandgap in the conversion of V into eV, suggested that the resulting polymers had narrow bandgaps.  Electronic spectra of the polymers on an ITO-coated glass electrode were measured ex situ under control of potentials.  From the onset of the absorbance of neutral polymers, optical bandgaps were estimated.  As oxidized electrochemically, many polymers displayed characteristic electrochromic phenomena.  The bandgaps were a range of 0.5to 1.8 eV.  The value of 0.5 eV is one of the narrowest bandgaps reported so far.  Consequently, it was elucidated that the molecular design adopted in this thesis produced the new narrow-bandgap system effectively and that the structural modification tuned the bandgaps subtly., application/pdf, 総研大甲第181号},
 title = {Studies on New Narrow-Bandgap Polymers Composed of Aromatic-Donor and o-Quinoid-Acceptor Segments},
 year = {}
}