The molecular parameters governing charge transport along a pi-stacked fluorene chain in poly(dib... more The molecular parameters governing charge transport along a pi-stacked fluorene chain in poly(dibenzofulvene) are studied by a joint experimental and theoretical approach involving high-resolution gas-phase photoelectron spectroscopy and quantum-mechanical methods. We specifically investigate the electronic couplings between fluorene moieties as well as the intramolecular reorganization energies, for both holes and electrons. Our results indicate that a pi-stacked fluorene chain favors hole transport over electron transport. The values for electronic couplings and reorganization energies estimated here are compared with those derived recently for pentacene.
The physical properties of a highly syndiotactic poly(vinyl alcohol) (PVA, diad syndiotacticity r... more The physical properties of a highly syndiotactic poly(vinyl alcohol) (PVA, diad syndiotacticity r 69% and a commercial, atactic PVA r 54% were examined. The highly syndiotactic PVA was derived from poly (vinyl acetate) prepared through the radical polymerization of vinyl acetate in (CF 3 ) 2 CHOH. The solubility, gelation behavior, melting point, and crystallization rate were drastically affected by the tacticity of the main chain. Some of the properties were measured using ®ber samples prepared by the gel spinning technique. The ®ber obtained from the syndiotactic PVA had a melting point of 2748C. This is the highest melting point reported for PVA. These effects of tacticity on the polymer properties are ascribed to the difference in intermolecular and/or intramolecular hydrogen bonding. A polymer chain with higher r content may form more regular and therefore more rigid hydrogen bonding between the polymer chains in the bulk sample. Such a detailed study on the effects of tacticity on the properties of PVA has not been reported so far. q
2-[4-(4'-Methoxyphenyl)phenoxylethyl, 3-[4-(4'-methoxyphenyl)phenoxylpropyl, 4-1444'-methoxypheny... more 2-[4-(4'-Methoxyphenyl)phenoxylethyl, 3-[4-(4'-methoxyphenyl)phenoxylpropyl, 4-1444'-methoxypheny1)phenoxyl butyl, 5-[4-(4'-methoxyphenyl)phenoxylpentyl, and 6-[4-(4'-methoxyphenyl)phenoxy] hexyl methacrylatee were synthesized and polymerized. Anionic polymerization of these monomers was carried out with tert-butylmagnesium bromide in toluene, chloroform, and tetrahydrofuran at low temperature, and radical polymerization was conducted with cY,a'-azobis(isobutyronitrile) in toluene at 60 "C. Highly isotactic (mm 90-97%) and syndiotactic (rr 79-86%) polymers were obtained by anionic polymerization in chloroform and tetrahydrofuran, respectively, and polymers rich in syndiotacticity (rr 5646% ) were obtained by radical polymerization. Thermal properties and liquid crystallinitiea of the polymers depended greatly on both the tacticity of the main chain and the length of the methylene chain (spacer) in the side group. These observations were interpreted in terms of zigzag (all-trans) and helical conformations of the main chain of syndio-and isotactic polymers, respectively, and the all-trans conformation of the spacer chain.
Optically active phenyl-2-pyridyl-o-tolylmethyl methacrylate (PPyoTMA) having various enantiomeri... more Optically active phenyl-2-pyridyl-o-tolylmethyl methacrylate (PPyoTMA) having various enantiomeric excesses was polymerized with diisopropyl peroxydicarbonate in toluene at 40 "C. Isotactic polymers were obtained. The polymers showed large optical rotations which are opposite in sign to the rotation of the starting monomer and the optical activity was higher than expected from the enantiomeric purity of the monomeric units in the polymer, indicating that a right-or left-handed helix was formed in excess from the steric effect of the chiral side group. Copolymerization of PPyoTMA with triphenylmethyl methacrylate (TrMA) also gave optically active, isotactic polymers; the phenyl-2-pyridyl-o-tolylmethyl group is also effective in inducing an excess of a single-handed helix consisting of TrMA monomeric sequences. Copolymerization with MMA gave atactic polymers showing much smaller optical activity than that of the copolymers with TrMA.
Dibenzofulvene (DBF) was polymerized using anionic initiators to afford a vinyl polymer. Oligo(DB... more Dibenzofulvene (DBF) was polymerized using anionic initiators to afford a vinyl polymer. Oligo(DBF)s having from two to eight side-chain fluorene moieties bearing different chain-terminal groups were isolated by preparative size-exclusion chromatography. The structures of the isolated oligomers were revealed by single-crystal X-ray and (1)H NMR analyses. Both in solution and in crystal, the in-chain fluorene moieties stacked on top of each other, while the terminal conformation varied depending on the terminal group. These conformational characteristics were supported by molecular mechanics and dynamics calculations. The oligomers and polymers indicated hypochromism and red shift in UV absorption spectra and exclusive excimer emission in fluorescence spectra. In addition, reduced oxidation potentials were observed for the oligomers in electrochemical analyses, which suggests charge delocalization over the pi-stacked electron systems. The photophysical and electrochemical effects increased with the chain length of the oligomers and leveled off around the chain length of an oligomer consisting of five fluorene units.
Page 1. Chem. Rev. 1994, 94, 349-372 349 Asymmetric Polymerization Yoshio Okamoto' and Tamak... more Page 1. Chem. Rev. 1994, 94, 349-372 349 Asymmetric Polymerization Yoshio Okamoto' and Tamaki Nakano Department of Applied Chemistry, Faculty of Engineering, Nagoya Universlty, Chikusa-ku, Nagoya 464-0 1, Japan ...
Asymmetric oligomerization of triphenylmethyl methacrylate (TrMA) was carried out with complexes ... more Asymmetric oligomerization of triphenylmethyl methacrylate (TrMA) was carried out with complexes of 9fluorenyllithium and chiral ligands in toluene at -78 "C, and the oligomers obtained were converted into methyl esters. The resulting oligo(methy1 methacry1ate)s were first fractionated by gel permeation chromatography in terms of degree of polymerization and further separated into diastereomers and optical isomers by high-performance liquid chromatography. The distribution of oligomers and the ratio of isomers in each oligomer gave important information on the mechanism of the asymmetric (helix sense selective) polymerization of TrMA. The reactivity of each oligomer anion depended greatly on its degree of polymerization and stereostructure. The oligomer anions whose asymmetric centers have R configuration in the system with the complex of 9-fluorenyllithium and (-)-sparteine and those of S configuration in the systems with (+)-(2S,3S)-2,3-dimethoxy-1,4bis(dimethy1amino)butane and (+)-(S)-1-(2-pyrrolidinyImethyl)pyrrolidine as chiral ligands predominantly propagated to a one-handed helical polymer. A stable helix starts at degree of polymerization 9 in the former system and at degree of polymerization 7 in the latter two systems. One helix turn seems to consist of three or four monomeric units. The main chain of the resulting polymer in the former system possessed RRR---absolute configuration and that in the latter systems SSS---, though both polymers are considered to be of the same helicity, P or M . These results indicate that the helicity of the polymer is not governed by the configuration of the main chain but by the chirality of the ligands.
The molecular parameters governing charge transport along a pi-stacked fluorene chain in poly(dib... more The molecular parameters governing charge transport along a pi-stacked fluorene chain in poly(dibenzofulvene) are studied by a joint experimental and theoretical approach involving high-resolution gas-phase photoelectron spectroscopy and quantum-mechanical methods. We specifically investigate the electronic couplings between fluorene moieties as well as the intramolecular reorganization energies, for both holes and electrons. Our results indicate that a pi-stacked fluorene chain favors hole transport over electron transport. The values for electronic couplings and reorganization energies estimated here are compared with those derived recently for pentacene.
The physical properties of a highly syndiotactic poly(vinyl alcohol) (PVA, diad syndiotacticity r... more The physical properties of a highly syndiotactic poly(vinyl alcohol) (PVA, diad syndiotacticity r 69% and a commercial, atactic PVA r 54% were examined. The highly syndiotactic PVA was derived from poly (vinyl acetate) prepared through the radical polymerization of vinyl acetate in (CF 3 ) 2 CHOH. The solubility, gelation behavior, melting point, and crystallization rate were drastically affected by the tacticity of the main chain. Some of the properties were measured using ®ber samples prepared by the gel spinning technique. The ®ber obtained from the syndiotactic PVA had a melting point of 2748C. This is the highest melting point reported for PVA. These effects of tacticity on the polymer properties are ascribed to the difference in intermolecular and/or intramolecular hydrogen bonding. A polymer chain with higher r content may form more regular and therefore more rigid hydrogen bonding between the polymer chains in the bulk sample. Such a detailed study on the effects of tacticity on the properties of PVA has not been reported so far. q
2-[4-(4'-Methoxyphenyl)phenoxylethyl, 3-[4-(4'-methoxyphenyl)phenoxylpropyl, 4-1444'-methoxypheny... more 2-[4-(4'-Methoxyphenyl)phenoxylethyl, 3-[4-(4'-methoxyphenyl)phenoxylpropyl, 4-1444'-methoxypheny1)phenoxyl butyl, 5-[4-(4'-methoxyphenyl)phenoxylpentyl, and 6-[4-(4'-methoxyphenyl)phenoxy] hexyl methacrylatee were synthesized and polymerized. Anionic polymerization of these monomers was carried out with tert-butylmagnesium bromide in toluene, chloroform, and tetrahydrofuran at low temperature, and radical polymerization was conducted with cY,a'-azobis(isobutyronitrile) in toluene at 60 "C. Highly isotactic (mm 90-97%) and syndiotactic (rr 79-86%) polymers were obtained by anionic polymerization in chloroform and tetrahydrofuran, respectively, and polymers rich in syndiotacticity (rr 5646% ) were obtained by radical polymerization. Thermal properties and liquid crystallinitiea of the polymers depended greatly on both the tacticity of the main chain and the length of the methylene chain (spacer) in the side group. These observations were interpreted in terms of zigzag (all-trans) and helical conformations of the main chain of syndio-and isotactic polymers, respectively, and the all-trans conformation of the spacer chain.
Optically active phenyl-2-pyridyl-o-tolylmethyl methacrylate (PPyoTMA) having various enantiomeri... more Optically active phenyl-2-pyridyl-o-tolylmethyl methacrylate (PPyoTMA) having various enantiomeric excesses was polymerized with diisopropyl peroxydicarbonate in toluene at 40 "C. Isotactic polymers were obtained. The polymers showed large optical rotations which are opposite in sign to the rotation of the starting monomer and the optical activity was higher than expected from the enantiomeric purity of the monomeric units in the polymer, indicating that a right-or left-handed helix was formed in excess from the steric effect of the chiral side group. Copolymerization of PPyoTMA with triphenylmethyl methacrylate (TrMA) also gave optically active, isotactic polymers; the phenyl-2-pyridyl-o-tolylmethyl group is also effective in inducing an excess of a single-handed helix consisting of TrMA monomeric sequences. Copolymerization with MMA gave atactic polymers showing much smaller optical activity than that of the copolymers with TrMA.
Dibenzofulvene (DBF) was polymerized using anionic initiators to afford a vinyl polymer. Oligo(DB... more Dibenzofulvene (DBF) was polymerized using anionic initiators to afford a vinyl polymer. Oligo(DBF)s having from two to eight side-chain fluorene moieties bearing different chain-terminal groups were isolated by preparative size-exclusion chromatography. The structures of the isolated oligomers were revealed by single-crystal X-ray and (1)H NMR analyses. Both in solution and in crystal, the in-chain fluorene moieties stacked on top of each other, while the terminal conformation varied depending on the terminal group. These conformational characteristics were supported by molecular mechanics and dynamics calculations. The oligomers and polymers indicated hypochromism and red shift in UV absorption spectra and exclusive excimer emission in fluorescence spectra. In addition, reduced oxidation potentials were observed for the oligomers in electrochemical analyses, which suggests charge delocalization over the pi-stacked electron systems. The photophysical and electrochemical effects increased with the chain length of the oligomers and leveled off around the chain length of an oligomer consisting of five fluorene units.
Page 1. Chem. Rev. 1994, 94, 349-372 349 Asymmetric Polymerization Yoshio Okamoto' and Tamak... more Page 1. Chem. Rev. 1994, 94, 349-372 349 Asymmetric Polymerization Yoshio Okamoto' and Tamaki Nakano Department of Applied Chemistry, Faculty of Engineering, Nagoya Universlty, Chikusa-ku, Nagoya 464-0 1, Japan ...
Asymmetric oligomerization of triphenylmethyl methacrylate (TrMA) was carried out with complexes ... more Asymmetric oligomerization of triphenylmethyl methacrylate (TrMA) was carried out with complexes of 9fluorenyllithium and chiral ligands in toluene at -78 "C, and the oligomers obtained were converted into methyl esters. The resulting oligo(methy1 methacry1ate)s were first fractionated by gel permeation chromatography in terms of degree of polymerization and further separated into diastereomers and optical isomers by high-performance liquid chromatography. The distribution of oligomers and the ratio of isomers in each oligomer gave important information on the mechanism of the asymmetric (helix sense selective) polymerization of TrMA. The reactivity of each oligomer anion depended greatly on its degree of polymerization and stereostructure. The oligomer anions whose asymmetric centers have R configuration in the system with the complex of 9-fluorenyllithium and (-)-sparteine and those of S configuration in the systems with (+)-(2S,3S)-2,3-dimethoxy-1,4bis(dimethy1amino)butane and (+)-(S)-1-(2-pyrrolidinyImethyl)pyrrolidine as chiral ligands predominantly propagated to a one-handed helical polymer. A stable helix starts at degree of polymerization 9 in the former system and at degree of polymerization 7 in the latter two systems. One helix turn seems to consist of three or four monomeric units. The main chain of the resulting polymer in the former system possessed RRR---absolute configuration and that in the latter systems SSS---, though both polymers are considered to be of the same helicity, P or M . These results indicate that the helicity of the polymer is not governed by the configuration of the main chain but by the chirality of the ligands.
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