Synthesis, Structure, and Photophysical and Electrochemical Properties of a π-Stacked Polymer

Nakano, Tamaki; Yade, Tohru

doi:10.1021/ja037836x

Cited by 230 publications

(212 citation statements)

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“…Stable and regulated p-stacked structures in polymers have been realized for DNAs, 3 oligo(m-phenyleneethynylene)s, 4 oligomers consisting of alternating donor and acceptor monomeric units, 5,6 oligomers consisting of acceptor monomeric units in the main chain that interact with a low-molecular-weight donor molecule, 7 oligomers having perylene moieties in the main chain, 8,9 polymers consisting of cyclophane units, [10][11][12] a polymer of bezofulvene derivative, 13,14 and polymers of dibenzofulvene (DBF) and its derivatives (Chart 1). [15][16][17][18][19][20][21][22] In a DNA duplex, paired bases are regularly stacked inside the helical strand. In oligo (m-phenyleneethynylene)s, phenylene groups in the main chain closely overlap because of helical folding of the polymer chain.…”

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Synthesis, structure and function of π-stacked polymers

Nakano

2010

Polym J

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128

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Macromolecular conformation often has a significant effect on the properties of polymeric materials, and hence, conformational control in synthesizing a polymer is an important goal in polymer science. As a new conformational motif of vinyl polymers having side-chain p-electronic groups, we have introduced a 'p-stacked structure' in which side-chain chromophores are regularly stacked on top of each other and main-chain C-C bonds have a nearly all-trans, zigzag conformation. p-Stacked polymers can be prepared by vinyl polymerization of dibenzofulvene (DBF) and its derivatives. On the basis of the controlled structure, poly(DBF) and its derivatives exhibit unique photophysical and electronic properties as vinyl polymers. In addition, introduction of chirality to p-stacked polymers was also achieved. In this review, the synthesis of poly(DBF) and its derivatives and their structural analyses and properties are described. Polymer Journal (2010) 42, 103-123; doi:10.1038/pj.2009 Keywords: charge transport; chirality; dibenzofulvene; helix; photophysical properties; p-stacked structureIn designing functional organic materials with desired properties, spatial arrangement control of constituent molecules is an important factor because molecules in a regulated assembly often indicate properties different from those in solution or in gas phase because of specific intermolecular interactions. Effective molecular assembly control can be achieved by arrangement of functional molecules as a part of a polymer chain with a regulated conformation and configuration in which the polymer backbone functions as a structural template or scaffold. This is possible either by polymerizing functional molecules as monomers or by attaching functional molecules through a chemical reaction to a polymer chain. In the former case, the functional molecules to be aligned need to have a polymerizable moiety such as a vinyl group; they are a part of monomers and become constituents of a polymer chain as a part of monomeric units, typically as side-chain groups. The monomer structure itself may significantly contribute to the formation of a regulated polymer chain structure through intermolecular repulsion or attraction. An advantage of these polymer-based methods over other methodologies developed mainly for low-molecular-weight compounds based on the accumulation of relatively weak forces is that molecular orders formed along a polymer chain are generally stable due to covalent bonds. Moreover, using a polymer chain, a very tight or close packing of molecules (monomeric units), which is not plausible for the method based on weak intermolecular attractions, is possible when the enthalpy gain in covalent bond formation by polymerization or by polymer reaction outweighs the loss in free energy in packing molecules tightly into a small space around the polymer chain.Although these polymer-based methods generally require more synthetic efforts than intermolecular-force-based methods, a wider variety of molecular orders may be possible on the basis of re...

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Synthesis, structure and function of π-stacked polymers

Nakano

2010

Polym J

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101

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“…CR is directly connected to charge delocalization. Although there are several clear examples of CR band detection involving two aromatic molecules, [8][9][10][11][12][13][14] no systematic study has been reported on CR in regularly stacked, multiple aromtic groups in a molecule.The oligomers and the polymeric mixture having different degrees of polymerization (n in Scheme 1, left) were obtained by SEC separation from the anionic polymerization products of DBF prepared using MeLi as an initiator and EtI as a terminating reagent in tetrahydrofuran at À78 C. 4 The oligomers and the polymer were dissolved in dry CH 2 Cl 2 , and SbCl 5 in CH 2 Cl 2 was added to the solution. 15 The mixed solution showed a blue-green color, indicating the generation of radical cation.…”

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“…The oligomers and the polymeric mixture having different degrees of polymerization (n in Scheme 1, left) were obtained by SEC separation from the anionic polymerization products of DBF prepared using MeLi as an initiator and EtI as a terminating reagent in tetrahydrofuran at À78 C. 4 The oligomers and the polymer were dissolved in dry CH 2 Cl 2 , and SbCl 5 in CH 2 Cl 2 was added to the solution. 15 The mixed solution showed a blue-green color, indicating the generation of radical cation.…”

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confidence: 99%

“…2 We recently reported the synthesis and properties of poly(dibenzofulvene) (poly(DBF)) having a stable -stacked structure with the main-chain C-C bondings being all-trans and the side-chain fluorene chromophores being tightly stacked on top of each other. 3,4 Based on the findings that this polymer shows a high hole mobility in a bulk film form 5 and a reduced oxidation potential in electrochemical analysis, 4 it has been proposed that the stacked -electron systems of poly(DBF) may be an effective molecular wire. However, no direct information has been obtained on whether poly(DBF) delocalizes and transports charges.…”

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“…4 The oligomers and the polymer were dissolved in dry CH 2 Cl 2 , and SbCl 5 in CH 2 Cl 2 was added to the solution. 15 The mixed solution showed a blue-green color, indicating the generation of radical cation.…”

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Charge Delocalization over Stacked π-Electron Systems

Yade¹

2008

Chemistry Letters

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Cation radicals of oligomers and polymers of dibenzofulvene having a -stacked conformation showed broad absorption bands based on charge resonance in near IR region, which red-shifted with increasing degree of polymerization, indicating that charge delocalization takes place through multiple, stacked fluorene moieties.Polymers and oligomers that may transport injected charges are gathering attention as potential molecular wire.1 In this regard, various main-chain conjugating polymers have been designed. Apart from such long-range through-bond conjugating molecules, charge transport through stacked -electronic systems has been proposed as represented by the discussion on conduction behavior of DNAs. 2 We recently reported the synthesis and properties of poly(dibenzofulvene) (poly(DBF)) having a stable -stacked structure with the main-chain C-C bondings being all-trans and the side-chain fluorene chromophores being tightly stacked on top of each other.3,4 Based on the findings that this polymer shows a high hole mobility in a bulk film form 5 and a reduced oxidation potential in electrochemical analysis, 4 it has been proposed that the stacked -electron systems of poly(DBF) may be an effective molecular wire. However, no direct information has been obtained on whether poly(DBF) delocalizes and transports charges. Here, we report the chemical oxidation of DBF oligomers having two to eight monomeric units isolated by size-exclusion chromatography (SEC) and a polymeric mixture (n ! 9, M n 1890) and the observation of charge resonance (CR) 6 in multiple, stacked fluorene groups by near infra-red (NIR) absorption 7 spectroscopy. CR is directly connected to charge delocalization. Although there are several clear examples of CR band detection involving two aromatic molecules, [8][9][10][11][12][13][14] no systematic study has been reported on CR in regularly stacked, multiple aromtic groups in a molecule.The oligomers and the polymeric mixture having different degrees of polymerization (n in Scheme 1, left) were obtained by SEC separation from the anionic polymerization products of DBF prepared using MeLi as an initiator and EtI as a terminating reagent in tetrahydrofuran at À78 C. 4 The oligomers and the polymer were dissolved in dry CH 2 Cl 2 , and SbCl 5 in CH 2 Cl 2 was added to the solution. 15 The mixed solution showed a blue-green color, indicating the generation of radical cation. Figure 1 indicates the NIR absorption spectra of the oxidized oligo-and poly(DBF) samples and that of oxidized fluorene as a model of monomeric unit. In the spectrum of oxidized fluorene, a clear band was observed at 635 nm due to cation radical. 9 The spectra of the oxidized -stacked DBF oligomers and polymer indicated broad absorption bands due to CR in the near IR region in addition to the peak at 660-680 nm due to cation radical. Using the polymer sample (n ! 9, mixture), it was confirmed that the peak position of the near-IR band was not significantly affected by the sample concentration ([DBF unit] = 1:5 Â 10 À4 M, 5:9 Â 10 À5 M;...

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Asymmetric Polymerization

Ito¹,

Nozaki²

2010

Catalytic Asymmetric Synthesis

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Synthesis, Structure, and Photophysical and Electrochemical Properties of a π-Stacked Polymer

Cited by 230 publications

References 39 publications

Synthesis, structure and function of π-stacked polymers

Synthesis, structure and function of π-stacked polymers

Charge Delocalization over Stacked π-Electron Systems

Asymmetric Polymerization

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