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  Chiroptical properties of chiral substituted polyfluorenes

Oda, M., Nothofer, H. G., Scherf, U., Sunjic, V., Richter, D., Regenstein, W., et al. (2002). Chiroptical properties of chiral substituted polyfluorenes. Macromolecules, 35(18), 6792-6798. doi:10.1021/ma020630g.

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 Creators:
Oda, M.1, Author              
Nothofer, H. G.1, Author              
Scherf, Ullrich2, Author              
Sunjic, V., Author
Richter, D.3, Author              
Regenstein, W., Author
Neher, Dieter4, Author              
Affiliations:
1Univ Potsdam, Inst Phys, D-14469 Potsdam, Germany, ou_persistent22              
2Univ Potsdam, Inst Chem, D-14476 Golm, Germany, ou_persistent22              
3MPI for Polymer Research, Max Planck Society, ou_1309545              
4Univ Potsdam, Inst Phys & Astron, D-14476 Potsdam, Germany, ou_persistent22              

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 Abstract: Liquid-crystalline polyfluorene (PF) homopolymers substituted with chiral alkyl side chains were synthesized, and their chiroptical properties in the solid state were investigated by means of circular dichroism (CD), circularly polarized photoluminescence (CPPL), and circularly polarized electroluminescence (CPEL) measurements. Polarization-selective scattering of light is shown to cause artifacts in the circularly polarized absorption and emission spectra in the wavelength range near or above the absorption edge, and a measurement scheme to avoid these is presented. For all derivatives, significant chiroptical effects appeared only after the solid layers have been annealed at elevated temperatures, preferably into the liquid-crystalline state of the polymer. The largest anisotropy factors were measured for a polyfluorene substituted with chiral (R)-2-ethylhexyl side chains, yielding absolute values of up to 0.28 for CPPL and up to 0.25 for CPEL. These are among the highest ever reported for a chiral conjugated polymer. Anisotropy factors for CD, CPEL, and CPPL were consistently found to follow an "odd-even effect" concerning the position of the chiral center in the alkyl side chain. If the chiral center is placed close to the polymer backbone, the CD is dominated by one peak with its maximum close to the maximum of the pi-pi* absorption band. This indicates that the chiroptical. properties are most probably caused by intrachain effects rather than by pure interchain exciton coupling. This interpretation is supported by the results of time-dependent Hartree-Fock calculations for the isolated fluorene dimer and trimer. In both cases, the anisotropy factor depends strongly on the torsion angle between neighboring fluorene units. For the trimer, a maximum anisotropy factor of 0.25, close to the maximum values determined experimentally, is predicted for a torsion angle of ca. 105degrees. Both experimental and theoretical results indicate that the chiroptical properties of these chiral substituted polyfluorenes are mainly caused by a helical conformation of the conjugated polymer backbone.

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Language(s): eng - English
 Dates: 2002-08-27
 Publication Status: Published in print
 Pages: -
 Publishing info: -
 Table of Contents: -
 Rev. Type: No review
 Identifiers: eDoc: 28630
ISI: 000177688800011
DOI: 10.1021/ma020630g
 Degree: -

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Title: Macromolecules
  Other : Macromolecules
Source Genre: Journal
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Publ. Info: Washington, D.C. : American Chemical Society
Pages: - Volume / Issue: 35 (18) Sequence Number: - Start / End Page: 6792 - 6798 Identifier: ISSN: 0024-9297
CoNE: https://pure.mpg.de/cone/journals/resource/954925421108