Anisotropic optical properties of aligned β-phase polyfluorene thin films

Endo, Toshiyuki; Kobayashi, Takashi; Nagase, Takashi; Naito, Hiroyoshi

doi:10.1016/j.tsf.2008.09.003

Cited by 14 publications

(18 citation statements)

References 17 publications

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“…The removal of β‐phase by chain motion would occur isotropically, that is, irrespective of the relative chain orientation, and thus the magnitude of the β‐phase absorption peak decreases equally for both parallel‐ and perpendicular polarized spectra. We note that this explanation is fully consistent with previous reports on oriented β‐phase PFO thin films, in which β‐phase was invariably introduced by postprocessing …”

Section: Resultssupporting

confidence: 92%

“…With respect to uniaxial order, direct orientation of PFO chains has been demonstrated via heating films into their thermotropic LC state on a variety of rubbed alignment layers including polyimide, poly( p ‐phenylenevinylene) and poly(3,4‐ethylenedioxythiophene)/polystyrene‐sulphonate . Friction‐transfer deposition and directional epitaxial crystallization have also been used.…”

Section: Introductionmentioning

confidence: 99%

“…Friction‐transfer deposition and directional epitaxial crystallization have also been used. The resulting film structure can be controlled to be predominantly glassy (after rapid quenching from the LC melt) or crystalline (after slow cooling from the LC melt or following friction transfer and epitaxial crystallization) and β‐phase chains can be subsequently generated by the usual post‐deposition treatments . Oriented PFO films prepared by these methods exhibit attractive properties such as improved hole mobility, enhanced optical gain, and anisotropic light emission with polarization ratios ≤50 achieved for LEDs based on oriented films .…”

Section: Introductionmentioning

confidence: 99%

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Interplay between solid state microstructure and photophysics for poly(9,9‐dioctylfluorene) within oriented polyethylene hosts

Perevedentsev

Aksel

Feldman

et al. 2014

J Polym Sci B Polym Phys

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We present a study of isotropic and uniaxially oriented binary blend films comprising 1 wt % of the conjugated polymer poly(9,9-dioctylfluorene) (PFO) dispersed in both ultrahigh molecular weight (UHMW) and linear-low-density (LLD) polyethylene (PE). Polarized absorption, fluorescence and Raman spectroscopy, scanning electron microscopy, and X-ray diffraction are used to characterize the samples before and after tensile deformation. Results show that blend films can be prepared with PFO chains adopting a combination of several distinct molecular conformations, namely glassy, crystalline, and the so-called b-phase, which directly influences the resulting optical properties. Both PFO concentration and drawing temperature strongly affect the alignment of PFO chains during the tensile drawing of the blend films. In both PE hosts, crystallization of PFO takes place during drawing; the resulting ordered chains show optimal optical anisotropy. Our results clarify the PFO microstructure in oriented blends with PE and the processing conditions required for achieving the maximal optical anisotropy. INTRODUCTION Molecular semiconductors are distinct from elemental and compound inorganic semiconductors in a number of important ways. One key feature is the option of low temperature processability that derives from relatively weak (typically van der Waals) intermolecular bonding; this allows the molecules in solid form to be readily separated in solution or melt and then reassembled in, for example, films on a device substrate. It is an enabling characteristic for printable/plastic electronics and has attracted major interest since the first report of solution-processed conjugated polymer light-emitting diodes (LEDs). 1 A consequence of relatively weak inter-molecular bonding is, however, that the solid-state microstructure can be sensitive to processing conditions and, therefore, complex. As a result, a range of amorphous/glassy, liquid-crystalline (LC) and (semi-)crystalline phases are found for many conjugated polymers.

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Section: Resultssupporting

confidence: 92%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Interplay between solid state microstructure and photophysics for poly(9,9‐dioctylfluorene) within oriented polyethylene hosts

Perevedentsev

Aksel

Feldman

et al. 2014

J Polym Sci B Polym Phys

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“…The detailed fabrication process for oriented ␤-phase F8 thin films with excellent dichroic ratios is described elsewhere. 26,27 The EA measurements used monochromatic light from a 500 W xenon lamp as the light source and a silicon photodiode as the photodetector. A function generator ͑NF, DF1906͒ and an ac power amplifier ͑NF, 4020͒ were utilized to apply an electric field modulated at a frequency of 1 kHz to the samples.…”

Section: Methodsmentioning

confidence: 99%

Electroabsorption study of ordered polyfluorene thin films: Origin of oscillatory structure near the bottom of the continuum state

et al. 2010

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The excited-state structure of ordered ͑␤-phase͒ poly͑9,9-dioctylfluorene͒ ͑F8͒ thin films has been investigated by electroabsorption ͑EA͒ spectroscopy. The EA spectra of a number of conjugated polymers, including disordered ͑glassy͒ F8, are well explained by a theoretical essential-state model, which consists of three characteristic excited states and the ground state ͓Y. Kawabe et al., Phys. Rev. B 44, 6530 ͑1991͔͒. However, it is found that the essential-state model fails to explain the EA spectrum of ␤-phase F8 because of the appearance of an oscillatory EA signal near the bottom of the continuum state. From the applied electric-field dependence and the directional dependence of the field and polarization of the light, it has been revealed that the oscillation results from several intrachain excited states, some of which are not observed in glassy F8 because of considerable inhomogeneous broadening. To reproduce the EA spectrum of ␤-phase F8 by a sum-over-states calculation, at least seven excited states, in addition to the ground state, have to be taken into account.

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“…It also exhibits high photoluminescence efficiency [5]. Usually, the -phase is obtained from the phase through thermal treatments and exposure to solvent vapors [4,6] or by using the action of low-quality solvents [7].…”

Section: Introductionmentioning

confidence: 99%