The Influence of the Molecular Weight on the Thermotropic Alignment and Self-Organized Structure Formation of Branched Side Chain Hairy-Rod Polyfluorene in Thin Films

Knaapila, Matti; Stepanyan, Roman; Lyons, Benjamin P.; Torkkeli, Mika; Hase, Thomas P. A.; Serimaa, Ritva; Güntner, R.; Seeck, O. H.; Scherf, Ullrich; Monkman, Andrew P.

doi:10.1021/ma0477403

Cited by 47 publications

(77 citation statements)

References 42 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…As described in our previous publication 15 , pure 29/68-PF2/6 shows two hexagonal GIXD patterns in the ͑ab0͒ plane rotated by 30°with respect to each other arising from types I and II. Pure Ir͑Fl 5 Py͒ 3 shows essentially one GIXD feature, a broad diffraction arc at 0.4 Å −1 , which we ascribe to the intermolecular distance between oligofluorene chains.…”

supporting

confidence: 63%

“…As the positions of the arcs agree with the q values of the hexagonal diffraction orders of pure PF2/6, they cannot arise from phase separated Ir͑Fl 5 Py͒ 3 . Reflections of types I and II but no arcs are distinguishable in unaligned film on quartz, 15 and it is noteworthy that the arcs are not due to the decreased alignment along the ͑00c͒ direction but indicate hexagonal crystallites uniformly distributed on the ͑ab0͒ plane. The systematic reduction of uniaxial alignment, seen in Fig.…”

mentioning

confidence: 91%

“…14 Low MW samples exhibit only a single nematic liquid crystal phase ͑n-LC and M n Ͻ M n * ͒ while high MW samples ͑M n Ͼ M n * ͒ include a distinctive thermotropic transition between this n-LC phase and a hexagonal crystalline phase. This threshold MW also marks sharp changes in both meridional alignment 15 and surface morphology. 16 In aligned films on rubbed polyimide ͑PI͒, the rigid PF2/6 lies on the substrate with the helical axes pointing along the rubbing direction ͑denoted z here͒.…”

mentioning

confidence: 93%

“…The differently oriented crystallite types are present both in uniaxially aligned and in-plane aligned films. 15 This indicates that ͑macroscopic͒ meridional and ͑surface preferential͒ equatorial alignment of PF2/6 crystallites are two distinct processes. PF2/6 has potential in thin-film device applications as a white light emitting diode made via "doping" with rubrene 19 or star-like tris-cyclometalated oligofluorenylpyridine iridium͑III͒ ͓Ir͑Fl x Py͒ 3 ͔ guests.…”

mentioning

confidence: 96%

See 3 more Smart Citations

Influence of star-like iridium complexes in the graphoepitaxy of polyfluorene thin films

et al. 2006

View full text Add to dashboard Cite

We report on the impact on the equatorial and meridional orientation in hairy-rod poly͓9,9-bis͑2-ethylhexyl͒-fluorene-2,7-diyl͔ thin films when blended with tris-cyclometalated oligo-fluorenylpyridine iridium͑III͒ complex. The presence of this transition-metal complex does not alter the underlying helical motif of the polymer chain or the hexagonal unit-cell intermolecular packing. However, systematic changes in the resulting texture patterning of the crystallites are observed. Crystallites with two preferred a-b orientations, so called type I and II and differing by 30 degrees, are superimposed on an isotropic background that is designated as type III. The extent of meridional alignment for all three is found to be similar. DOI: 10.1103/PhysRevB.74.214203 PACS number͑s͒: 61.10.Ϫi, 82.35.Lr, 81.07.Bc, 81.16.Dn Manipulating and controlling the molecular-level structure of functionalized polymers in bulk and at surfaces is central to the science and applications of these materials. Hairy-rod polymers 1 are one important example and, among those with -conjugated backbones 2 ͓e.g., poly͑p-phenylenes͒, 3 polyfluorenes ͑PFs͒, 4 and ladder derivatives 5 ͔, the nature of the main chain conformation and interchain packing are crucial factors in ultimately determining optical and transport properties. The structural characteristics at larger length scales are equally as important, and this has been the main emphasis in a number of recent studies. A classic example is the poly͑3-alkylthiophene͒ family 6 in which the extent of structural isomorphism or regioregularity strongly affects the internal crystallite structure 7 and the subsequent structural evolution when intercalated or doped. 8 Among PFs, important blue emitting polymers, even small differences in the molecular structure can influence the charge carrier mobility 9 and fluorescence. 10 Poly͓9,9-bis͑2-ethylhexyl͒-9H-fluorene-2,7-diyl͔ ͑or PF2/6͒ ͑Ref. 11͒ is a well-known helical PF polymer functionalized with branched alkyl side chains. PF2/6's optical properties 12 are relatively insensitive to either changes in the molecular weight ͑MW͒ or processing history, and so it is an excellent model system for studies of intermolecular self-organization. 13 However, this intermolecular assembly is affected by changes in the MW ͑or number averaged MW, M n ͒. In PF2/6, there is a threshold MW, M n * , at which there is a crossover in the phase behavior. 14 Low MW samples exhibit only a single nematic liquid crystal phase ͑n-LC and M n Ͻ M n * ͒ while high MW samples ͑M n Ͼ M n * ͒ include a distinctive thermotropic transition between this n-LC phase and a hexagonal crystalline phase. This threshold MW also marks sharp changes in both meridional alignment 15 and surface morphology. 16 In aligned films on rubbed polyimide ͑PI͒, the rigid PF2/6 lies on the substrate with the helical axes pointing along the rubbing direction ͑denoted z here͒. Consequently, meridional alignment leads to a large absorption and dispersion of the refractive index in the ͑xy0͒ plane along the z...

show abstract

supporting

confidence: 63%

mentioning

confidence: 91%

mentioning

confidence: 93%

mentioning

confidence: 96%

See 2 more Smart Citations

Influence of star-like iridium complexes in the graphoepitaxy of polyfluorene thin films

et al. 2006

View full text Add to dashboard Cite

show abstract

“…In this hexagonal phase the individual PF2/6 chains adopt a five-fold helix (5/2)with coherence lengths exceeding 50 nm. 15,17 Since the application of SCLC technique is based on the purity and crystallinity of a material, PF2/6 serves as a unique "test" case because of its structural properties.…”

Section: 17mentioning

confidence: 99%

Polyfluorene as a model system for space-charge-limited conduction

et al. 2007

View full text Add to dashboard Cite

Ethyl-hexyl substituted polyfluorene (PF) with its high level of molecular disorder can be described very well by one-carrier space-charge-limited conduction for a discrete set of trap levels with energy ∼ 0.5 eV above the valence band edge. Sweeping the bias above the trap-filling limit in the as-is polymer generates a new set of exponential traps, which is clearly seen in the density of states calculations. The trapped charges in the new set of traps have very long lifetimes and can be detrapped by photoexcitation. Thermal cycling the PF film to a crystalline phase prevents creation of additional traps at higher voltages.

show abstract

Influence of Molecular Weight on the Surface Morphology of Aligned, Branched Side-Chain Polyfluorene

et al. 2005

View full text Add to dashboard Cite

The Influence of the Molecular Weight on the Thermotropic Alignment and Self-Organized Structure Formation of Branched Side Chain Hairy-Rod Polyfluorene in Thin Films

Cited by 47 publications

References 42 publications

Influence of star-like iridium complexes in the graphoepitaxy of polyfluorene thin films

Influence of star-like iridium complexes in the graphoepitaxy of polyfluorene thin films

Polyfluorene as a model system for space-charge-limited conduction

Influence of Molecular Weight on the Surface Morphology of Aligned, Branched Side-Chain Polyfluorene

Contact Info

Product

Resources

About