Interplay of Physical Structure and Photophysics for a Liquid Crystalline Polyfluorene

Grell, Martin; Bradley, Donal D. C.; Ungar, Goran; Hill, Jimmy; Whitehead, K. S.

doi:10.1021/ma990741o

Cited by 652 publications

(842 citation statements)

References 37 publications

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“…Fig. 3 depicts the fluorescence spectra of BE329 and GE108 at −250, −100, 0, and 100 • C. The spectra are blue-shifted under the sample heating and the vibronic structure is lost as reported for other polyfluorenes [2][3][4]. For GE108 the temperature dependence of the integrated spectra over the entire wavelength range (from 500 to 620 nm), reveals a monotonically decrease of the fluorescence intensity for increasing temperatures, consistent with the Fig.…”

Section: Mechanics Of Relaxation Processes (Solid-state Nmr)supporting

confidence: 83%

“…It has been observed that the optical and electrical properties of the electroluminescent materials are temperature dependent [1][2][3]. For polyfluorenes these properties were influenced by both the polymer relaxation involving chain segments as well as solid phase transitions when they crystallize or form liquid crystalline phases [3].…”

Section: Introductionmentioning

confidence: 99%

“…For polyfluorenes these properties were influenced by both the polymer relaxation involving chain segments as well as solid phase transitions when they crystallize or form liquid crystalline phases [3]. One of the reasons for the influence of the temperature on the electro-optical properties is the temperature dependence of the charge transport processes [4].…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Molecular relaxations in polyfluorene based cast films

Faria¹,

Cossiello

Atvars

et al. 2009

Synthetic Metals

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Section: Mechanics Of Relaxation Processes (Solid-state Nmr)supporting

confidence: 83%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Molecular relaxations in polyfluorene based cast films

Faria¹,

Cossiello

Atvars

et al. 2009

Synthetic Metals

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“…9 However, the fairly rigid fluorene-based π-conjugated polymers and copolymers tend to aggregate, which leads to low solubility, a marked decrease in the photoluminescence quantum yields, and a slight red shift in emission. [10][11][12] Any strategy that breaks up these polymer aggregates and improves their photophysical (particularly the emission quantum yield) properties is of great interest from the point of view of applications of this class of materials. Among the strategies that have been attempted are the incorporation of bulky substituents, 13 introduction of carbazole copolymer units, 14 the interaction with surfactants, [15][16][17] and most recently interaction with nanoparticle assemblies.…”

Section: Introductionmentioning

confidence: 99%

Interplay of Electrostatic and Hydrophobic Effects with Binding of Cationic Gemini Surfactants and a Conjugated Polyanion: Experimental and Molecular Modeling Studies

et al. 2007

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Understanding factors responsible for the fluorescence behavior of conjugated polyelectrolytes and modulation of their behavior are important for their application as functional materials. The interaction between the anionic poly{1,4-phenylene-[9,9-bis(4-phenoxy-butylsulfonate)]fluorene-2,7-diyl}copolymer (PBS-PFP) and cationic gemini surfactants R,ω-(C m H 2m+1 N + (CH 3 ) 2 ) 2 (CH 2 ) s (Br -) 2 (m-s-m; m ) 12, s ) 2, 3, 5, 6, 10, and 12) has been studied experimentally in aqueous solution. These surfactants are chosen to see whether molecular recognition and self-assembly occurs between the oppositely charged conjugated polyelectrolyte and gemini surfactant when the spacer length on the surfactant is similar to the intercharge separation on the polymer. Without surfactants, PBS-PFP exists as aggregates. These are broken up upon addition of gemini surfactants. However, as anticipated, the behavior strongly depends upon spacer length (s). Fluorescence measurements show three surfactant concentration regimes: At low concentrations (<2 × 10 -6 M) quenching occurs and is most marked with the small spacer 12-2-12; at intermediate concentrations (∼2 × 10 -6 -10 -3 M), fluorescence intensity is constant, with a 12-carbon spacer 12-12-12 showing the strongest fluorescence; above the critical micelle concentration (CMC; ∼10 -3 M) increases in emission intensity are seen in all cases and are largest with the intermediate spacers 12-5-12 and 12-6-12, where the spacer length most closely matches the distance between monomer units on the polymer. With longer spacer length surfactants, surface tension measurements for concentrations below the CMC reveal the presence of polymer-surfactant aggregates at the air-water interface, possibly reflecting increased hydrophobicity. Above the CMC, small-angle neutron scattering experiments for the 12-6-12 system show the presence of spherical aggregates, both for the pure surfactant and for polyelectrolyte/gemini mixtures. Molecular dynamics simulations help rationalize these observations and show that there is a very fine balance between electrostatic and hydrophobic interactions. With the shortest spacer 12-2-12, Coulombic interactions are dominant, while for the longest spacer 12-12-12 the driving force involves hydrophobic interactions. Qualitatively, with the intermediate 12-5-12 and 12-6-12 systems, the optimum balance is observed between Coulombic and hydrophobic interactions, explaining their strong fluorescence enhancement.

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“…[6] However, the blue emission from these materials is often unstable due to the formation of, e.g., ketone defects by oxidation of the methine bridges [7] or aggregate formation. [8,9] Another class of important potential blue emitters for OLEDs are small molecules based on imidazole. [10][11][12] 2,4,5-Triaryl-substituted imidazoles [4 (ref.…”

Section: Full Papermentioning

confidence: 99%

Blue Emission of a Soluble Poly(p‐phenylene) with a Cross‐Conjugated Bisimidazole‐Based Chromophore

Dierschke

Müllen

2007

Macro Chemistry & Physics

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A novel poly(p‐phenylene) (6) has been synthesized by a cruciform combination of a polyphenylene backbone with 2,2′‐(p‐phenylene)‐bis(4,5‐diphenylimidazole) (5) as an additional, orthogonal chromophore. Polymer 6 showed in solution and in the solid state, a blue‐green emission, which is obviously arising from the second bisimidazole‐based chromophore. UV‐Vis spectroscopy, and cyclic voltammetry revealed that the optical and electronic properties of 6 were fully determined by the incorporated 2,2′‐(1,4‐phenylene)bisimidazole structure. The bisimidazole unit led to high solubility and, despite the steric demand of the substituents, at the same time to the blue‐green emission of the poly(p‐phenylene) (6). In addition, the oxidation of 6 with potassium ferricyanide yielded a low bandgap polymer with a quinoid‐type structure and a bandgap of 1.6 eV.magnified image

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Interplay of Physical Structure and Photophysics for a Liquid Crystalline Polyfluorene

Cited by 652 publications

References 37 publications

Molecular relaxations in polyfluorene based cast films

Molecular relaxations in polyfluorene based cast films

Interplay of Electrostatic and Hydrophobic Effects with Binding of Cationic Gemini Surfactants and a Conjugated Polyanion: Experimental and Molecular Modeling Studies

Blue Emission of a Soluble Poly(p‐phenylene) with a Cross‐Conjugated Bisimidazole‐Based Chromophore

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