Aggregation of Conjugated Polymers in Aromatic Solvent

Rahman, M. Habibur; Liao, Shao Ching; Chen, Hsin Lung; Chen, Jean Hong; Иванов, В. А.; Chu, Peter P.; Chen, Show An

doi:10.1021/la802526d

Cited by 36 publications

(46 citation statements)

References 45 publications

(107 reference statements)

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“…At the concentrations used in these NMR experiments, PF2/6 is known to aggregate in aromatic solvents, such as toluene. 17 Since it is difficult solely from NMR spectroscopy to rule out interchain aggregations with polyfluorenes, 15 we have studied the behavior of PF2/6 in chloroform solution using fluorescence spectroscopy, which gives direct information on any perturbations to the aromatic backbone arising from π-stacking or other effects. These experiments are not easy to perform in the same concentration range used in the NMR study due to inner filter and reabsorption effects.…”

Section: Table 1: Comparison Between 13 C Nmr Experimental Chemical Smentioning

confidence: 99%

“…16 Moreover, solvent can have a dramatic influence on the structure and aggregation behavior of PFs. 17 The study of the structural and electronic properties of polyfluorenes, both in solution and in solid state, is of key importance for the understanding of the properties of homologous polymer and oligomer systems, particularly in view of their applications in optoelectronic devices. Furthermore, the crystallinity and molecular packing of a polymer is related to a large extent to its backbone conformation.…”

Section: Introductionmentioning

confidence: 99%

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Conformational Studies of Poly(9,9-dialkylfluorene)s in Solution Using NMR Spectroscopy and Density Functional Theory Calculations

et al. 2009

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Relationships have been obtained between intermonomer torsional angle and NMR chemical shifts ((1)H and (13)C) for isolated chains of two of the most important poly(9,9-dialkylfluorenes), poly[9,9-bis(2-ethylhexyl)fluorene-2,7-diyl] (PF2/6) and the copolymer poly(9,9-dioctylfluorene-co-[2,1,3]benzothiadiazole-4,7-diyl) (F8BT), using DFT calculations. The correlations provide a model for NMR spectral data interpretation and the basis for analysis of conformational changes in poly(9,9-dialkylfluorene-2,7-diyl)s. The correlations obtained for PF2/6 indicate that the (13)C chemical shifts of the aromatic carbons close to the intermonomer connection (C1, C2, and C3) have minimum values at planar conformations (0 degrees and 180 degrees ) and maximum values at 90 degrees conformations. In contrast, the (1)H chemical shifts of the corresponding aromatic ortho protons (Ha and Hb) are greatest for planar conformations, and the minimum values are seen for 90 degrees conformations. For the F8BT copolymer, similar relationships are observed for the (1)H (Ha, Hb, and Hc) aromatic shifts. Considering the aromatic carbons of F8BT, the behavior of C2, C4, C5, and C6 is similar to that found for the PF2/6 carbons. However, C1 and C3 of the fluorene moiety behave differently with varying torsion angle. These are in close proximity to the fluorene-benzothiadiazole linkage and are markedly affected by interactions with the thiadiazole unit such that delta(C1) is a maximum for 180 degrees and a minimum for 0 degrees , whereas delta(C3) is a maximum for 0 degrees and minimum for 180 degrees. We have studied the (1)H and (13)C spectra of the two polymers at temperatures between -50 degrees C and +65 degrees C. The observed changes to higher or lower frequency in the aromatic resonances were analyzed using these theoretical relationships. Fluorescence studies on PF2/6 in chloroform solution suggest there are no significant interchain interactions under these conditions. This is supported by variable-temperature NMR results. Polymer-solvent and polymer intramolecular interactions were found to be present and influence all of the alkylic and one of the aromatic (1)H resonances (Hb). The detailed attribution of the (1)H and (13)C NMR spectra of the two polymers was made prior to the establishment of the relationships between torsion angle and NMR chemical shifts. This was carried out through DFT calculation of the (1)H and (13)C shielding constants of the monomers, coupled with distortionless enhancement by polarization transfer and heteronuclear correlation NMR spectra. Several DFT levels of calculation were tested for both optimization of structures and shielding constants calculation. The B3LYP/6-31G(d,p) method was found to perform well in both cases.

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Section: Table 1: Comparison Between 13 C Nmr Experimental Chemical Smentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Conformational Studies of Poly(9,9-dialkylfluorene)s in Solution Using NMR Spectroscopy and Density Functional Theory Calculations

et al. 2009

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“…2e) confirmed the prominent π-π stacking 23, 24 after 32 days’ room illumination. Freshly prepared PFluAnt solution showed the resonance peaks of anthracene moiety protons at 8.9, 8.7 and 8.6 ppm while the signal of fluorene ring proton appeared from 7.7 ppm to 8.0 ppm.…”

Section: Resultsmentioning

confidence: 63%

Observation of aggregation triggered by Resonance Energy Transfer (RET) induced intermolecular pairing force

Pan

Wang

et al. 2017

Sci Rep

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In this report, we showed the existence of RET induced intermolecular pairing force by comparing their fluorescence behaviors under room illumination vs standing in dark area for either PFluAnt solution or PFluAnt&PFOBT mixture. Their prominent emission attenuation under room illumination brought out the critical role of photo, i.e. RET induced intermolecular pairing force in induction of polymer aggregation. Constant UV-Vis absorption and fluorescence spectra in terms of both peak shapes and maximum wavelengths implied no chemical decomposition was involved. Recoverable fluorescence intensity, fluorescence lifetime as well as NMR spectra further exclude photo induced decomposition. The controllable on/off state of RET induced intermolecular pairing force was verified by the masking effect of outside PFluAnt solution which function as filter to block the excitation of inside PFluAnt and thus off the RET induced intermolecular pairing force. Theoretical calculation suggest that magnitude of RET induced intermolecular pairing force is on the same scale as that of van der Waals interaction. Although the absolute magnitude of RET induced intermolecular pairing force was not tunable, its effect can be magnified by intentionally turn it “on”, which was achieved by irradiance with 5 W desk lamp in this report.

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“…In a sharp contrast, the branched side chain PF2/6 manifests a system of locally isolated rigid chains which will overlap when c > c * 64. Furthermore, even though PF2/6 shows a sign for aggregation at ‐20 °C in 5‐50 mg/mL toluene79 the β ‐phase is never reported for it. An apparent question is where in between there is a transition from one behaviour to another.…”

Section: Molecular Parameters To Control Structure and Photophysicmentioning

confidence: 96%

Methods for Controlling Structure and Photophysical Properties in Polyfluorene Solutions and Gels

2013

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Knowledge of the phase behavior of polyfluorene solutions and gels has expanded tremendously in recent years. The relationship between the structure formation and photophysics is known at the quantitative level. The factors which we understand control these relationships include virtually all important materials parameters such as solvent quality, side chain branching, side chain length, molecular weight, thermal history and myriad functionalizations. This review describes advances in controlling structure and photophysical properties in polyfluorene solutions and gels. It discusses the demarcation lines between solutions, gels, and macrophase separation in conjugated polymers and reviews essential solid state properties needed for understanding of solutions. It gives an insight into polyfluorene and polyfluorene beta phase in solutions and gels and describes all the structural levels in solvent matrices, ranging from intramolecular structures to the diverse aggregate classes and network structures and agglomerates of these units. It goes on to describe the kinetics and thermodynamics of these structures. It details the manifold molecular parameters used in their control and continues with the molecular confinement and touches on permanently cross-linked networks. Particular focus is placed on the experimental results of archetypical polyfluorenes and solvent matrices and connection between structure and photonics. A connection is also made to the mean field type theories of hairy-rod like polymers. This altogether allows generalizations and provides a guideline for materials scientists, synthetic chemists and device engineers as well, for this important class of semiconductor, luminescent polymers.

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Aggregation of Conjugated Polymers in Aromatic Solvent

Cited by 36 publications

References 45 publications

Conformational Studies of Poly(9,9-dialkylfluorene)s in Solution Using NMR Spectroscopy and Density Functional Theory Calculations

Conformational Studies of Poly(9,9-dialkylfluorene)s in Solution Using NMR Spectroscopy and Density Functional Theory Calculations

Observation of aggregation triggered by Resonance Energy Transfer (RET) induced intermolecular pairing force

Methods for Controlling Structure and Photophysical Properties in Polyfluorene Solutions and Gels

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