1
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Effects of Charge Density on Photophysics and Aggregation Behavior of Anionic Fluorene-Arylene Conjugated Polyelectrolytes. Polymers (Basel) 2018; 10:polym10030258. [PMID: 30966293 PMCID: PMC6414976 DOI: 10.3390/polym10030258] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2018] [Revised: 02/23/2018] [Accepted: 02/26/2018] [Indexed: 01/19/2023] Open
Abstract
Three anionic fluorene-based alternating conjugated polyelectrolytes (CPEs) have been synthesized that have 9,9-bis(4-phenoxy-butylsulfonate) fluorene-2,7-diyl and 1,4-phenylene (PBS-PFP), 4,4′-biphenylene (PBS-PFP2), or 4,4″-p-terphenylene (PBS-PFP3) groups, and the effect of the length of the oligophenylene spacer on their aggregation and photophysics has been studied. All form metastable dispersions in water, but can be solubilized using methanol, acetonitrile, or dioxane as cosolvents. This leads to increases in their emission intensities and blue shifts in fluorescence maxima due to break-up of aggregates. In addition, the emission maximum shifts to the blue and the loss of vibronic structure are observed when the number of phenylene rings is increased. Debsity Functional Theory (DFT) calculations suggest that this is due to increasing conformational flexibility as the number of phenylene rings increases. This is supported by increasing amplitude in the fast component in the fluorescence decay. The nonionic surfactant n-dodecylpentaoxyethylene glycol ether (C12E5) also breaks up aggregates, as seen by changes in fluorescence intensity and maximum. However, the loss in vibrational structure is less pronounced in this case, possibly due to a more rigid environment in the mixed surfactant-CPE aggregates. Further information on the aggregates formed with C12E5 was obtained by electrical conductivity measurements, which showed an initial increase in specific conductivity upon addition of surfactants, while at higher surfactant/CPE molar ratios a plateau was observed. The specific conductance in the plateau region decreased in the order PBS-PFP3 < PBS-PFP2 < PBS-PFP, in agreement with the change in charge density on the CPE. The reverse process of aggregate formation has been studied by injecting small volumes of solutions of CPEs dissolved at the molecular level in a good solvent system (50% methanol-water) into the poor solvent, water. Aggregation was monitored by changes in both fluorescence and light scattering. The rate of aggregation increases with hydrophobicity and concentration of sodium chloride but is only weakly dependent on temperature.
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2
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Monteserín M, Burrows HD, Valente AJM, Pais AACC, Di Paolo RE, Maçanita AL, Tapia MJ. Fluorescence Enhancement of a Cationic Fluorene-Phenylene Conjugated Polyelectrolyte Induced by Nonionic n-Alkyl Polyoxyethylene Surfactants. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2017; 33:13350-13363. [PMID: 29112441 DOI: 10.1021/acs.langmuir.7b02818] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The modulation of conjugated polyelectrolyte fluorescence response by nonionic surfactants is dependent on the structures of the surfactant and polymer, polymer average molecular weight, and polyelectrolyte-surfactant interactions. In this paper, we study the effect of nonionic n-alkyl polyoxyethylene surfactants (CiEj) with different alkyl chain lengths (CiE5 with i = 6, 8, 10, and 12) and number of oxyethylene groups (C12Ej with j = 5, 7, and 9) on the photophysics and ionic conductivity of poly{[9,9-bis(6'-N,N,N-trimethylammonium)-hexyl]-2,7-fluorene-alt-1,4-phenylene}bromide (HTMA-PFP) in dimethyl sulfoxide-water 4% (v/v). Molecular dynamics simulations show that HTMA-PFP chains tend to approach as the simulation evolves. However, the minimum distance between the polymer centers of mass increases upon addition of the surfactant and grows with both the surfactant alkyl chain length and the number of oxyethylene groups, although there are no specific polymer-surfactant interactions. A significant increase in the polymer emission intensity has been observed at surfactant concentrations around their critical micelle concentrations (cmcs), which is attributed to polymer aggregate disruption. However, an increase in the solution conductivity for concentrations above the C12E5 cmc has only been observed for the HTMA-PFP/C12E5 system. The enhancement of fluorescence emission intensity and conductivity upon surfactant addition increases with polymer average molecular weights and seems to be controlled by the polymer-surfactant proximity, which is maximum for C10E5 and C12E5.
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Affiliation(s)
- María Monteserín
- Departamento de Química, Universidad de Burgos , Plaza Misael Bañuelos, Burgos 09001, Spain
| | - Hugh D Burrows
- Centro de Química de Coimbra (CQC), Department of Chemistry, University of Coimbra , 3004-535 Coimbra, Portugal
| | - Artur J M Valente
- Centro de Química de Coimbra (CQC), Department of Chemistry, University of Coimbra , 3004-535 Coimbra, Portugal
| | - A A C C Pais
- Centro de Química de Coimbra (CQC), Department of Chemistry, University of Coimbra , 3004-535 Coimbra, Portugal
| | - Roberto E Di Paolo
- Departamento de Engenharia Química e Biologica, Instituto Superior Técnico (IST) , Avenida Rovisco Pais, P1049-001 Lisboa, Portugal
| | - Antonio L Maçanita
- Departamento de Engenharia Química e Biologica, Instituto Superior Técnico (IST) , Avenida Rovisco Pais, P1049-001 Lisboa, Portugal
| | - María J Tapia
- Departamento de Química, Universidad de Burgos , Plaza Misael Bañuelos, Burgos 09001, Spain
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3
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Tsuchiya Y, Noguchi T, Yoshihara D, Roy B, Yamamoto T, Shinkai S. Conformation Control of a Conjugated Polymer through Complexation with Bile Acids Generates Its Novel Spectral and Morphological Properties. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2016; 32:12403-12412. [PMID: 27327101 DOI: 10.1021/acs.langmuir.6b01639] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Control of higher-order polymer structures attracts a great deal of interest for many researchers when they lead to the development of materials having various advanced functions. Among them, conjugated polymers that are useful as starting materials in the design of molecular wires are particularly attractive. However, an equilibrium existing between isolated chains and bundled aggregates is inevitable and has made their physical properties very complicated. As an attempt to simplify this situation, we previously reported that a polymer chain of a water-soluble polythiophene could be isolated through complexation with a helix-forming polysaccharide. More recently, a covalently self-threading polythiophene was reported, the main chain of which was physically protected from self-folding and chain-chain π-stacking. In this report, we wish to report a new strategy to isolate a water-soluble polythiophene and to control its higher-order structure by a supramolecular approach: that is, among a few bile acids, lithocholate can form stoichiometric complexes with cationic polythiophene to isolate the polymer chain, and the higher-order structure is changeable by the molar ratio. The optical and morphological studies have been thoroughly performed, and the resultant complex has been applied to the selective recognition of two AMP structural isomers.
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Affiliation(s)
- Youichi Tsuchiya
- Nanotechnology Laboratory, Institute of Systems, Information Technologies and Nanotechnologies (ISIT), Fukuoka Industry-Academia Symphonicity (FiaS), Kyudaishinmachi 4-1, Nishi-ku, Fukuoka 819-0388, Japan
| | | | - Daisuke Yoshihara
- Nanotechnology Laboratory, Institute of Systems, Information Technologies and Nanotechnologies (ISIT), Fukuoka Industry-Academia Symphonicity (FiaS), Kyudaishinmachi 4-1, Nishi-ku, Fukuoka 819-0388, Japan
| | | | - Tatsuhiro Yamamoto
- Nanotechnology Laboratory, Institute of Systems, Information Technologies and Nanotechnologies (ISIT), Fukuoka Industry-Academia Symphonicity (FiaS), Kyudaishinmachi 4-1, Nishi-ku, Fukuoka 819-0388, Japan
| | - Seiji Shinkai
- Nanotechnology Laboratory, Institute of Systems, Information Technologies and Nanotechnologies (ISIT), Fukuoka Industry-Academia Symphonicity (FiaS), Kyudaishinmachi 4-1, Nishi-ku, Fukuoka 819-0388, Japan
- Department of Nanoscience, Faculty of Engineering, Sojo University , Ikeda 4-22-1, Nishi-ku, Kumamoto 860-0082, Japan
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4
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Knaapila M, Stewart B, Costa T, Rogers SE, Pragana J, Fonseca SM, Valente AJM, Ramos ML, Murtinho D, Pereira JC, Mallavia R, Burrows HD. Incorporation of a Cationic Conjugated Polyelectrolyte CPE within an Aqueous Poly(vinyl alcohol) Sol. Macromolecules 2016. [DOI: 10.1021/acs.macromol.6b01895] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Affiliation(s)
- Matti Knaapila
- Department
of Physics, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
| | - Beverly Stewart
- Department
of Chemistry and Coimbra Chemistry Centre, University of Coimbra, 3004-535 Coimbra, Portugal
| | - Telma Costa
- Department
of Chemistry and Coimbra Chemistry Centre, University of Coimbra, 3004-535 Coimbra, Portugal
| | - Sarah E. Rogers
- Rutherford
Appleton
Laboratory, ISIS STFC, Chilton OX11 0QX, Oxon, U.K
| | - Joana Pragana
- Department
of Chemistry and Coimbra Chemistry Centre, University of Coimbra, 3004-535 Coimbra, Portugal
| | - Sofia M. Fonseca
- Department
of Chemistry and Coimbra Chemistry Centre, University of Coimbra, 3004-535 Coimbra, Portugal
| | - Artur J. M. Valente
- Department
of Chemistry and Coimbra Chemistry Centre, University of Coimbra, 3004-535 Coimbra, Portugal
| | - M. Luisa Ramos
- Department
of Chemistry and Coimbra Chemistry Centre, University of Coimbra, 3004-535 Coimbra, Portugal
| | - Dina Murtinho
- Department
of Chemistry and Coimbra Chemistry Centre, University of Coimbra, 3004-535 Coimbra, Portugal
| | - Jorge Costa Pereira
- Department
of Chemistry and Coimbra Chemistry Centre, University of Coimbra, 3004-535 Coimbra, Portugal
| | - Ricardo Mallavia
- Instituto
de Biología Molecular y Celular, Universidad Miquel Hernandez de Elche, Avda. de la Universidad s/n, 03202 Elche, Spain
| | - Hugh D. Burrows
- Department
of Chemistry and Coimbra Chemistry Centre, University of Coimbra, 3004-535 Coimbra, Portugal
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5
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Houston JE, Kraft M, Mooney I, Terry AE, Scherf U, Evans RC. Charge-Mediated Localization of Conjugated Polythiophenes in Zwitterionic Model Cell Membranes. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2016; 32:8141-8153. [PMID: 27434827 DOI: 10.1021/acs.langmuir.6b01828] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
The selective engineering of conjugated polyelectrolyte (CPE)-phospholipid interfaces is poised to play a key role in the design of advanced biomedical and biotechnological devices. Herein, we report a strategic study to investigate the relationship between the charge of the CPE side group and their association with zwitterionic phospholipid bilayers. The interaction of dipalmitoylphosphatidylcholine (DPPC) phospholipid vesicles with a series of poly(thiophene)s bearing zwitterionic, cationic, or anionic terminal groups (P3Zwit, P3TMAHT and P3Anionic, respectively) has been probed. Although all CPEs showed an affinity for the zwitterionic vesicles, the calculated partition coefficients determined using photoluminescence spectroscopy suggested preferential incorporation within the lipid bilayer in the order P3Zwit > P3Anionic ≫ P3TMAHT. The polarity probe Prodan was used to further qualify the position of the CPE inside the vesicle bilayers via Förster resonance energy transfer (FRET) studies. The varying proximity of the CPEs to Prodan was reflected in the Stern-Volmer quenching constants and decreased in the order P3Anionic > P3TMAHT ≫ P3Zwit. Dynamic light scattering measurements showed an increase in the hydrodynamic diameter of the DPPC vesicles upon addition of each poly(thiophene), but to the greatest extent for P3Anionic. Small-angle neutron scattering studies also revealed that P3Anionic specifically increased the thickness of the headgroup region of the phospholipid bilayer. Epifluorescence and atomic force microscopy imaging showed that P3TMAHT formed amorphous agglomerates on the vesicle surface, P3Zwit was buried throughout the bilayer, and P3Anionic formed a shell of protruding chains around the surface, which promoted vesicle fusion. The global data indicate three distinctive modes of interaction for the poly(thiophene)s within DPPC vesicles, whereby the nature of the association is ultimately controlled by the pendant charge group on each CPE chain. Our results suggest that charge-mediated self-assembly may provide a simple and effective route to design luminescent CPE probes capable of specific localization within phospholipid membranes.
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Affiliation(s)
- Judith E Houston
- School of Chemistry and CRANN, University of Dublin, Trinity College , College Green, Dublin 2, Ireland
| | - Mario Kraft
- Macromolecular Chemistry Group (Buwmakro) and Institute for Polymer Technology, Bergische Universität Wuppertal , Gauss-Str. 20, D-42119 Wuppertal, Germany
| | - Ian Mooney
- School of Chemistry and CRANN, University of Dublin, Trinity College , College Green, Dublin 2, Ireland
| | - Ann E Terry
- ISIS, STFC, Rutherford Appleton Laboratory, Didcot, Oxon OX11 0QX, U.K
| | - Ullrich Scherf
- Macromolecular Chemistry Group (Buwmakro) and Institute for Polymer Technology, Bergische Universität Wuppertal , Gauss-Str. 20, D-42119 Wuppertal, Germany
| | - Rachel C Evans
- School of Chemistry and CRANN, University of Dublin, Trinity College , College Green, Dublin 2, Ireland
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6
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Burrows HD, Costa T, Ramos ML, Valente AJM, Stewart B, Justino LLG, Almeida AIA, Catarina NL, Mallavia R, Knaapila M. Self-assembled systems of water soluble metal 8-hydroxyquinolates with surfactants and conjugated polyelectrolytes. Phys Chem Chem Phys 2016; 18:16629-40. [PMID: 26817700 DOI: 10.1039/c5cp07085f] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
We have studied the interaction of 8-hydroxyquinoline-5-sulfonate (8-HQS) with the metal ions Al(iii) and Zn(ii) in aqueous solution in the presence of tetraalkylammonium surfactants using UV/vis absorption, fluorescence, NMR spectroscopy and electrical conductivity measurements, complemented by DFT calculations and molecular dynamics (MD) simulations. Under appropriate conditions, complexes between 8-HQS and metal ions form rapidly, and have similar electronic, spectroscopic and photophysical properties to the corresponding metal quinolates, such as Alq3. These interact with the cationic surfactants, leading to marked increases in fluorescence intensity. However, significant differences are seen in the behavior of the two metal ions. With aluminium, a stable [Al(8-QS)3](3-) anion is formed, and interacts, predominantly through electrostatic interactions, with the surfactant, without disrupting the metal ion coordination sphere. In contrast, with Zn(ii), there is a competition between the metal ion and surfactants in the interaction with 8-HQS, although the [Zn(8-QS)2(H2O)2](2-) species is stable at appropriate pH and surfactant concentration. The studies are extended to systems with the conjugated polyelectrolyte (CPE) poly-(9,9-bis(6-N,N,N-trimethylammonium)hexyl)-fluorene-phenylene bromide (HTMA-PFP), which has a similar alkylammonium chain to the surfactants. Mixing metal salt, 8-HQS and HTMA-PFP in the presence of a nonionic surfactant leads to the formation of a metal complex/CPE supramolecular assembly between the conjugated polyelectrolyte and the metal/8-HQS complex, as demonstrated by electronic energy transfer. The potential of these systems in sensing, light harvesting, and electron injection/transport layers in organic semiconductor devices is discussed.
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Affiliation(s)
- Hugh D Burrows
- Centro de Química, Department of Chemistry, University of Coimbra, 3004-535 Coimbra, Portugal.
| | - Telma Costa
- Centro de Química, Department of Chemistry, University of Coimbra, 3004-535 Coimbra, Portugal.
| | - M Luisa Ramos
- Centro de Química, Department of Chemistry, University of Coimbra, 3004-535 Coimbra, Portugal.
| | - Artur J M Valente
- Centro de Química, Department of Chemistry, University of Coimbra, 3004-535 Coimbra, Portugal.
| | - Beverly Stewart
- Centro de Química, Department of Chemistry, University of Coimbra, 3004-535 Coimbra, Portugal.
| | - Licinia L G Justino
- Centro de Química, Department of Chemistry, University of Coimbra, 3004-535 Coimbra, Portugal.
| | - Aline I A Almeida
- Centro de Química, Department of Chemistry, University of Coimbra, 3004-535 Coimbra, Portugal.
| | - Nathanny Lessa Catarina
- Centro de Química, Department of Chemistry, University of Coimbra, 3004-535 Coimbra, Portugal.
| | - Ricardo Mallavia
- Instituto de Biología Molecular y Celular, Universidad Miguel Hernandez de Elche, Avda. de la Universidad s/n, 03202 Elche, Spain
| | - Matti Knaapila
- Department of Physics, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
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7
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Burrows HD, Valente AJ, Costa T, Stewart B, Tapia MJ, Scherf U. What conjugated polyelectrolytes tell us about aggregation in polyelectrolyte/surfactant systems. J Mol Liq 2015. [DOI: 10.1016/j.molliq.2015.04.012] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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8
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Tang Y, Liu Z, Zhu L, Han Y, Wang Y. Aggregation behavior of sodium lauryl ether sulfate with a positively bicharged organic salt and effects of the mixture on fluorescent properties of conjugated polyelectrolytes. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2015; 31:2104-2111. [PMID: 25641198 DOI: 10.1021/la504733q] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The aggregation behavior of anionic single-chain surfactant sodium lauryl ether sulfate containing three ether groups (SLE3S) with positively bicharged organic salt 1,2-bis(2-benzylammoniumethoxy)ethane dichloride (BEO) has been investigated in aqueous solution, and the effects of the BEO/SLE3S aggregate transitions on the fluorescent properties of anionic conjugated polyelectrolyte MPS-PPV with a larger molecular weight and cationic conjugated oligoelectrolyte DAB have been evaluated. Without BEO, SLE3S does not affect the fluorescent properties of MPS-PPV and only affects the fluorescent properties of DAB at a higher SLE3S concentration. With the addition of BEO, SLE3S and BEO form gemini-like surfactant (SLE3S)2-BEO. When the BEO/SLE3S molar ratio is fixed at 0.25, with increasing the BEO/SLE3S concentration, the BEO/SLE3S mixture forms large, loosely arranged aggregates and then transforms to closely packed spherical aggregates and finally to long thread-like micelles. The photoluminescence (PL) intensity of MPS-PPV varies with the morphologies of the BEO/SLE3S aggregates, while the PL intensity of DAB is almost independent of the aggregate morphologies. The results demonstrate that gemini-like surfactants formed through intermolecular interactions can effectively adjust the fluorescent properties of conjugated polyelectrolytes.
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Affiliation(s)
- Yongqiang Tang
- Key Laboratory of Colloid and Interface Science, Beijing National Laboratory for Molecular Sciences (BNLMS), Institute of Chemistry, Chinese Academy of Sciences , Beijing 100190, P. R. China
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9
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Koenen JM, Zhu X, Pan Z, Feng F, Yang J, Schanze KS. Enhanced Fluorescence Properties of Poly(phenylene ethynylene)-Conjugated Polyelectrolytes Designed to Avoid Aggregation. ACS Macro Lett 2014; 3:405-409. [PMID: 35590772 DOI: 10.1021/mz500067k] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
A new class of nonaggregating conjugated polyelectrolytes exhibits efficient fluorescence in aqueous solution. Analysis by optical spectroscopy and transmission electron microscopy reveals a unique structure-property correlation between oxygen substitution and aggregation.
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Affiliation(s)
- Jan-Moritz Koenen
- Department
of Chemistry and Center for Macromolecular Science and Engineering, University of Florida, P.O. Box 117200, Gainesville, Florida 32611-7200, United States
| | - Xuzhi Zhu
- Department
of Chemistry and Center for Macromolecular Science and Engineering, University of Florida, P.O. Box 117200, Gainesville, Florida 32611-7200, United States
| | - Zhenxing Pan
- Department
of Chemistry and Center for Macromolecular Science and Engineering, University of Florida, P.O. Box 117200, Gainesville, Florida 32611-7200, United States
| | - Fude Feng
- Baylor
College of Medicine, Texas Medical Center, Houston, Texas 77030, United States
| | - Jie Yang
- Department
of Chemistry and Center for Macromolecular Science and Engineering, University of Florida, P.O. Box 117200, Gainesville, Florida 32611-7200, United States
| | - Kirk S. Schanze
- Department
of Chemistry and Center for Macromolecular Science and Engineering, University of Florida, P.O. Box 117200, Gainesville, Florida 32611-7200, United States
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10
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Costa T, Marques AT, Seixas de Melo JS, Thomas AW, Garner LE, Scherf U, Bazan GC, Burrows HD. Self-assembly of poly{1,4-phenylene-[9,9-bis(4-phenoxy-butylsulfonate)]fluorene-2,7-diyl} with oppositely charged phenylenevinylene oligoelectrolytes. J Phys Chem B 2014; 118:613-23. [PMID: 24359025 DOI: 10.1021/jp409577y] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
The interaction of the water-soluble conjugated polyelectrolyte (CPE) poly{1,4-phenylene-[9,9-bis(4-phenoxy-butylsulfonate)]fluorene-2,7-diyl} (PBS-PFP) (degree of polymerization, DP, ∼3-6) with various concentrations of a homologous series of oppositely charged amphiphilic phenylenevinylene oligomers was investigated in water:dioxane mixtures and in aqueous micellar solutions of the non-ionic surfactant n-dodecylpentaoxyethylene glycol ether. The excellent spectral overlap between the CPE fluorescence and the conjugated oligoelectrolyte (COE) absorption indicates that energy transfer between these is a highly favored process, and can be tuned by changing the COE chain length. This is supported by time-resolved fluorescence data. The overall results provide support for different types of self-assembly, which are sensitive to the solvent environment and to the size of the phenylenevinylene oligoelectrolyte chain. It is suggested that large aggregates are formed in water:dioxane mixtures, while decorated core-shell structures are present in the surfactant solutions.
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Affiliation(s)
- Telma Costa
- Centro de Química de Coimbra, Department of Chemistry, University of Coimbra , 3004-535 Coimbra, Portugal
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11
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Costa T, Garner LE, Knaapila M, Thomas AW, Rogers SE, Bazan GC, Burrows HD. Aggregation properties of p-phenylene vinylene based conjugated oligoelectrolytes with surfactants. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2013; 29:10047-10058. [PMID: 23822142 DOI: 10.1021/la401871x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
The amphiphilic properties of conjugated oligoelectrolytes (COE) and their sensitivity to the polarity of their microenvironment lead to interesting aggregation behavior, in particular in their interaction with surfactants. Photoluminescence (PL) spectroscopy, liquid-phase atomic force microscopy, small-angle neutron scattering, small-angle X-ray scattering, and grazing-incidence X-ray diffraction were used to examine interactions between cationic p-phenylene vinylene based oligoelectrolytes and surfactants. These techniques indicate the formation of COE/surfactant aggregates in aqueous solution, and changes in the photophysical properties are observed when compared to pure aqueous solutions. We evaluate the effect of the charge of the surfactant polar headgroup, the size of the hydrophobic chain, and the role of counterions. At low COE concentrations (micromolar), it was found that these COEs display larger emission quantum efficiencies upon incorporation into micelles, along with marked blue-shifts of the PL spectra. This effect is most pronounced in the series of anionic surfactants, and the degree of blue shifts as a function of surfactant charge is as follows: cationic < nonionic < anionic surfactants. In anionic surfactants, such as sodium dodecyl sulfate (SDS), the PL spectra show vibronic resolution above the critical micelle concentration of the surfactant, suggesting more rigid structures. Scattering data indicate that in aqueous solutions, trimers appear as essentially 3-dimensional particles, while tetra- and pentamers form larger, cylindrical particles. When the molar ratio of nonionic C12E5 surfactant to 1,4-bis(4-{N,N-bis-[(N,N,N-trimethylammonium)hexyl]amino}-styryl)benzene tetraiodide (DSBNI) is close to one, the size of the formed DSBNI-C12E5 particles corresponds to the full coverage of individual oligomers. When these particles are transferred into thin films, they organize into a cubic in-plane pattern. If anionic SDS is added, the formed DSBNI-SDS particles are larger than expected for full surfactant coverage, and particles may thus contain several oligomers. This tendency is attributed to the merging of DSBNI oligomers due to the charge screening and, thus, reduced water solubility.
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Affiliation(s)
- Telma Costa
- Chemistry Department, University of Coimbra, Coimbra 3004-535, Portugal.
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12
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Inal S, Kölsch JD, Chiappisi L, Kraft M, Gutacker A, Janietz D, Scherf U, Gradzielski M, Laschewsky A, Neher D. Temperature-Regulated Fluorescence Characteristics of Supramolecular Assemblies Formed By a Smart Polymer and a Conjugated Polyelectrolyte. MACROMOL CHEM PHYS 2012. [DOI: 10.1002/macp.201200493] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
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13
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Formation and Characterization of Stable Fluorescent Complexes Between Neutral Conjugated Polymers and Cyclodextrins. J Fluoresc 2012; 23:171-80. [DOI: 10.1007/s10895-012-1130-5] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2012] [Accepted: 09/10/2012] [Indexed: 11/27/2022]
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14
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Marques AT, Burrows HD, Seixas de Melo JS, Valente AJM, Justino LLG, Scherf U, Fron E, Rocha S, Hofkens J, Snedden EW, Monkman AP. Spectroscopic properties, excitation, and electron transfer in an anionic water-soluble poly(fluorene-alt-phenylene)-perylenediimide copolymer. J Phys Chem B 2012; 116:7548-59. [PMID: 22554070 DOI: 10.1021/jp3000703] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
An anionic fluorene-phenylene poly{1,4-phenylene-[9,9-bis(4-phenoxy-butylsulfonate)]fluorene-2,7-diyl}-based copolymer containing on-chain perylenediimine (PDI) chromophoric units, PBS-PFP-PDI, was synthesized and its photophysical properties studied as aggregates and isolated chains in water and dioxane/water (1:1) solution. UV-vis and emission spectroscopy measurements, time-correlated single photon counting, and wide field imaging have been employed to investigate the excited-state behavior of the PBS-PFP-PDI copolymer, including the effect of environment on the energy and electron transfer to the on-chain PDI chromophore. Although the Förster overlap integral is favorable, no evidence is found for intramolecular singlet excitation energy transfer in isolated copolymer chains in solution. Fluorescence is suggested to involve an interchain process, thus revealing that isolated copolymer chains in solution do not undergo efficient intramolecular energy transfer. However, quenching of the PBS-PFP excited state by PDI is observed in aqueous media and ultrafast pump-probe studies in water or dioxane-water solutions show that electron transfer occurs from the phenylene-fluorene units to the PDI. The extent of electron transfer increases with aggregation, suggesting it is largely an interchain process. The interaction of the negatively charged PBS-PFP-PDI copolymer with the positively charged surfactant hexadecyltrimethylammonium bromide (CTAB) in solution has also been studied. The copolymer PBS-PFP-PDI aggregates with the surfactant already at concentrations below the critical micelle concentration (cmc) and the nonpolar environment allows intermolecular energy transfer, observed by the weak emission band located at 630 nm that is associated with the emission of the PDI chromophore. However, the fact that the PDI photoluminescence (PL) lifetime (~1.4 ns) obtained in the presence of CTAB is considerably shorter than that of the nonaggregated chromophore (~5.4 ns) suggests that even in this case there is considerable PL quenching, possibly through some charge transfer route. The increase of the PBS-PFP-PDI photoluminescence intensity at surfactant concentrations above the cmc indicates deaggregation of polyelectrolyte within the initially formed polyelectrolyte-surfactant aggregates.
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Affiliation(s)
- Ana T Marques
- Department of Chemistry, University of Coimbra, P3004-535 Coimbra, Portugal.
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15
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Valente A, Burrows H, Gomes J, Pereira R, Cerqueira D, Jiménez A, Burgos N, Morán C, Mallavia R, Filho G. Cellulose acetate-poly{[9,9-bis(6′-N,N,N-trimethylammonium)hexyl]fluorene-phenylene} bromide blends: Preparation, characterization and transport properties. REACT FUNCT POLYM 2012. [DOI: 10.1016/j.reactfunctpolym.2012.03.014] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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16
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Martelo L, Jiménez A, Valente AJM, Burrows HD, Marques AT, Forster M, Scherf U, Peltzer M, Fonseca SM. Incorporation of polyfluorenes into poly(lactic acid) films for sensor and optoelectronics applications. POLYM INT 2012. [DOI: 10.1002/pi.4176] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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17
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Marques AT, Pinto SMA, Monteiro CJP, Seixas de Melo JS, Burrows HD, Scherf U, Calvete MJF, Pereira MM. Energy transfer from fluorene-based conjugated polyelectrolytes to on-chain and self-assembled porphyrin units. ACTA ACUST UNITED AC 2012. [DOI: 10.1002/pola.25908] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
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18
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Aggregation behaviour of a water-soluble ammonium-functionalized polythiophene: Luminescence enhancement induced by bile-acid anions. POLYMER 2012. [DOI: 10.1016/j.polymer.2011.12.010] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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19
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Davies ML, Douglas P, Burrows HD, da Graça Miguel M, Douglas A. Effect of Aggregation on the Photophysical Properties of Three Fluorene–Phenylene-Based Cationic Conjugated Polyelectrolytes. J Phys Chem B 2011; 115:6885-92. [DOI: 10.1021/jp202446a] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Matthew L. Davies
- Chemistry Group, School of Engineering, Swansea University, Singleton Park Swansea, SA2 8PP, U.K
- Departamento de Química da Universidade de Coimbra, Rua Larga, 3004-535 Coimbra, Portugal
| | - Peter Douglas
- Chemistry Group, School of Engineering, Swansea University, Singleton Park Swansea, SA2 8PP, U.K
| | - Hugh D. Burrows
- Departamento de Química da Universidade de Coimbra, Rua Larga, 3004-535 Coimbra, Portugal
| | - Maria da Graça Miguel
- Departamento de Química da Universidade de Coimbra, Rua Larga, 3004-535 Coimbra, Portugal
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20
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Xu Z, Tsai H, Wang HL, Cotlet M. Solvent polarity effect on chain conformation, film morphology, and optical properties of a water-soluble conjugated polymer. J Phys Chem B 2011; 114:11746-52. [PMID: 20726542 DOI: 10.1021/jp105032y] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The solvent polarity effect on chain conformation, film morphology, and photophysical properties of a nonionic water-soluble conjugated polymer (WSCP), poly[2,5-bis(diethylaminetetraethylene glycol)phenylene vinylene] (DEATG-PPV) is investigated in detail. The combination of stationary absorption and photoluminescence (PL) spectroscopy, time-resolved PL spectroscopy, and fluorescence correlation spectroscopy methods enables us to probe the chain conformation of DEATG-PPV, down to the level of a single chain when working with extremely diluted solutions. The use of correlated atomic force microscopy and confocal fluorescence lifetime imaging microscopy measurements of drop-casted DEATG-PPV films reveals the intrinsic relationship between chain conformation, film morphology, and optical properties. Depending on solvent polarity, DEATG-PPV presents extended, coiled, and collapsed chain conformations in solutions, which lead to distinct morphology and optical properties in solid films. Our work presents a pathway to control and characterize the film morphologies of WSCPs toward the optimal performance of various optoelectronic devices.
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Affiliation(s)
- Zhihua Xu
- Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973, USA
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21
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Tapia M, Monteserín M, Costoyas A, Burrows H, Marques, A, Pais A, Valente A, Mallavia R, Scherf U, Pinazo A, Pérez L, Morán M. Effects of commercial non-ionic alkyl oxyethylene and ionic biocompatible arginine-based surfactants on the photophysical behaviour of several poly(fluorene-1,4-phenylene)s. J Mol Liq 2010. [DOI: 10.1016/j.molliq.2010.05.026] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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22
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Zhong S, Pochan DJ. Cryogenic Transmission Electron Microscopy for Direct Observation of Polymer and Small-Molecule Materials and Structures in Solution. POLYM REV 2010. [DOI: 10.1080/15583724.2010.493254] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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23
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Monteserín M, Burrows HD, Mallavia R, Di Paolo RE, Maçanita AL, Tapia MJ. How to change the aggregation in the DNA/surfactant/cationic conjugated polyelectrolyte system through the order of component addition: anionic versus neutral surfactants. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2010; 26:11705-11714. [PMID: 20518566 DOI: 10.1021/la1011764] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
The competitive interaction has been studied between double-stranded DNA (dsDNA), the cationic conjugated polyelectrolyte (CPE) poly[9,9-bis(6-N,N,N-trimethylamonium)hexyl)-fluorene-phenylene)] bromide (HTMA-PFP) and anionic or neutral surfactants (sodium dodecyl sulfonate, SDSu, and n-dodecyl pentaoxyethylene glycol ether, C(12)E(5)) in 4% (v/v) dimethyl sulfoxide (DMSO)-water using UV/visible absorption and fluorescence spectroscopy. Dramatic changes are observed in the spectroscopic behavior of the system depending on the order of addition of the reagents, the surfactant charge, and concentration range. If the neutral C(12)E(5) is added to the HTMA-PFP/dsDNA complex, no significant spectroscopic changes are observed. However, if SDSu is added to the same complex, a dramatic increase of the absorbance and emission intensity is observed for surfactant concentrations above the critical micelle concentration (cmc). In contrast, if dsDNA is added to HTMA-PFP/surfactant systems (with surfactant concentrations above their cmc) no significant changes are observed with SDSu, while a dramatic quenching of polymer emission is observed with C(12)E(5), which can be explained quantitatively in terms of HTMA-PFP/surfactant/DNA complexation and the subsequent polymer aggregation upon charge neutralization. The results are compared with those for the binary systems (HTMA-PFP/DNA and HTMA-PFP/surfactants) and indicate the importance of electrostatic interactions between HTMA-PFP and oppositely charged species in the aggregation processes.
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Affiliation(s)
- María Monteserín
- Departamento de Química, Universidad de Burgos, Burgos 09001, Spain
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24
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Tapia MJ, Montserín M, Valente AJM, Burrows HD, Mallavia R. Binding of polynucleotides to conjugated polyelectrolytes and its applications in sensing. Adv Colloid Interface Sci 2010; 158:94-107. [PMID: 19836007 DOI: 10.1016/j.cis.2009.09.001] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2009] [Revised: 09/10/2009] [Accepted: 09/24/2009] [Indexed: 12/31/2022]
Abstract
We provide a brief overview of the structural characteristics of the main groups of conjugated polyelectrolytes (CPEs) as well as the methods of synthesis and their behaviour in solution. Their tendency to form aggregates in solution, which is one of the key points to be taken into account for them to be used in polynucleotide sensing, is also considered and the various strategies adopted to avoid it will be discussed. These include the synthetic one (with the incorporation of charged and/or bulky substituents), the use of organic co-solvents and the addition of surfactants. The main physical chemical changes (optical, photophysical, electrical conductivity and viscosity) observed upon direct binding between polynucleotide and CPE, the kind of interactions involved and their applicability in sensing are considered as a function of the CPE structural rigidity. Moreover, more complex devices developed in CPE-polynucleotide sensing with the involvement of additional spectroscopic probes to induce Förster resonant energy transfer processes (FRET) or superquenching phenomena are reviewed. Finally, the main CPE applications in biosensing and the potential use of these systems in understanding DNA compaction and possible extension to the construction of supramolecular oligonucleotide structures are summarized.
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Affiliation(s)
- Maria J Tapia
- Departamento de Química, Universidad de Burgos, Plaza Misael Bañuelos, Burgos 09001, Spain.
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25
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Ngo AT, Cosa G. Assembly of zwitterionic phospholipid/conjugated polyelectrolyte complexes: structure and photophysical properties. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2010; 26:6746-6754. [PMID: 20017509 DOI: 10.1021/la904100q] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
We report on the formation of complexes between zwitterionic phospholipid vesicles and an anionic fluorescent conjugated polyelectrolyte and the effect of mono- and divalent cations on the photophysical properties of these complexes. Our goal is to gain an understanding of the interplay of morphology and exciton transport in these complexes, information that is critical to designing efficient lipid/conjugated polymer-based sensors. Our studies further underscore the potential application of lipid/conjugated polymer complexes in light-harvesting devices. Our work focuses on the negatively charged conjugated polyelectrolyte poly[5-methoxy-2-(3-sulfopropoxy)-1,4-phenylenevinylene] (MPS-PPV) and its interaction with the zwitterionic lipid dioleoylphosphatidylcholine (DOPC). We utilize monovalent and divalent cations as a tool to control and explore the interaction of MPS-PPV with lipids. We show that Ca(2+) ions promote the complexation of zwitterionic lipids and MPS-PPV in comparison to Na(+) ions. The addition of increasing amounts of zwitterionic phospholipids in the form of vesicles gradually disrupts MPS-PPV aggregates albeit vesicle structure is preserved in Na(+) buffer. Lipid complexation and the resulting MPS-PPV aggregate disruption produces an intensity enhancement and blue shifting of the MPS-PPV emission peak. In the absence of Ca(2+), the intensity enhancement and blue shift reach a plateau at larger than a 10:1 lipid/MPS-PPV monomer mole ratio. In the presence of Ca(2+), a plateau is reached at equimolar concentrations of MPS-PPV and lipid. Vesicle particle coalescence and agglomerate formation are observed herein. Lipid complexation and concomitant MPS-PPV shielding is shown to diminish the quenching of MPS-PPV emission by water-soluble quencher methyl viologen. FRET experiments conducted with membrane-intercalating acceptor dye DiD further underscore the large lipid/polymer interaction mediated by Ca(2+). We observe efficient light harvesting and MPS-PPV-amplified emission quenching in Ca(2+) buffer and to a lesser extent in Na(+) buffer. Our results highlight how the interplay of a zwitterionic lipid, cations, and buffer, in combination with the conjugated polyelectrolyte MPS-PPV, provides rich diversity in architecture and photophysical properties.
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Affiliation(s)
- An Thien Ngo
- Department of Chemistry, McGill University, 801 Sherbrooke Street West, Montreal, QC, H3A 2K6, Canada
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26
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27
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Pinto SM, Burrows HD, Pereira MM, Fonseca SM, Dias FB, Mallavia R, Tapia MJ. Singlet−Singlet Energy Transfer in Self-Assembled Systems of the Cationic Poly{9,9-bis[6-N,N,N-trimethylammonium)hexyl]fluorene-co-1,4-phenylene} with Oppositely Charged Porphyrins. J Phys Chem B 2009; 113:16093-100. [DOI: 10.1021/jp904959h] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Affiliation(s)
- Sara M. Pinto
- Departamento de Química, Universidade de Coimbra, 3004-535 Coimbra, Portugal, Instituto de Biologia Molecular y Celular, Universidad Miguel Hernández, Elche 03202, Spain, and Departamento de Química, Universidad de Burgos, Plaz Misael Bañuelos, Burgos 09001, Spain
| | - Hugh D. Burrows
- Departamento de Química, Universidade de Coimbra, 3004-535 Coimbra, Portugal, Instituto de Biologia Molecular y Celular, Universidad Miguel Hernández, Elche 03202, Spain, and Departamento de Química, Universidad de Burgos, Plaz Misael Bañuelos, Burgos 09001, Spain
| | - Mariette M. Pereira
- Departamento de Química, Universidade de Coimbra, 3004-535 Coimbra, Portugal, Instituto de Biologia Molecular y Celular, Universidad Miguel Hernández, Elche 03202, Spain, and Departamento de Química, Universidad de Burgos, Plaz Misael Bañuelos, Burgos 09001, Spain
| | - Sofia M. Fonseca
- Departamento de Química, Universidade de Coimbra, 3004-535 Coimbra, Portugal, Instituto de Biologia Molecular y Celular, Universidad Miguel Hernández, Elche 03202, Spain, and Departamento de Química, Universidad de Burgos, Plaz Misael Bañuelos, Burgos 09001, Spain
| | - Fernando B. Dias
- Departamento de Química, Universidade de Coimbra, 3004-535 Coimbra, Portugal, Instituto de Biologia Molecular y Celular, Universidad Miguel Hernández, Elche 03202, Spain, and Departamento de Química, Universidad de Burgos, Plaz Misael Bañuelos, Burgos 09001, Spain
| | - Ricardo Mallavia
- Departamento de Química, Universidade de Coimbra, 3004-535 Coimbra, Portugal, Instituto de Biologia Molecular y Celular, Universidad Miguel Hernández, Elche 03202, Spain, and Departamento de Química, Universidad de Burgos, Plaz Misael Bañuelos, Burgos 09001, Spain
| | - Maria J. Tapia
- Departamento de Química, Universidade de Coimbra, 3004-535 Coimbra, Portugal, Instituto de Biologia Molecular y Celular, Universidad Miguel Hernández, Elche 03202, Spain, and Departamento de Química, Universidad de Burgos, Plaz Misael Bañuelos, Burgos 09001, Spain
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28
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Davies ML, Burrows HD, Cheng S, Morán MC, Miguel MDG, Douglas P. Cationic Fluorene-Based Conjugated Polyelectrolytes Induce Compaction and Bridging in DNA. Biomacromolecules 2009; 10:2987-97. [DOI: 10.1021/bm9004996] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Affiliation(s)
- Matthew L. Davies
- Departamento de Química, Universidade de Coimbra, Rua Larga, 3004-535 Coimbra, Portugal, and Chemistry Group, School of Engineering, and Multidisciplinary Nanotechnology Centre, School of Engineering, Swansea University, Singleton Park, Swansea, SA2 8PP, United Kingdom
| | - Hugh D. Burrows
- Departamento de Química, Universidade de Coimbra, Rua Larga, 3004-535 Coimbra, Portugal, and Chemistry Group, School of Engineering, and Multidisciplinary Nanotechnology Centre, School of Engineering, Swansea University, Singleton Park, Swansea, SA2 8PP, United Kingdom
| | - Shuying Cheng
- Departamento de Química, Universidade de Coimbra, Rua Larga, 3004-535 Coimbra, Portugal, and Chemistry Group, School of Engineering, and Multidisciplinary Nanotechnology Centre, School of Engineering, Swansea University, Singleton Park, Swansea, SA2 8PP, United Kingdom
| | - M. Carmen Morán
- Departamento de Química, Universidade de Coimbra, Rua Larga, 3004-535 Coimbra, Portugal, and Chemistry Group, School of Engineering, and Multidisciplinary Nanotechnology Centre, School of Engineering, Swansea University, Singleton Park, Swansea, SA2 8PP, United Kingdom
| | - Maria da Graça Miguel
- Departamento de Química, Universidade de Coimbra, Rua Larga, 3004-535 Coimbra, Portugal, and Chemistry Group, School of Engineering, and Multidisciplinary Nanotechnology Centre, School of Engineering, Swansea University, Singleton Park, Swansea, SA2 8PP, United Kingdom
| | - Peter Douglas
- Departamento de Química, Universidade de Coimbra, Rua Larga, 3004-535 Coimbra, Portugal, and Chemistry Group, School of Engineering, and Multidisciplinary Nanotechnology Centre, School of Engineering, Swansea University, Singleton Park, Swansea, SA2 8PP, United Kingdom
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