Control of conformational and interpolymer effects in conjugated polymers

J, Kim; Swager, Timothy M.

doi:10.1038/35082528

Cited by 483 publications

(487 citation statements)

References 20 publications

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“…The disappearance of the peak from the terminal phenyl acetylene indicates nearly complete conversion of the monomers in the SAM to the corresponding linked monolayer. A variety of conjugated polymers have been previously synthesized that resemble these linked monolayers (20,21,26,27). The spectroscopic changes observed in the monolayersupported systems are similar to those seen in the literature examples.…”

Section: Resultssupporting

confidence: 62%

Synthesis of linked carbon monolayers: Films, balloons, tubes, and pleated sheets

Schultz

Zhang

Unarunotai

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

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Because of their potential for use in advanced electronic, nanomechanical, and other applications, large two-dimensional, carbon-rich networks have become an important target to the scientific community. Current methods for the synthesis of these materials have many limitations including lack of molecular-level control and poor diversity. Here, we present a method for the synthesis of two-dimensional carbon nanomaterials synthesized by Mo-and Cu-catalyzed cross-linking of alkyne-containing selfassembled monolayers on SiO 2 and Si3N4. When deposited and cross-linked on flat surfaces, spheres, cylinders, or textured substrates, monolayers take the form of these templates and retain their structure on template removal. These nanomaterials can also be transferred from surface to surface and suspended over cavities without tearing. This approach to the synthesis of monolayer carbon networks greatly expands the chemistry, morphology, and size of carbon films accessible for analysis and device applications.networks ͉ nanomaterials ͉ self-assembled I n contrast to carbon nanotubes, fullerenes and various derivatives (1-3), the synthesis of large 2D sheets such as graphene (4), graphyne, and graphdiyne (5, 6) extending over micrometers in lateral dimensions is either in its infancy or has significant limitations. In fact, the synthesis of 2D carbon networks has been recognized as an outstanding challenge in materials chemistry (7).Graphene, the simplest of the 2D conjugated carbon nanomaterials, is produced by micromechanical cleavage of bulk graphite (HOPG) or by thermal decomposition of silicon carbide (8, 9). However, these approaches lack the molecular-level control necessary to define the chemical makeup of these systems. Scholl coupling reactions on oligophenylene precursors (10) produce small (Ͻ15 nm) 2D graphene fragments with improved molecular diversity, and radiation induced modifications of self-assembled (11, 12) or Langmuir-Blodgett (13) monolayers create larger sheets, but with reduced control of the chemistry. Polyelectrolytes (14) represent a different class of chemistry that can form 2D (15) and 3D (16) nanomaterials. These films are formed through deposition of separately synthesized polymers, often in layer-by-layer assemblies, in the form of relatively thick (typically Ͼ5 nm) films governed by electrostatic interactions. These limitations, together with those associated with the planar, radiation-cross-linked monolayers, motivate the need for alternative approaches to these classes of materials.A potential solution to the formation of large 2D conjugated carbon nanomaterials would employ a two-step procedure involving the formation of self-assembled monolayers (SAMs) with highly functionalized monomers followed by chemical crosslinkage of the SAMs to form linked monolayers. Fig. 1 shows the overall process beginning with the formation of SAMs of suitably designed carbon precursors on solid supports, followed by chemical cross-linking to yield covalently bonded networks with monolayer thicknesses. Not...

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Section: Resultssupporting

confidence: 62%

Synthesis of linked carbon monolayers: Films, balloons, tubes, and pleated sheets

Schultz

Zhang

Unarunotai

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

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“…57 The photophysical spectra and properties of polymer 9 are summarized in Figure 4. The broad excimer emission (510 nm) in the fluorescence Energy transfer efficiencies between polymer 9 and fluorophores 2-6b measured by the decrease in polymer emission (E exp ) and the increase in fluorophore emission (I AD /I A ) To estimate HOMO and LUMO levels, the oxidation and reduction potential of fluorophores were obtained by cyclic voltammetry, and the energy levels obtained from the potential differences 93-94 (electrochemical band gap) were compared to the onset wavelengths of the absorption spectra (optical band gap) ( Table 5 d The CVs of compounds 7b and 7c did not provide well-defined oxidation and reduction peaks.…”

Section: Comparison To a Simple Ppementioning

confidence: 99%

Photoluminescent energy transfer from poly(phenyleneethynylene)s to near‐infrared emitting fluorophores

Levine

Song

Andrew

et al. 2010

J. Polym. Sci. A Polym. Chem.

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Photoluminescent energy transfer was investigated in conjugated polymer-fluorophore blended thin films. A pentiptycene-containing poly(phenyleneethynylene) was used as the energy donor, and 13 fluorophores were used as energy acceptors. The efficiency of energy transfer was measured by monitoring both the quenching of the polymer emission IntroductionThe highly efficient energy transfer 1 and exciton migration processes 2 in conjugated polymers can be exploited in various electronic applications 3-11 and in amplifying sensor responses. [12][13][14][15][16][17][18][19] Highly sensitive, amplified quenching of polymer emission has been accomplished with various quenchers in solution as well as in the solid state. [20][21][22][23][24][25] Applications of this amplified quenching include the detection of chemical and biological analytes, 26-38 and explosives. 39 In contrast to turn-off sensors based on amplified polymer quenching, turn-on sensors have the advantage of potentially being even more sensitive and selective, 40-41 especially if the new signal can be generated on a completely dark background. Some examples of turn-on sensors have been developed previously. [42][43][44][45] In many of these sensors, the emission spectrum of the donor overlaps with the emission spectrum of the acceptor. This overlap leads to decreased sensitivity in turn-on sensory applications, as even in the absence of the acceptor there is background donor emission in the same spectral region, and hence not the desired completely dark background.Recent results from our group have demonstrated superior energy transfer with reduced spectral overlap between the absorption spectra of the streptavidin-functionalized fluorophore acceptors and the emission spectrum of the biotin-functionalized Additionally, turn-on sensors that display a new fluorescence emission in the nearinfrared (NIR) region (650-900 nm) are highly desirable for biological applications. [47][48] Biological chromophores exhibit low absorption and auto-fluorescence in this spectral region, which allows photons to penetrate biological tissue. 49 Some applications of NIR fluorophores in biological imaging have been reported; 50-55 however, the use of conjugated polymers as energy donors in combination with NIR energy acceptors allows for highly amplified fluorescence emission in a spectral region that is free of interfering signals (neither the polymer donor nor biological analytes fluoresce in this region).We report herein a thorough investigation of the energy transfer between a conjugated PPE and 13 commercially available and readily-synthesized fluorophores. These compounds have absorption maxima ranging from 537 nm to 686 nm, with many of the compounds absorbing and fluorescing in the NIR region. We show highly efficient energy transfer from the PPE to the fluorophores, with nearly 100-fold fluorescence amplification in the NIR region from exciting the PPE compared to exciting a squaraine chromophore directly. Experimental

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“…A wide range of spectroscopic properties, previously associated with interchromophoric interactions, are observed in the isolated chromophore. 9,20,21 Remarkably, the fluorescence linewidth correlates with polarization anisotropy, which provides a direct measure of chromophore conformation. In agreement with recent investigations of the twisting of single biphenyl units, 22 we find that even the shortest oligomers (7mers) can support a curvature of up to ∼80°without loss of conjugation.…”

mentioning

confidence: 99%

“…We previously linked the broadened spectral features to self-aggregation of multiple chromophores on a single chain, 9,26 following wellestablished assignments from ensemble spectroscopy. 20, 21 The fact that equal spectral signatures are observed in short oligomers and long polymer chains, however, illustrates that spectral broadening in the single chain emission cannot be due to interchromophoric contacts.…”

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confidence: 99%

How Chromophore Shape Determines the Spectroscopy of Phenylene−Vinylenes: Origin of Spectral Broadening in the Absence of Aggregation

et al. 2008

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Single oligo(phenylene-vinylene) molecules constitute model systems of chromophores in disordered conjugated polymers and can elucidate how the actual conformation of an individual chromophore, rather than that of an overall polymer chain, controls its photophysics. Single oligomers and polymer chains display the same range of spectral properties. Even heptamers support π-electron conjugation across ∼80°curvature, as revealed by the polarization anisotropy in excitation and supported by quantum chemical calculations. As the chain becomes more deformed, the spectral linewidth at low temperatures, often interpreted as a sign of aggregation, increases up to 30-fold due to a reduction in photophysical stability of the molecule and an increase in random spectral fluctuations. The conclusions aid the interpretation of results from single-chain Stark spectroscopy in which large static dipoles were only observed in the case of narrow transition lines. These narrow transitions originate from extended chromophores in which the dipoles induced by backbone substituents do not cancel out. Chromophores in conjugated polymers are often thought of as individual linear transition dipoles, the sum of which make up the polymer's optical properties. Our results demonstrate that, at least for phenylene-vinylenes, it is the actual shape of the individual chromophore rather than the overall chromophoric arrangement and form of the polymer chain that dominates the spectroscopic properties.Molecular-level engineering in plastic electronics requires a precise understanding of how a particular physical or chemical structure impacts on the physical properties of the material. Disorder effects on the ensemble level can often mask the subtle interplay between function and structure. Large macromolecules such as conjugated polymers are particularly prone to energetic disorder, which gives rise to substantial spectral broadening and is generally attributed to a "particle in a box"-like picture of varying chromophore lengths. 1 Disorder effects have commonly been investigated in matrix isolated materials, such as polyenes, where subtle interplays between molecular shape and electronic structure have been identified. 2-5 However, matrix isolation on its own is not sufficient to overcome disorder but merely helps to screen intermolecular effects. The intrinsic molecular properties themselves are accessible with single-molecule spectroscopy. Although this technique helps to overcome the ensemble limitations, a single polymer chain can still contain many chromophores. [6][7][8][9][10][11][12] Energy transfer between these chromophores can mask the true photophysics of the individual spectroscopic unit. Although polarization-resolved spectroscopy has yielded detailed insight into the conformation of the polymer chain, 7,8,11,[13][14][15] very little is known about the shape of the indiVidual chromophore. Because a physical bend can potentially interrupt the π-electron conjugation, the chromophore is generally thought to be linearly extended in space...

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Control of conformational and interpolymer effects in conjugated polymers

Cited by 483 publications

References 20 publications

Synthesis of linked carbon monolayers: Films, balloons, tubes, and pleated sheets

Synthesis of linked carbon monolayers: Films, balloons, tubes, and pleated sheets

Photoluminescent energy transfer from poly(phenyleneethynylene)s to near‐infrared emitting fluorophores

How Chromophore Shape Determines the Spectroscopy of Phenylene−Vinylenes: Origin of Spectral Broadening in the Absence of Aggregation

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