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Understanding the Structural Evolution of Single Conjugated Polymer Chain Conformers

Single molecule photoluminescence (PL) spectroscopy of conjugated polymers has shed new light on the complex structure–function relationships of these materials. Although extensive work has been carried out using polarization and excitation intensity modulated experiments to elucidate conformation-d...

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Autores principales: Wise, Adam J., Grey, John K.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: MDPI 2016
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6432208/
https://www.ncbi.nlm.nih.gov/pubmed/30974664
http://dx.doi.org/10.3390/polym8110388
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author Wise, Adam J.
Grey, John K.
author_facet Wise, Adam J.
Grey, John K.
author_sort Wise, Adam J.
collection PubMed
description Single molecule photoluminescence (PL) spectroscopy of conjugated polymers has shed new light on the complex structure–function relationships of these materials. Although extensive work has been carried out using polarization and excitation intensity modulated experiments to elucidate conformation-dependent photophysics, surprisingly little attention has been given to information contained in the PL spectral line shapes. We investigate single molecule PL spectra of the prototypical conjugated polymer poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) which exists in at least two emissive conformers and can only be observed at dilute levels. Using a model based on the well-known “Missing Mode Effect” (MIME), we show that vibronic progression intervals for MEH-PPV conformers can be explained by relative contributions from particular skeletal vibrational modes. Here, observed progression intervals do not match any ground state Raman active vibrational frequency and instead represent a coalescence of multiple modes in the frequency domain. For example, the higher energy emitting “blue” MEH-PPV form exhibits PL maxima at ~18,200 cm(−1) with characteristic MIME progression intervals of ~1200–1350 cm(−1), whereas the lower energy emitting “red” form peaks at ~17,100 cm(−1) with intervals in the range of ~1350–1450 cm(−1). The main differences in blue and red MEH-PPV chromophores lie in the intra-chain order, or, planarity of monomers within a chromophore segment. We demonstrate that the Raman-active out-of-plane C–H wag of the MEH-PPV vinylene group (~966 cm(−1)) has the greatest influence in determining the observed vibronic progression MIME interval. Namely, larger displacements (intensities)—indicating lower intra-chain order—lower the effective MIME interval. This simple model provides useful insights into the conformational characteristics of the heterogeneous chromophore landscape without requiring costly and time-consuming low temperature or single molecule Raman capabilities.
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spelling pubmed-64322082019-04-02 Understanding the Structural Evolution of Single Conjugated Polymer Chain Conformers Wise, Adam J. Grey, John K. Polymers (Basel) Article Single molecule photoluminescence (PL) spectroscopy of conjugated polymers has shed new light on the complex structure–function relationships of these materials. Although extensive work has been carried out using polarization and excitation intensity modulated experiments to elucidate conformation-dependent photophysics, surprisingly little attention has been given to information contained in the PL spectral line shapes. We investigate single molecule PL spectra of the prototypical conjugated polymer poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) which exists in at least two emissive conformers and can only be observed at dilute levels. Using a model based on the well-known “Missing Mode Effect” (MIME), we show that vibronic progression intervals for MEH-PPV conformers can be explained by relative contributions from particular skeletal vibrational modes. Here, observed progression intervals do not match any ground state Raman active vibrational frequency and instead represent a coalescence of multiple modes in the frequency domain. For example, the higher energy emitting “blue” MEH-PPV form exhibits PL maxima at ~18,200 cm(−1) with characteristic MIME progression intervals of ~1200–1350 cm(−1), whereas the lower energy emitting “red” form peaks at ~17,100 cm(−1) with intervals in the range of ~1350–1450 cm(−1). The main differences in blue and red MEH-PPV chromophores lie in the intra-chain order, or, planarity of monomers within a chromophore segment. We demonstrate that the Raman-active out-of-plane C–H wag of the MEH-PPV vinylene group (~966 cm(−1)) has the greatest influence in determining the observed vibronic progression MIME interval. Namely, larger displacements (intensities)—indicating lower intra-chain order—lower the effective MIME interval. This simple model provides useful insights into the conformational characteristics of the heterogeneous chromophore landscape without requiring costly and time-consuming low temperature or single molecule Raman capabilities. MDPI 2016-11-03 /pmc/articles/PMC6432208/ /pubmed/30974664 http://dx.doi.org/10.3390/polym8110388 Text en © 2016 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC-BY) license (http://creativecommons.org/licenses/by/4.0/).
spellingShingle Article
Wise, Adam J.
Grey, John K.
Understanding the Structural Evolution of Single Conjugated Polymer Chain Conformers
title Understanding the Structural Evolution of Single Conjugated Polymer Chain Conformers
title_full Understanding the Structural Evolution of Single Conjugated Polymer Chain Conformers
title_fullStr Understanding the Structural Evolution of Single Conjugated Polymer Chain Conformers
title_full_unstemmed Understanding the Structural Evolution of Single Conjugated Polymer Chain Conformers
title_short Understanding the Structural Evolution of Single Conjugated Polymer Chain Conformers
title_sort understanding the structural evolution of single conjugated polymer chain conformers
topic Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6432208/
https://www.ncbi.nlm.nih.gov/pubmed/30974664
http://dx.doi.org/10.3390/polym8110388
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