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Anisotropic Conjugated Polymer Chain Conformation Tailors the Energy Migration in Nanofibers.

ABSTRACT: Conjugated polymers are complex multichromophore systems, with emission properties strongly dependent on the electronic energy transfer through active subunits. Although the packing of the conjugated chains in the solid state is known to be a key factor to tailor the electronic energy transfer and the resulting optical properties, most of the current solution-based processing methods do not allow for effectively controlling the molecular order, thus making the full unveiling of energy transfer mechanisms very complex. Here we report on conjugated polymer fibers with tailored internal molecular order, leading to a significant enhancement of the emission quantum yield. Steady state and femtosecond time-resolved polarized spectroscopies evidence that excitation is directed toward those chromophores oriented along the fiber axis, on a typical time scale of picoseconds. These aligned and more extended chromophores, resulting from the high stretching rate and electric field applied during the fiber spinning process, lead to improved emission properties. Conjugated polymer fibers are relevant to develop optoelectronic plastic devices with enhanced and anisotropic properties.

SUBMITTER: Camposeo A

PROVIDER: S-EPMC5133673 | biostudies-literature | 2016 Nov

REPOSITORIES: biostudies-literature

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Anisotropic Conjugated Polymer Chain Conformation Tailors the Energy Migration in Nanofibers.

Camposeo Andrea A Pensack Ryan D RD Moffa Maria M Fasano Vito V Altamura Davide D Giannini Cinzia C Pisignano Dario D Scholes Gregory D GD

Journal of the American Chemical Society 20161117 47

Conjugated polymers are complex multichromophore systems, with emission properties strongly dependent on the electronic energy transfer through active subunits. Although the packing of the conjugated chains in the solid state is known to be a key factor to tailor the electronic energy transfer and the resulting optical properties, most of the current solution-based processing methods do not allow for effectively controlling the molecular order, thus making the full unveiling of energy transfer m ...[more]

PMID: 27933935

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Project 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.

Dataset Information

Anisotropic Conjugated Polymer Chain Conformation Tailors the Energy Migration in Nanofibers.

Publications

Anisotropic Conjugated Polymer Chain Conformation Tailors the Energy Migration in Nanofibers.

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