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Switching between H- and J-type electronic coupling in single conjugated polymer aggregates.

ABSTRACT: The aggregation of conjugated polymers and electronic coupling of chromophores play a central role in the fundamental understanding of light and charge generation processes. Here we report that the predominant coupling in isolated aggregates of conjugated polymers can be switched reversibly between H-type and J-type coupling by partially swelling and drying the aggregates. Aggregation is identified by shifts in photoluminescence energy, changes in vibronic peak ratio, and photoluminescence lifetime. This experiment unravels the internal electronic structure of the aggregate and highlights the importance of the drying process in the final spectroscopic properties. The electronic coupling after drying is tuned between H-type and J-type by changing the side chains of the conjugated polymer, but can also be entirely suppressed. The types of electronic coupling correlate with chain morphology, which is quantified by excitation polarization spectroscopy and the efficiency of interchromophoric energy transfer that is revealed by the degree of single-photon emission.

SUBMITTER: Eder T

PROVIDER: S-EPMC5696370 | biostudies-literature | 2017 Nov

REPOSITORIES: biostudies-literature

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Switching between H- and J-type electronic coupling in single conjugated polymer aggregates.

Eder Theresa T Stangl Thomas T Gmelch Max M Remmerssen Klaas K Laux Dirk D Höger Sigurd S Lupton John M JM Vogelsang Jan J

Nature communications 20171121 1

The aggregation of conjugated polymers and electronic coupling of chromophores play a central role in the fundamental understanding of light and charge generation processes. Here we report that the predominant coupling in isolated aggregates of conjugated polymers can be switched reversibly between H-type and J-type coupling by partially swelling and drying the aggregates. Aggregation is identified by shifts in photoluminescence energy, changes in vibronic peak ratio, and photoluminescence lifet ...[more]

PMID: 29158508

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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

Switching between H- and J-type electronic coupling in single conjugated polymer aggregates.

Publications

Switching between H- and J-type electronic coupling in single conjugated polymer aggregates.

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