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Issue 31, 2017
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The correspondence between the conformational and chromophoric properties of amorphous conjugated polymers in mesoscale condensed systems

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Abstract

For π-conjugated polymers, the notion of spectroscopic units or “chromophores” provides illuminating insights into the experimentally observed absorption/emission spectra and the mechanisms of energy/charge transfer. To date, however, no statistical analysis has revealed a direct correspondence between chromophoric and conformational properties—with the latter being fundamental to polymer semiconductors. Herein, we propose a “persistence length” calculation to re-evaluate chain conformation over a full conjugation length. The mesoscale condensed systems of MEH-PPV and MEH-PPV/C60 hybrid (system size ∼10 × 10 × 10 nm3) are utilized as two prototypical model systems, along with a full range of segmental lengths (2–20-mer) and five lowest singlet excited states to hint at the generality of the features presented. We demonstrate, for the first time, that two properly re-defined conformational factors that characterize chain folding and planarity, respectively, capture excellently the population distribution of chromophores in both systems investigated. In contrast, the conventional strategy of utilizing two adjacent monomer units to characterize (local) chain conformation results in only an inconspicuous correlation between the two, as previously reported. It is further shown that chain folding—and not chain planarity—is more relevant in capturing the associated oscillator strength for the first excited state, where the transient dipole moments are known to align with the chain conformation, although the corresponding excitation energy and exciton size seem relatively unaffected. The observed effects of C60 on the MEH-PPV adsorption spectra also agree with recent experimental trends. Overall, the present findings are expected to aid future multiscale computer simulations and spectroscopy-data interpretations for polymer semiconductors and their hybrid systems.

Graphical abstract: The correspondence between the conformational and chromophoric properties of amorphous conjugated polymers in mesoscale condensed systems

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Publication details

The article was received on 22 May 2017, accepted on 13 Jul 2017 and first published on 13 Jul 2017


Article type: Paper
DOI: 10.1039/C7CP03415F
Citation: Phys. Chem. Chem. Phys., 2017,19, 20818-20828
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    The correspondence between the conformational and chromophoric properties of amorphous conjugated polymers in mesoscale condensed systems

    C. I. Wang, C. H. Hsu and C. C. Hua, Phys. Chem. Chem. Phys., 2017, 19, 20818
    DOI: 10.1039/C7CP03415F

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