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A computational exploration of the crystal energy and charge-carrier mobility landscapes of the chiral [6]helicene molecule

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Abstract

The potential of a given π-conjugated organic molecule in an organic semiconductor device is highly dependent on molecular packing, as it strongly influences the charge-carrier mobility of the material. Such solid-state packing is sensitive to subtle differences in their intermolecular interactions and is challenging to predict. Chirality of the organic molecule adds an additional element of complexity to intuitive packing prediction. Here we use crystal structure prediction to explore the lattice-energy landscape of a potential chiral organic semiconductor, [6]helicene. We reproduce the experimentally observed enantiopure crystal structure and explain the absence of an experimentally observed racemate structure. By exploring how the hole and electron-mobility varies across the energy–structure–function landscape for [6]helicene, we find that an energetically favourable and frequently occurring packing motif is particularly promising for electron-mobility, with a highest calculated mobility of 2.9 cm2 V−1 s−1 (assuming a reorganization energy of 0.46 eV). We also calculate relatively high hole-mobility in some structures, with a highest calculated mobility of 2.0 cm2 V−1 s−1 found for chains of helicenes packed in a herringbone fashion. Neither the energetically favourable nor high charge-carrier mobility packing motifs are intuitively obvious, and this demonstrates the utility of our approach to computationally explore the energy–structure–function landscape for organic semiconductors. Our work demonstrates a route for the use of computational simulations to aid in the design of new molecules for organic electronics, through the a priori prediction of their likely solid-state form and properties.

Graphical abstract: A computational exploration of the crystal energy and charge-carrier mobility landscapes of the chiral [6]helicene molecule

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Publication details

The article was received on 28 Nov 2017, accepted on 27 Dec 2017 and first published on 05 Jan 2018


Article type: Paper
DOI: 10.1039/C7NR08890F
Citation: Nanoscale, 2018, Advance Article
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    A computational exploration of the crystal energy and charge-carrier mobility landscapes of the chiral [6]helicene molecule

    B. Rice, L. M. LeBlanc, A. Otero-de-la-Roza, M. J. Fuchter, E. R. Johnson, J. Nelson and K. E. Jelfs, Nanoscale, 2018, Advance Article , DOI: 10.1039/C7NR08890F

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