Fluorine Directed Two-Dimensional Cruciform π−π Stacking in Diketopyrrolopyrroles

Jesus Calvo-Castro, Graeme Morris, Alan R. Kennedy, Callum McHugh

Research output: Contribution to journalArticle

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Abstract

Enhanced bulk dimensionality in organic materials employed in optoelectronic devices is desirable and can overcome fabrication issues related to structural defects and grain boundaries. Herein, we report a novel fluorinated diketopyrrolopyrrole single crystal structure, which displays a unique, mutually orthogonal, 2-dimensional cruciform π–π stacking arrangement. The crystal structure is characterized by an unusually large number of nearest neighbor dimer pairs which contribute to a greater thermal integrity than structurally analogous equivalents. Binding energies and charge transfer integrals were computed for all of the crystal extracted dimer pairs by means of the M06-2X density functional at the 6-311G(d) level. Although weak, a number of intermolecular interactions involving organic fluorine (C–F---H, πF---π, and C–F---πF) were identified to influence the supramolecular assembly of these dimer pairs. Charge transfer integrals for the two π–π stacking crystal dimers were determined using the energy splitting in dimer method. Ambipolar charge transport favoring electron transfer approaching that of rubrene is predicted in both of these π–π stacks, with a greater magnitude of coupling observed from those dimers perpetuating along the crystallographic a-axis. Charge transport behavior in the single crystal is greatly influenced by selective fluorination of the N-benzyl substituents and is consistent with the crystal extracted π–π stacking dimer geometries and their overall influence on wave function overlap. The reported structure is an interesting electron transport material that could be exploited, particularly in thin film based optoelectronic devices, where high bulk dimensionality is required.

Original languageEnglish
Pages (from-to)5385−5393
JournalCrystal Growth & Design
Volume16
Issue number9
Early online date18 Jul 2016
DOIs
Publication statusPublished - 7 Sep 2016

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Fluorine
Dimers
fluorine
dimers
Charge transfer
optoelectronic devices
Optoelectronic devices
Crystals
Crystal structure
charge transfer
Single crystals
crystals
Fluorination
crystal structure
fluorination
single crystals
Wave functions
organic materials
Binding energy
Energy transfer

Cite this

Calvo-Castro, Jesus ; Morris, Graeme ; Kennedy, Alan R. ; McHugh, Callum. / Fluorine Directed Two-Dimensional Cruciform π−π Stacking in Diketopyrrolopyrroles. In: Crystal Growth & Design. 2016 ; Vol. 16, No. 9. pp. 5385−5393.
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Fluorine Directed Two-Dimensional Cruciform π−π Stacking in Diketopyrrolopyrroles. / Calvo-Castro, Jesus; Morris, Graeme; Kennedy, Alan R. ; McHugh, Callum.

In: Crystal Growth & Design, Vol. 16, No. 9, 07.09.2016, p. 5385−5393.

Research output: Contribution to journalArticle

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T1 - Fluorine Directed Two-Dimensional Cruciform π−π Stacking in Diketopyrrolopyrroles

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N2 - Enhanced bulk dimensionality in organic materials employed in optoelectronic devices is desirable and can overcome fabrication issues related to structural defects and grain boundaries. Herein, we report a novel fluorinated diketopyrrolopyrrole single crystal structure, which displays a unique, mutually orthogonal, 2-dimensional cruciform π–π stacking arrangement. The crystal structure is characterized by an unusually large number of nearest neighbor dimer pairs which contribute to a greater thermal integrity than structurally analogous equivalents. Binding energies and charge transfer integrals were computed for all of the crystal extracted dimer pairs by means of the M06-2X density functional at the 6-311G(d) level. Although weak, a number of intermolecular interactions involving organic fluorine (C–F---H, πF---π, and C–F---πF) were identified to influence the supramolecular assembly of these dimer pairs. Charge transfer integrals for the two π–π stacking crystal dimers were determined using the energy splitting in dimer method. Ambipolar charge transport favoring electron transfer approaching that of rubrene is predicted in both of these π–π stacks, with a greater magnitude of coupling observed from those dimers perpetuating along the crystallographic a-axis. Charge transport behavior in the single crystal is greatly influenced by selective fluorination of the N-benzyl substituents and is consistent with the crystal extracted π–π stacking dimer geometries and their overall influence on wave function overlap. The reported structure is an interesting electron transport material that could be exploited, particularly in thin film based optoelectronic devices, where high bulk dimensionality is required.

AB - Enhanced bulk dimensionality in organic materials employed in optoelectronic devices is desirable and can overcome fabrication issues related to structural defects and grain boundaries. Herein, we report a novel fluorinated diketopyrrolopyrrole single crystal structure, which displays a unique, mutually orthogonal, 2-dimensional cruciform π–π stacking arrangement. The crystal structure is characterized by an unusually large number of nearest neighbor dimer pairs which contribute to a greater thermal integrity than structurally analogous equivalents. Binding energies and charge transfer integrals were computed for all of the crystal extracted dimer pairs by means of the M06-2X density functional at the 6-311G(d) level. Although weak, a number of intermolecular interactions involving organic fluorine (C–F---H, πF---π, and C–F---πF) were identified to influence the supramolecular assembly of these dimer pairs. Charge transfer integrals for the two π–π stacking crystal dimers were determined using the energy splitting in dimer method. Ambipolar charge transport favoring electron transfer approaching that of rubrene is predicted in both of these π–π stacks, with a greater magnitude of coupling observed from those dimers perpetuating along the crystallographic a-axis. Charge transport behavior in the single crystal is greatly influenced by selective fluorination of the N-benzyl substituents and is consistent with the crystal extracted π–π stacking dimer geometries and their overall influence on wave function overlap. The reported structure is an interesting electron transport material that could be exploited, particularly in thin film based optoelectronic devices, where high bulk dimensionality is required.

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