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

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

Research output: Contribution to journalArticlepeer-review

16 Citations (Scopus)
36 Downloads (Pure)

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
Number of pages9
JournalCrystal Growth & Design
Volume16
Issue number9
DOIs
Publication statusPublished - 18 Jul 2016

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