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

Abstract

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

Topics

• density
• impedance spectroscopy
• single crystal
• grain
• thin film
• defect
• two-dimensional