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Intermolecular Interactions and Energetics in the Crystalline π–π Stacks and Associated Model Dimer Systems of Asymmetric Halogenated Diketopyrrolopyrroles

DOI: 10.1021/acs.cgd.5b01656 DOI Help

Authors: Jesus Calvo-castro (University of the West of Scotland) , Monika Warzecha (University of Strathclyde) , Iain D. H. Oswald (University of Strathclyde) , Alan R. Kennedy (University of Strathclyde) , Graeme Morris (University of the West of Scotland) , Andrew J. Mclean (University of the West of Scotland) , Callum J. Mchugh (University of the West of Scotland)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Crystal Growth & Design , VOL 16 , PAGES 1531 - 1542

State: Published (Approved)
Published: March 2016

Abstract: Four novel structurally analogous asymmetric, halogenated N-benzyl substituted diketopyrrolopyrroles (DPP) have been synthesized, and their crystal structures obtained. All four crystal structures exhibit π–π stacks with very small displacements along their short molecular axes, which based upon our previous studies involving symmetrical DPPs is a characteristic of N-benzyl substitution. Intermolecular interaction energies were computed for extracted crystal π–π dimer pairs by means of M06-2X density functional at the 6-311G(d) level to investigate the most energetically favored position of the halogen atoms in FBDPP and ClBDPP structures. In addition, effective stabilization energies arising from both benzyl and halogen substitution in these derivatives and in BrBDPP and IBDPP π–π dimer pairs were determined in order to probe the impact of these groups on the resulting dimer stability. Effects of the intermonomer displacements along the long molecular axis, which have been shown by us previously to significantly influence wavefunction overlap and effective electronic coupling, were investigated in detail using aligned and anti-aligned model systems of ClDPP and BrDPP. The predictions of these model systems are remarkably consistent with the observed displacements in their crystal derived π–π dimer pair equivalents, offering insight into the effective role of intermolecular contacts in crystal structures involving this molecular motif, particularly with a view toward crystal engineering in these systems. As a result, we believe that this study should be of significant interest to the growing DPP based materials community and in general to those investigating the detailed manner by which substituents can be employed in the supramolecular design of crystalline molecular architectures.

Subject Areas: Chemistry

Instruments: I19-Small Molecule Single Crystal Diffraction