Polymorphism in Bulk and Thin Films: The Curious Case of Dithiophene-DPP(Boc)-Dithiophene

Abstract

Polymorphism is an interesting phenomenon critical to our understanding of structure−property relationships in solid-state functional materials. We report the synthesis and structural characterization of two polymorphic forms of a DPP-Boc derivative, DPP4T-α and DPP4T-β, as well as the study of their optical properties. Thin film studies have been carried out to identify the specific polymorphic form that exists in contact with the substrate and also to obtain a better understanding of the interface morphology with respect to crystal packing. The two polymorphs, DPP4T-α and DPP4T-β, have been structurally characterized using single crystal/powder X-ray diffraction data with a detailed analysis of Hirshfeld surfaces and fingerprint plots facilitating a comparison of the type and nature of intermolecular interactions in the supramolecular architectures. DPP4T-α crystallizing in a space group P2 1 /c with Z′ = 0.5 interlinked via C−H•••O/π and π•••π interactions forms 2D herringbone sheets. In the polymorph DPP4T-β with space group P1 and Z′ = 1, the crystal packing is stabilized by CH•••π and π•••π interactions forming a columnar network. From considerations of density and from lattice energy calculations, it can be concluded that the αform is more stable in bulk. In thin films the β-form was found to be more stable. This work gives a unique example where the polymorphism could be identified and separated both in the bulk and in thin films. This study on the structural effects of polymorphism is useful for further development of DPP-based materials and also for targeted design of other functional materials.

Computational study of structure, electronic, and microscopic charge transport properties of small conjugated diketopyrrolopyrrole‐thiophene molecules

“…Also it should be noted that the packing densities 1.394 and 1.376 g cm −3 of chosen structures P 2 1 of conformer 1 and P 2 1 2 1 2 1 of conformer 2 , respectively, correlate with experimentally observed ones for crystals of related molecules …”

“…Numerous papers have been published by researchers worldwide on synthesis and experimental study of small oligothiophene‐flanked DPP molecules . For instance, for a series of DPP molecules symmetrically disubstituted with oligothiophenes, it was shown that electrochemical properties were affected to a significant extent by the length of oligothiophene units and the position of the substituent in it, but were independent of the type of alkyl N‐substituent .…”

Substrate‐Induced and Thin‐Film Phases: Polymorphism of Organic Materials on Surfaces

“…The stabilization of the β ‐form in thin films is facilitated by solvent vapor annealing of films containing the α ‐phase. It is also possible for both polymorphic forms to be isolated in the bulk by varying the conditions during recrystallization …”

Correlating Charge Transport with Structure in Deconstructed Diketopyrrolopyrrole Oligomers: A Case Study of a Monomer in Field-Effect Transistors

“…[16][17] Further, polymorphism plays a large role in governing crystal structure and consequently charge transport. [18][19][20][21] By using compositionally identical but structurally different guest-host systems based on TES-ADTs, it was shown that FET carrier mobilities are greatly reduced by adding the syn isomer to anti TES-ADT. 22 By considering non-covalent interactions, quantum chemical investigations from isomers of functionalized oligoacenes highlight the mechanism of enhanced charge transport properties in "brickwork" configuration compared to "slipped-stack" structures.…”