The impact of thermal annealing on the growth of crystalline nanodomains of poly(3-alkylthiophene) (P3AT) in thin films (15−20 nm thick) was investigated as a function of length of alkyl side chain by combined low-dose highresolution transmission electron microscopy (HR-TEM) and grazing incidence X-ray diffraction (GIXD). Statistical analysis of the data yields the characteristic dimensions of the face-on oriented P3AT nanocrystals, i.e., average stem length l c along backbones and lateral dimension perpendicular to the stems l a along side chains. The following trends were identified: (i) in as-spin-coated films, the proportion of face-on oriented nanocrystals increases with the number of carbon atoms in the side chain, (ii) annealing favors the lateral in-plane growth of the nanocrystals along the side chain direction (a P3AT axis), (iii) for a given P3AT, the proportion of face-on oriented domains increases with annealing temperature, (iv) lateral growth along the a P3AT axis is most efficient for the longer octyl side chains, and (v) thermal annealing induces only modest lamellar thickening which is limited by the poor slide diffusion of π-stacked P3AT chains as opposed to lateral growth favored by weak van der Waals interactions between layers of n-alkyl side chains. The increase in the population of face-on oriented crystallites, observed when the length of the side chain increases, coincides with a corresponding decrease in the field effect mobility in annealed P3AT thin films.
The recent COVID-19 pandemic is uncontrollable since the SARS-CoV-2 virus has a contagious transmission and causes fatal illness. Thus, it is vital to avoid this spread using high-performance antiviral nanomaterials to eradicate viral infections.
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.
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