Polymorphism of organic semiconductor

Organic semiconductors exhibit high versatility and large number of advantages in the electronic fields because of their solution-processability and low cost of production. However, possible polymorphism, due to the fact that organic molecules can adopt different crystal packings, may induce variation in electronic, mechanical, or optical properties at the solid state. Indeed, even small changes in the packing of organic semiconductors affect their electronic performances by orders of magnitude.

Although polymorph screening is not widely popular for organic electronics, while it is a well-established standard technique for pharmaceutical molecules, an understanding of crystal packing provides thorough knowledge of the structure−property relationships and mechanical behaviour of organic semiconductors.

Elettra's contribution

Polymorphic and structural studies of a novel organic semiconductor have been carried out and revealed the presence of three crystal forms, as the thermodynamically stable Form I structure dominates at room temperature, while Form II and Form III are metastable.
Furthermore, the collaborators taking part in the study tested the mechanical properties of Form I crystals, which exhibit anisotropic plastic flexibility. This mechanical behavior is an additional benefit of the semiconductor because offer a great advantage for better and flexible device, especially considering that most organic molecules exhibit brittle or elastic behavior. The study revealed that polymorphism can serve as a great tool to enhance charge carrier mobilities of organic semiconductor without having to modify the compound chemically.

Facility: XRD2 Beamline.

Bibliography: P. Pandey et al., “Discovering Crystal Forms of the Novel Molecular Semiconductor”, Cryst. Growth Des. 2022, 22, 1680−1690. DOI: 10.1021/acs.cgd.1c01203

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