Covalent Topochemical Photo-Cross-Linking of Diketopyrrolopyrrole-Based Polymers with Polydiacetylenes toward Tunable Mechanical and Electronic Properties
Audithya Nyayachavadi, Amit K. Sur, Piumi Kulatunga, Yunfei Wang, Tiago Carneiro Gomes, Madison Mooney, Gage T. Mason, Anita Hu, Xiaodan Gu, Simon Rondeau‐Gagné
Abstract
A solvent-less and additive-free approach was developed for the cross-linking of π-conjugated polymers through the formation of polydiacetylene (PDA) cross-links. Different ratios of conjugation-breaking spacers incorporating 1,3-butadiyne motifs were inserted into semicrystalline diketopyrrolopyrrole-based polymers and reacted under UV light to trigger a topochemical photopolymerization. Upon photo-cross-linking, the formation of PDA cross-links was confirmed by Raman spectroscopy, and the resulting materials were further characterized through various techniques including Fourier transform infrared spectroscopy, atomic force microscopy, X-ray scattering, and UV–vis spectroscopy to evaluate their photophysical and optical properties. Furthermore, the mechanical properties of the PDA-containing semiconducting materials were evaluated via quantitative nanomechanical mapping, which confirmed that an increased cross-linking density rigidified the polymer network in thin films, leading to more brittle yet robust semiconductors. The incorporation of PDA cross-linking bridges across adjacent polymer chains was also shown to preserve the solid-state morphology, leading to uniform cross-linked thin films. Finally, the electronic properties of the cross-linked materials were investigated by the fabrication of organic field-effect transistors, which confirmed that the new cross-linking approach does not significantly alter the properties of the semiconducting materials. The novel cross-linking method for semiconducting polymers described is a promising approach for the processing of organic electronic materials and for the modulation of their thermomechanical properties, thus opening new avenues to design and develop solvent-resistant and rigid materials for emerging organic electronics.