Engineering solvent resistance in semiconducting polymer films through UV-induced polydiacetylene crosslinking.

Semiconducting polymers have emerged as versatile, tunable materials for next-generation optoelectronic devices, offering advantages over traditional inorganic semiconductors in applications from energy harvesting to bioelectronics. Particularly, their compatibility with scalable manufacturing techniques, including solution-based deposition and printing methods, positions them favorably for commercial adoption. Among the recent strategies used to enhance the mechanical, thermal, and electronic properties of these polymers, crosslinking-through covalent or non-covalent interactions-has been shown to be especially efficient for improving their stability, robustness, and functionality. Notably, crosslinking can also confer solvent resistance to these materials, a crucial feature for multilayer device fabrication that can help to maintain layer integrity during sequential printing processes. In this work, we synthesized a diketopyrrolopyrrole-carbazole conjugated copolymer functionalized with 1,3-butadiyne groups on the carbazole side chains, enabling covalent crosslinking UV-induced topochemical polymerization into polydiacetylene (PDA) networks. Raman spectroscopy confirmed PDA crosslink formation, while atomic force microscopy and grazing incidence wide-angle X-ray scattering were used to demonstrate the preservation of polymer film morphology post-crosslinking. Quantitative nanomechanical mapping revealed significant enhancements in mechanical properties upon PDA formation. Additionally, sequential deposition and crosslinking cycles demonstrated the robust solvent resistance of crosslinked films, confirmed by UV-vis spectroscopy. These results highlight topochemical polymerization of diacetylenes as an effective strategy for engineering mechanically robust, solvent-resistant conjugated polymer films suitable for advanced multilayer organic electronics.