Forming Long-Range Order in Solution-Processed Semiconducting Polymers

Intermolecular interactions control molecular dissolving and stacking through directional solution processes, which determine the thin-film morphologies. While directional solution processes have been widely used, their resulting morphologies are often disordered or ordered in small scale, making their electronic characterizations unreliable. To overcome this issue, ordered structures created by regulating complex intermolecular interactions is required. This study aims to quantitatively identify and control the intermolecular interactions between semiconducting polymers and self-assembled monolayers (SAMs) in solutions to achieve long-range order. The proposed methodology of intermolecular guidance involves optimizing the processing temperature for dissolving aggregates into shorter bundles, finding their guidable intermolecular scale, and then guiding them along 1D nano-templated SAMs to form unidirectional fibers. The validity of this methodology is confirmed by various spectroscopic and morphologic techniques, demonstrating highly-ordered molecular stacking in unidirectional fabric structures. Based on Flory-Huggins theory and our experiments, the critical intermolecular scale and energy of the guidance and ordering are confirmed to be about 3 Å and 40 meV. In this range, small and random aggregates can be aligned to form macroscopically-ordered fibers, showing an increase in anisotropic Raman scattering intensity from around 1 to 10. Overall, this work provides a quantitative guideline to control complex intermolecular interactions of dissolving, stacking, and ordering between semiconducting polymers and self-assembled monolayers, showing the angstrom-scale controllability in molecular assembly.