The Polymer Society of Korea

Abstract

In this study, we present a multiscale modeling framework—coupling Density Functional Theory (DFT), a newly optimized force field (FF), and atomistic Molecular Dynamics (MD)—to elucidate how side chains govern solid-state structures. We optimize both nonbonded and bonded interaction parameters of FF against DFT data. The new FF reduces the errors in binding energies significantly compared to the Dreiding FF. With this FF, we demonstrate, using solid-state MD simulations, that PBTTT backbones planarize in contrast to gas-phase DFT predictions, resulting in more enhanced structural organization in comparison to PBnDT-FTAZ. This is attributed to the superior structural development of side chains in PBTTT. Finally, we capture the thermal evolution of PBTTT. In particular, our simulations show that annealing above 125 °C re-orients side chains and promotes backbone planarity, thereby identifying a dominant mechanism of thermal transitions. Together, these results offer broadly applicable design principles toward the rational design and controlled solid-state assembly for polymer semiconductors.