(698f) Self-Assembly of Donor-Acceptor Conjugated Polymer in the Condensed Phase

Organic electronic materials have many desirable properties such as flexibility, ease of tunability, and low-cost solution processibility. Among organic semiconductors, donor-acceptor conjugated polymers (DACPs) have drawn a greater attraction due to the easy tunability of the band-gap. The performance of the semiconductor devices is highly dependent on the self-assembly of the thin polymer films. Although several studies have been performed to understand the self-assembly of DACPs in the condensed phase, atomic level interaction that controls self-assembly is not clearly understood. One of the most important factors that control the charge transfer in the self-assembled thin film is the π-stacking between polymer chains. π-stacking orientation also determines the device type, such as – edge-on orientation is preferable for transistor-like devices, and the face-on orientation is suitable for photovoltaic devices. In this work, cyclopentadithiophene (donor) – benzobisthiadazole (acceptor) (CPDT-BBT), which shows a high-spin ground state electronic configuration, is considered as a prototypical DACP in chloroform solvent. CPDT-BBT shows distinct magnetic properties and a lower band-gap with a broader wavelength absorption near-infrared (NIR). Here, we examine the effects of oligomer chain-length, side-chain, and processing temperature on self-assembled π-stacking, with molecular dynamics (MD) simulation. We find that the oligomer chains with staircase π-stacking pattern display extended configurations in the solution and around 3.40 Å π-stacking distance. We also show details of the local solvation of these polymeric chains through careful structural analysis.