Controlling backbone conformation of rigid-rod-like liquid-crystalline conjugated polymer PBTTT- C14 via fluorine-based surface passivation

Abstract

In conjugated polymers, it is challenging to realize a rigid coplanar conformation without involving complex and judicious molecular level design and synthesis. In this work, we demonstrate planarization of the backbone of a thiophene-based liquid crystalline conjugated polymer PBTTT-C14 thin films fabricated by unidirectional floating film transfer method (U-FTM) on fluoropolymer-based surface passivated substrates. The U-FTM fabricated thin films are known to exhibit good optical anisotropy with edge-on orientation. Annealing PBTTT-C14 film at its mesophase on fluorine-rich CYTOP reduced the torsional disorder in the conjugated backbone, which resulted in extension of conjugation length and improved crystallinity, showcasing a significant band edge red-shift of 25 nm, peak shift of 16 nm in the absorption spectra. The increased interdigitation of alkyl chains and stacking with edge-on orientation is utilized in conducting polymer-based organic field-effect transistors (OFETs) and achieved a high mobility of 0.16 cm2/V.s. Copyright © 2026. Published by Elsevier B.V.