Polymorphism-controlled charge transport in T-shaped π-conjugated crystals: high mobility via a double-column pathway

Abstract

Organic semiconductors offer a unique platform for developing flexible, lightweight, and low-cost electronic materials, where charge-transport properties are highly sensitive to molecular packing and polymorphism. Understanding how molecular geometry and orbital alignment govern intermolecular electronic coupling is essential for achieving high mobility and structural robustness. Here, we report the design of a novel T-shaped π-conjugated molecule engineered to promote cooperative electronic couplings between adjacent π-stacking columns in the solid state. Temperature-controlled physical vapor transport (PVT) yielded two distinct polymorphs: a low-temperature (LT) form with a θ-type packing motif and a high-temperature (HT) form adopting a pitched π-stacking arrangement analogous to rubrene. Despite its lower density, the HT form exhibits shorter π–π distances and abundant C–H⋯π interactions that promote favorable orbital phase alignment and strong electronic coupling between two parallel stacking columns. This pathway, termed “double-column transport,” constitutes a cooperative one-dimensional transport framework that enhances robustness against defects. Transfer-integral calculations predicted hole mobilities an order of magnitude higher for the HT form, and single-crystal transistor measurements confirmed this trend, yielding a maximum mobility of 1.2 cm² V⁻¹ s⁻¹. These findings demonstrate that charge-transport performance in polymorphic organic semiconductors is governed not by packing density but by orbital phase matching, establishing polymorph control and double-column transport design as effective strategies for realizing robust, high-mobility organic semiconductors.