Variation of aggregated structures driven by side chains is a crucial issue in organic semiconductors (OSCs) for achieving high carrier mobility and device durability. In this work, phenylalkyl side chains composed of a rigid terminal phenyl group and a flexible alkyl linker were studied based on a state-of-the-art n-type π-electron system, 3,4,9,10-benzo[de]isoquinolino[1,8-gh]quinolinetetracarboxylic diimide (BQQDI), from the viewpoints of aggregated structures and thin-film transistors. An appropriate length of the alkyl, i.e., propyl, linker led to stable formation of a unique aggregated structure regardless of solution-grown single-crystal and vacuum-deposited polycrystalline thin films likely due to cooperation of rigid phenyl and flexible alkyl moieties. In contrast, a shorter ethyl linker showed polymorphism in the polycrystalline film. An absence of polymorphism did not only result in high mobility and low threshold voltage but also show low contact resistance. Hence, this work proposes opportunities to design n-type OSCs by introduction of both rigid and flexible characters to the side chains.
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