Oligothiophenes with the naphthalene core for organic thin-film transistors: variation in positions of bithiophenyl attachment to the naphthalene

•The most planar and conjugated derivative afforded remarkably high hole mobility.•Hole mobility of twisted derivatives doesn’t follow order of molecular band gaps.•Molecular symmetry is believed to play an important role for effective molecular packing.

Relationship between molecular structure of organic material and its semiconducting properties is far from being trivial. Hence, a complex study based on systematic variation of molecular structure can contribute to understanding of this relationship. Herein we describe the synthesis, characterization and field-effect transistor (OFET) properties of a consistent series of naphthalene derivatives with hexylbithiophenyl chains attached at positions 1 and 4 (H2T14N), 1 and 5 (H2T15N), and 2 and 6 (H2T26N). The almost planar derivative H2T26N with the narrowest HOMO-LUMO band gap has good film forming ability, resulting in the remarkably high hole mobility (0.12 cm2 V−1 s−1). Although both the H2T14N and H2T15N derivatives have almost the same twist of thiophene unit from the naphthalene plane, the latter has weaker conjugation between the bithiophenyl arms but exhibited higher charge mobility (0.016 cm2 V−1 s−1). Apparently, a proper combination of molecular structure prerequisites and film-forming properties of semiconducting molecular material is essential for good OFET performance. It has been shown that also molecular symmetry can play an important role for effective two-dimensional molecular packing of the organic material.

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