Synthesis and n‐Type Semiconducting Properties of Bis(dioxaborin) Compounds Containing a π‐Extended 2,2′‐Bithiophene Structure

Abstract

Bis(dioxaborin) compounds containing π‐conjugated systems have been studied as n‐type semiconductors for organic field‐effect transistors (OFETs). In this study, with the aim of investigating the effect of the extension of the π‐conjugation on the n‐type semiconducting properties and stability of bis(dioxaborin) compounds, we synthesized new compounds containing 2,2′‐bithiophene derivatives extended with an olefin or an acetylene spacer. The absorption maxima of the compounds containing olefin spacers were greatly red‐shifted compared with those of the original compound without a π‐spacer. The newly synthesized compounds exhibited high electron affinity, and the olefin spacers effectively reduced the on‐site Coulomb repulsion in the two‐electron reduction of the compounds. An OFET fabricated using one of these compounds having a layer‐by‐layer crystal structure exhibited n‐type semiconductor behavior with a low threshold voltage, most likely due to the small on‐site Coulomb repulsion. The electron‐transporting properties were investigated by theoretical calculations based on the Marcus theory.