Chlorination-Assisted Isomerically Pure Oxindole-Terminated Quinoids for n-Type Organic Thin-Film Transistors.

Quinoidal compounds have great potential utility as high-performance organic semiconducting materials because of their rigid planar structures and extended π-conjugation. However, the existence of E and Z isomers adversely affects the charge-transport properties of quinoidal compounds. In this study, we developed three isomerically pure oxindole-terminated quinoids by introducing chlorine atoms in the quinoidal core. The synthesized quinoids were confirmed to have a Z,Z configuration by means of 1H NMR spectroscopy, density functional theory calculations, and single-crystal X-ray analysis. Importantly, the strategy of chlorination allowed to maintain low-lying frontier molecular orbital energy levels and ensure favorable intermolecular packing. Consequently, all three quinoidal compounds showed n-type transport characteristics in organic thin-film transistors, with electron mobilities up to 0.35 cm2 V-1 s-1, which is the highest value reported to date for oxindole-terminated quinoids. We believe that our study can provide new guidelines for the design of isomerically pure quinoids with high electron mobilities.