α-Modified Naphthodithiophene Diimides—Molecular Design Strategy for Air-Stable n-Channel Organic Semiconductors

Abstract

Molecular modifications of naphtho[2,3-b:6,7-b′]dithiophene diimide (NDTI) by introducing electron-deficient substituents, such as p-(trifluoromethyl)phenyl-, 5-pyrimidyl-, and chlorine groups, on the thiophene α-positions were examined to develop superior n-channel organic semiconductors for organic thin-film transistors (OTFTs). Among newly developed NDTI derivatives, N,N′-dioctyl-2,7-dichloro-NDTI (5) was found to be a superior semiconductor over N,N′-dioctyl-NDTI (1a). The OTFTs based on 5 showed electron mobility as high as 0.73 cm2 V–1 s–1, whereas the mobility of α-unsubstituted 1a based OTFTs was 0.05 cm2 V–1 s–1. The improved mobility by the introduction of chlorine groups can be explained by the electronic structure in the solid state. In contrast to an one-dimensional (1D) electronic structure of 1a elucidated by single crystal X-ray analysis and theoretical calculations, 5 can be characterized as a two-dimensional (2D) bricklayer structure, in which the chlorine groups at the thiophene α-posit...