Effects of bromination on anthryl-capped DPP-based semiconductor materials: Improved electrical characteristics of organic field-effect transistors

Diketopyrrolopyrrole (DPP), typically flanked with thiophene rings as π-spacers, has been regarded as a promising electron-acceptor unit for constructing donor-acceptor-donor (D-A-D) type small molecule organic semiconductors. Exploring the relationships between its conjugation structure and semiconducting property is of great importance for both molecular design and device fabrication of such DPP materials. Herein we describe the synthesis, self-assembly, and transistor characteristics of two novel N- and N′− 2-octyldodecylated DPP derivatives which were modified with native anthracene (An) and brominated anthracene (Br-An) at 5-, 5′-position of the flanked thiophenes, respectively, namely An-DPP and Br-An-DPP. Attributing to the self-assembly behaviors, they exhibit enormous difference in hole transport characteristics on interdigitated-electrode based organic field-effect transistor (OFET) devices even though there is only two atoms’ discrepancy in accordance with their molecular structures. The characterization of OFETs with interdigitated-electrodes based on Br-An-DPP reveals p-channel operation with highest field-effect mobility of 0.2 cm²·V⁻¹·s⁻¹, which is 10⁷ times higher than that of An-DPP (4.8 × 10⁻⁸ cm²·V⁻¹·s⁻¹), and with a threshold voltage of - 2.5 V. X-ray diffraction, atomic force microscopy, scanning electron microscopy, and optical absorption studies reveal the presence of crystalline films caused by bromination on anthracene-modified alkylated DPP (i.e., Br-An-DPP), while An-DPP exhibits completely amorphous phase.