Charge Carrier Polarity Modulation in Diketopyrrolopyrrole-Based Low Band Gap Semiconductors by Terminal Functionalization

Abstract

Organic semiconductors with variable charge carrier polarity are required for optoelectronic applications. Herein, we report the synthesis of three novel diketopyrrolopyrrole (DPP)-based D–A molecules having three different terminal groups (amide, ester, and dicyano) and study their electronic properties. An increase in electron acceptor strength from amide to dicyano leads to a bathochromic shift in absorption. Photoconductivity and field effect transistor (FET) measurements confirmed that a small increase in acceptor strength can result in a large change in the charge transport properties from p-type to n-type. The molecule with an amide group, DPP–amide, exhibited a moderate p-type mobility (1.3 × 10–2 cm2 V–1 s–1), whereas good n-type mobilities were observed for molecules with an ester moiety, DPP–ester (1.5 × 10–2 cm2 V–1 s–1), and with a dicyano group, DPP–DCV (1 × 10–2 cm2 V–1 s–1). The terminal functional group modification approach presented here is a simple and efficient method to alter the charge carrier polarity of organic semiconductors.