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

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.