Pyrrole is an excellent building block for the synthesis of organic semiconductors. The smallest S, N-heteroacene, thieno[3,2-b]pyrrole is a good building block for organic semiconductors due to its electron density and easily modifiable NH group. Recently we demonstrated that organic semiconductors from thieno[3,2-b]pyrrole (TP) display “nearly-ideal” OFET characteristics without compromising charge carrier mobilities or threshold voltages. We have varied the structure and topology to investigate the relatively under-explored banana shape thieno[3,2-b]pyrrole semiconductors. Banana shaped donor-acceptor molecules with benzothiadiazole (BT) acceptors and thieno[3,2-b]pyrrole (TP-BT2T-BT) have been reported by our group (Figure 1a), and the OFET parameters were evaluated in a bottom-gate/bottom-contact (BGBC) OFET architecture. Hole mobility of 0.08 cm2 V-1 s-1 was measured for TP-BT2T-BT with benzothiadiazole as the acceptor. Compared to TP, the selenopheno[3,2-b]pyrrole (SeP) donor is a relatively electron-rich block that is capable of providing more electron density into hole-transporting semiconducting materials. Therefore, replacing TP with SeP has a great potential to improve the hole-transporting properties of the BT based small molecules. In this study, SeP and BT based small molecules with selenophene (SeP-BT2Se-SeP; Figure 1c) and thiophene (SeP-BT2T-SeP; Figure 1b) spacers are investigated for OFET activity and properties. Selenopyrrole and thienopyrrole spacers are selected to systematically study the effect of the heteroatom's size on the spacer and obtain well-conjugated coplanar backbone structures that facilitate better charge transfer and molecular packing. To understand the structure-property relationship, optoelectronic properties and OFET properties of the SeP-based small molecules are compared with each other and TP-BT2T-BT.

Pyrrole-based organic semiconducting small molecules for organic field-effect transistors

ACS Spring Meeting 2021

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