Pyrrole is an excellent building block for the synthesis of organic semiconductors. However, the synthesis of pyrrole organic semiconductors is challenging because pyrroles are prone to oxidation. The smallest S, N-heteroacene, thieno[3,2-b]pyrrole is a good building block for organic semiconductors due to its electron density, asymmetry, and easily modifiable NH group. Recently we showed that organic semiconductors from thieno[3,2-b]pyrrole display “nearly-ideal” OFET characteristics without compromising charge carrier mobilities or threshold voltages. [1] We have varied the structure and topology to investigate the relatively under-explored banana shape thieno[3,2-b]pyrrole ole semiconductors and the influence of the heteroatom. Banana-shaped donor-acceptor molecules with benzothiadiazole, fluorinated benzothiadiazole acceptors, and thieno[3,2-b]pyrrole donor (TP-BT2T-BT and TP-FBT2T-TP) have been reported by our group, 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 the molecule (TP-BT2T-BT) with benzothiadiazole as the acceptor. The molecule containing fluorinated benzothiadiazole (TP-FBT2T-BT) showed hole mobility of 1.57×10-3 cm2 V-1 s-1. Lengthening conjugation by synthesizing conjugated polymers was employed to facilitate hole transport and to obtain comparatively stable semiconductors. Our group reported the donor-acceptor polymer containing thienopyrrole donor and diketopyrrolopyroole acceptor, P(DPP-TP) (Figure 1), and the OFET parameters were evaluated with bottom-gate/top-contact (BGTC) OFET architecture. An increase in hole mobility to 0.12 cm2 V-1 s-1 was observed for the polymer (P(DPP-TP)) as compared to the conjugated small molecules.

Pyrrole-based organic semiconducting materials for organic electronics applications

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