Siloxane Side-Chain-Modified Diketopyrrolopyrrole and Thienopyrrole Containing Small Molecules for Organic Field-Effect Transistors

Thieno[3,2-b]pyrrole (TP) is a donor moiety employed in organic semiconducting small molecules and polymers. Among the TP-containing small molecules reported, benzo[c]-[1,2,5]thiadiazole (BT) acceptor-based donor-acceptor (DA) type molecules have shown mobilities of similar to 0.1 cm2 V-1 s-1. In this study, we are reporting the synthesis, characterization, and testing of the organic field-effect transistor (OFET) performance of two donor- acceptor-donor (DAD) type small molecules with TP donors and siloxane-functionalized diketopyrrolopyrrole (DPP) acceptors, namely, diethyl 2,2 '-((2,5-bis(6-(1,1,1,3,5,5,5-heptamethyl-trisiloxan-3-yl)hexyl)-3,6-dioxo-2,3,5,6-tetrahydropyrrolo [3,4-c]- pyrrole-1,4-diyl)bis(thiophene-5,2-diyl))bis(4-methyl-4H-thieno-[3,2-b]pyrrole-5-carboxylate (DPP-2T-2TP) and diethyl 2,2 '-((2,5-bis(6-(1,1,1,3,5,5,5-heptamethyltrisiloxan-3-yl)hexyl)-3,6-dioxo-2,3,5,6 tetrahydropyrrolo[3,4-c]pyrrole-1,4-diyl)bis(furan-5,2-diyl))-bis(4-methyl-4H-thieno[3,2-b]pyrrole-5-carboxylate (DPP-2F-2TP). The difference between DPP-2T-2TP and DPP-2F-2TP is the spacer between the donor and acceptor. According to a few reports, siloxane-containing side chains were known to provide stability in ambient conditions in OFETs compared to their alkyl-substituted analogs. In this study, siloxane side-chain-substituted small molecular OFETs were fabricated, annealed, and tested under ambient conditions. Both molecules showed OFET activity with a maximum hole mobility of 4.10 x 10-2 cm2 V-1 s-1 (DPP-2T-2TP) and 6.40 x 10-5 (DPP-2F-2TP) cm2 V-1 s-1 in ambient conditions, where thiophene spacer containing DPP-2T-2TP had a better performance.