Incorporation of Selenopheno[3,2-b]pyrrole into Benzothiadiazole-Based Small Molecules for Organic Field-Effect Transistors

Incorporating selenophene into organic semiconductors has recently shown promising results in both organic solar cells (OSCs) and organic field-effect transistors (OFETs). In most studies, replacing thiophene with selenophene has improved the performance in OSCs and OFETs. However, some other reports do not show the same trend. Therefore, the structure–property relationship of selenophene-containing semiconducting materials is still to be investigated and understood. On the other hand, reports have shown that thiophene flanked benzothiadiazole- and thieno[3,2-b]pyrrole-based donor–acceptor–donor molecular architecture gave a banana-shaped small organic conjugated molecule with moderate OFETs performance. To understand the structure–property relationship and influence on OFETs performance, by replacing thiophene with selenophene in chalcogenopheno[3,2-b]pyrrole, we report a nonconventional fused ring system, ester-monocapped selenopheno[3,2-b]pyrrole, which was coupled with chalcogenophene spacer flanked benzothiadiazole to yield two curved small organic conjugated molecules, diethyl 2,2′-(5,5′-(benzo[c][1,2,5]thiadiazole-4,7-diyl)bis(thiophene-5,2-diyl))bis(4-dodecyl-4H-selenopheno[3,2-b]pyrrole-5-carboxylate (BT-2T-2SeP) and diethyl 2,2′-(benzo[c][1,2,5]thiadiazole-4,7-diylbis(selenophene-5,2-diyl))bis(4-dodecyl-4H-selenopheno[3,2-b]pyrrole-5-carboxylate (BT-2Se-2SeP). This is the first report of selenopheno[3,2-b]pyrrole incorporated in donor–acceptor small conjugated organic molecules for OFETs applications. BT-2T-2SeP and BT-2Se-2SeP exhibited comparable maximum hole mobilities of 8.82 × 10–3 cm2 V–1 s–1 and 1.44 × 10–2 cm2 V–1 s–1, respectively. Furthermore, these molecules exhibited lower threshold voltages between 0-(−5) V and high on–off current ratios of 104 and ∼105, respectively, for BT-2T-2SeP and BT-2Se-2SeP.