N-type field-effect transistors based on layered crystalline donor–acceptor semiconductors with dialkylated benzothienobenzothiophenes as electron donors†
We report the structural, electronic, and field-effect transistor characteristics of a series of molecular donor–acceptor charge-transfer (CT) compounds composed of 2,7-dialkylbenzothieno[3,2-b]benzothiophenes (diCn-BTBT; n = 4, 8, and 12) as donors and optionally fluorinated derivatives of tetracyanoquinodimethane (FmTCNQ; m = 0, 2, and 4) as acceptors. (diCn-BTBT)(FmTCNQ) form isomorphous layered crystalline structures consisting of alternating π-conjugated layers and alkyl chain layers, irrespective of the length of the alkyl chains. The compounds exhibit unique double-peaked CT absorption-band features that are polarized along the donor–acceptor interaction. Field-effect transistors based on these single crystals show a relatively high field-effect mobility (0.4 cm2 V−1 s−1), the p- and n-type operation of which can be tuned by altering the fluorine substitution in TCNQ.