Benzothiadiazole-Dithienopyrrole Donor–Acceptor–Donor and Acceptor–Donor–Acceptor Triads: Synthesis and Optical, Electrochemical, and Charge-Transport Properties

2,2′-(Benzo[c][1,2,5]thiadiazol-4,7-diyl)-4,4′-dialkyl-bis(4H-dithieno[3,2-b:2′,3′-d]pyrrole) (DTP-BTD-DTP) donor–acceptor–donor (D-A-D) and 4-alkyl-2,6-bis(benzo[c][1,2,5]thiadiazol-4-yl)-4H-dithieno[3,2-b:2′,3′-d]pyrrole (BTD-DTP-BTD) acceptor–donor–acceptor (A-D-A) triads, with or without additional alkylation in the DTP 6- or BTD 7-positions, respectively, have been synthesized using Stille coupling reactions, characterized using UV–vis absorption spectroscopy and electrochemistry, modeled using density functional theory calculations, and used as charge-transport materials in field-effect transistors. The choice of alkyl substitution pattern has only minor effects on the optical and redox behavior but can be used to modify the thermal properties and solubility of these compounds. The D-A-D and A-D-A triads show long-wavelength absorption maxima at 566–588 and 517–521 nm, respectively, in solution. These transitions are attributed to excitation from a delocalized HOMO to a BTD-localized LUMO and, accor...