π-Extended Thiadiazoles Fused with Thienopyrrole or Indole Moieties: Synthesis, Structures, and Properties

We report the syntheses, structures, photo-physical properties, and redox characteristics of donor-acceptor-fused pi-systems, namely pi-extended thiadiazoles 1-5 fused with thienopyrrole or indole moieties. They were synthesized by the Stille coupling reactions followed by the PPh3-mediated reductive cyclizations as key steps. X-Ray crystallographic studies showed that isomeric 1b and 2b form significantly different packing from each other, and la and 4a afford supramolecular networks via multiple hydrogen bonding with water molecules. Thienopyrrole-fused compounds lb and 2b displayed bathochromically shifted intrarnolecular charge-transfer (CT) bands and low oxidation potentials as compared to indole-fused analog 3b and showed moderate to good fluorescence quantum yields (Phi(f)) up to 0.73. In 3b-5b, the introduction of electron-donating substituents in the indole moieties substantially shifts the intramolecular CT absorption maxima bathochromically and leads to the elevation of the HOMO levels. The Phi(f) values of 3-5 (0.04-0.50) were found to be significantly dependent on the substituents in the indole moieties. The OFET properties with lb and 2b as an active layer were also disclosed.