Novel Ladder π-Conjugated Materials-Sila-Pentathienoacenes: Synthesis, Structure, and Electronic Properties

A novel series of ladder pi-conjugated materials-sila-pentathienoacenes (Si-PTA) are synthesized and characterized. Crystal structures of the compounds show that the length of alkyl chains substituting on the thiophene ring has a significant influence on molecular packing. A densely packed structure with an interfacial distance of about 3.66 angstrom between the adjacent molecules is observed for the compound with shorter alkyl chains. However, a large interfacial distance (7.99 angstrom) is obtained for another compound because of the insertion of long alkyl chains between two planes. The investigation of the optical and electrochemical properties shows that the silylene bridge incorporated into the pentathienoacene framework exerts a clear effect on the electronic properties by the sigma*-pi* conjugation. Although only a slight enhancement is observed for the HOMO levels, with respect to that of pentathienoacene, the LUMO levels are significantly lowered. The observed electronic properties are consistent with the theoretical calculations.