Synthesis of Alternating Donor–Acceptor Ladder-Type Molecules and Investigation of Their Multiple Charge-Transfer Pathways

We describe the synthesis as well as the optical and charge-transport properties of a series of donor–acceptor (D-A) ladder-type heteroacenes. These molecules are stable, soluble, and contain up to 24 fused rings. Structural analyses indicated that the backbones of S 10r and Se 10r are bent in single crystals. The three 10-ring heteroacenes were functionalized with thiol anchoring groups and used for single-molecular conductance measurements. The highest conductance was observed for molecular wires containing a benzoselenadiazole (BSD) moiety, which exhibits the narrowest band gap. Multiple charge-transport pathways were observed in molecular wires containing either benzothiadiazole (BTD) or BSD. The conductance is a complex function of both energy gap and orbital alignment.