Donor-Acceptor Conjugated Polymers Based on Dithieno[3,2-b:3′,2′-b]naphtho[1,2-b:5,6-b′]dithiophene: Synthesis and Semiconducting Properties

A polycyclic aromatic unit comprising six rings, i.e., 5,11-bis(2-octyldodecyl)dithieno[3,2-b:3',2'-b']naphtho[1,2-b:5,6-b']dithiophene (DTNDT), was developed. Four donor-acceptor (D-A) conjugated polymers, which are named P-BT, P-2FBT, P-IID, and P-DPP, were synthesized with DTNDT as the D-unit and 2,1,3-benzothiadiazole (BT), 5,6-difluorobenzo[c][1,2,5]thiadiazole (2FBT), isoindigo (IID), and diketopyrrolopyrrole (DPP) as the A-unit, respectively. All four polymers are thermally stable with decomposition temperature above 390 degrees C and show pseudo-straight-shaped backbones. Their ordered thin films were prepared via solution spin-casting, in which conjugated backbones mainly adopted edge-on alignment on the substrate. The semiconducting properties of the polymers were characterized with bottom gate and top contact (BGTC) organic thin film transistors (OTFTs). All four polymers showed p-type transport behavior, and the hole mobilities were 0.023, 0.078, 0.50, and 1.80 cm(2)/(V s) for P-BT, P-2FBT, P-IID, and P-DPP, respectively. P-DPP exhibited the highest film order, a short pi-pi stacking distance (3.52 angstrom), and therefore the highest device mobility.