Conjugated Donor-Acceptor Polymers Entailing Pechmann Dye-Derived Acceptor with Siloxane-Terminated Side Chains Exhibiting Balanced Ambipolar Semiconducting Behavior

We present four conjugated donor-acceptor (D-A) polymers PBPDT-Si, PBPDSe-Si, PBPDT, and PBPDSe entailing a new electron acceptor Pechmann dye framework, i.e., bipyrrolylidene-2,2'(1H,1'H)-dione (BPD), and thiophene and selenophene as the respective electron donors. PBPDT-Si and PBPDSe-Si contain siloxane-terminated side chains, while PBPDT and PBPDSe bear branching alkyl chains. The respective HOMO energies of PBPDT-Si and PBPDSe-Si are slightly higher than those of PBPDT and PBPDSe, whereas the respective LUMO energies of PBPDT-Si and PBPDSe-Si are slightly lower than those of PBPDT and PBPDSe. The results reveal that (i) thin films of all four polymers show ambipolar semiconducting performances under a nitrogen atmosphere, (ii) hole and electron mobilities are more balanced for PBPDT-Si and PBPDSe-Si, and (iii) the employment of siloxane-terminated side chains is beneficial for improving charge transporting compared to branching alkyl side chains. Thin film hole and electron mobilities of PBPDT-Si can reach 0.74 and 0.87 cm(2) V-1 s(-1), respectively.