Synthesis and Characterization of Pyrrolo[3,4-d] Pyridazine-5,7-Dione-Based Conjugated Polymers for Organic Thin-Film Transistors

Two new conjugated polymers, poly{6-(2-dodecylhexadecyl)-1,4-di(thiophen-2-yl)-5H-pyrrolo[3,4d] pyridazine-5,7(6H)-dione-alt-2,2'-bithiophene} (PPz-BT) and poly{6-(2-dodecylhexadecyl)-1,4di( thiophen-2-yl)-5H-pyrrolo[3,4-d] pyridazine-5,7(6H)-dione-alt-3,3'-dimethoxy-2,2'-bithiophene} (PPz-MeOBT), which contain methoxy-substituted and unsubstituted bithiophene units, respectively, were designed and synthesized. Experimental results revealed that the introduction of methoxy groups increases the highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels of the polymer because of the electron donating ability of the methoxy group and improves the planarity of the conjugated polymer backbone. However, the two-dimensional grazing incidence X-ray diffraction pattern of the PPz-MeOBT thin film reveals a bimodal structure, whereas the PPz-BT thin film shows a predominant edge-on orientation. As confirmed by X-ray analysis, after thermal annealing at 280 degrees C, top-gate/bottom-contact organic thin-film transistors fabricated with PPz-BT show a higher field-effect mobility (2x10-3 cm(2)V(-1)s(-1)) compared to those fabricated with PPz-MeOBT (4x10(-4) cm(2)V(-1)s(-1)).