New Semiconducting Polymers Containing 3,6-Dimethyl(thieno[3,2-b]-thiophene or selenopheno[3,2-b]selenophene) for Organic Thin-Film Transistors

A series of new organic Semiconducting polymers containing the fused aromatic rings 3,6-dimethylthieno[3,2-b]thiophene or 3,6-dimethylselenopheno[3,2-b]selenophene as core units were successfully synthesized via oxidative coupling reactions. These core units have the adva3ntage of requiring one-step synthesis. Two polymers containing these core units, poly(2,5-bis(3-dodecylthiophen-2-yl)-3,6-dimethylthieno[3,2-b]thiophene) (PmT) and poly,(2,2'-(3,6-dimethylselenopheno[3,2-b]selenophene-2,5-diyl)bis(3-dodecylthiophene)) (PmSe), exhibited very poor thin-film transistor (TFT) performances because of the distortion of the core units caused by inter- and intramolecular repulsion between long dodecyl side chains and methyl chains attached to the core units, In contrast, poly(2,5-bis(3'-dodecyl-2,2'-bithiophen-5-yl)-3,6-dimethylthieno[3,2-b]thiophene) (PTmT) and poly(5,5 ''-(3,6-dimethylselenopheno[3,2-b]selenophene-2,5-diyl)bis(3-dodecyl-2,2'-bithiophene)) (PTmSe) contain additional unsubstituted thiophene rings next to the fused aromatic core units. PTmT and PTmSe exhibited much more ordered intermolecular Structures than PmT and PmSe because the unsubstituted thiophene rings diminish the distortion of the core units caused by the repulsion of the methyl chains attached to the fused aromatic ring and enable intermolecular interdigitation of the dodecyl side chains of neighboring polymer main backbones. Because of the improved intermolecular ordering, PTmT and PTmSe exhibited relatively high performance in field effect transistors, The carrier mobilities (mu) or these polymers were 0.03-0.04 cm(2) V-1 s(-1) with an on/off ratio of approximately 10(6), that is TFT performance parameters that are remarkably better than those of PmT (mu = 8.1 x 10(-7) cm(2) V-1 s(-1)) and PmSe (mu = 6.4 x 10(-6) cm(2) V-1 s(-1)). In addition, PTmT and PTmSe devices exhibited good thermal stability. Thus, control of the core units is very important in the design of semiconducting polymers with well ordered intermolecular packing for achieving high performance TFTs.