Synthesis and Characterization of New Thermally Stable Poly(naphthodithiophene) Derivatives and Applications for High Performance Organic Thin Film Transistors

Abstract

A series of new p-type polymers, PNDT-T and PNDT-TT, with enforced coplanar structure for effective pi-electron delocalization, having naphtho[2,1-b:3,4-b']-dithiophene and thiophenes as main core units, were successfully synthesized by Stille coupling reaction. The naphtho[2,1-b:3,4-b']dithiophene unit of the polymer main chain enhances charge carrier mobility by extending pi-conjugation length and rigidly enforced coplanar structure. Both polymers, PNDT-T and PNDT-TT, have high thermal stability up to 250 degrees C with a high T-g of 402 degrees C. On the basis of AFM and XRD results, it was found that PNDT-TT showed relatively more highly ordered intermolecular structures than did PNDT-T, with thiophene unit and high field-effect mobility, because the bithiophene unit provides crystallinity with increasing planarity and enough space for interdigitation of the long alkyl side chains for high order. These new p-type polymers PNDT-T and PNDT-TT exhibit high carrier mobilities of 0.01 and 0.076 cm(2)/(V s) and on/off ratios of 4 x 10(5) and 7 x 10(6), respectively. The above results indicate that the plate structure with a sulfur-containing fully aromatic system, which has the upper direction extended, could enhance the thermal stability and charge transport characteristics for OTFT applications.