Synthesis, properties, and photolithography of polythiophene derivatives

The focus of this work is the synthesis, properties, and photolithography of derivatives of pi-conjugated polythiophenes. Polymeric properties can be modified by chemically tailoring the thiophene monomer with various organic functional groups. Polythiophenes are attractive materials for electronic and optical device applications. Therefore, it is important to investigate their structure-property relationships, their photochemical stability, and to develop methodology for fabricating well-defined architectures of these materials.;All homopolymers and copolymers in this work were made by oxidative coupling of the appropriate monomer(s) using FeCl3. Poly(3-methoxythiophene-co-3-hexylthiophene) (P3MeOT-co-3HT) polymers were prepared and studied in relation to other polymers their film forming properties and stability in the oxidized state. Good uniform films could be cast from copolymers possessing low 3-methoxythiophene content. The stability of the oxidized copolymer in ambient light and air was greater than poly(3-hexylthiophene) (P3HT). The enhanced stability of the copolymer is attributed to the electron-donating oxygen atoms which stabilize the oxidized form.;The regiochemistry of poly[E-1,2-di(2'-(4 '-hexyl)thienyl)ethene] was prepared exhibiting a head-to-head conformation of the hexylthiophene dyads. 1H NMR and UV-visible measurements were used to confirm the structure of the oligomer and polymer.;Poly[3-(2'-methacryloyloxyethyl)thiophene] possesses a reactive side chain and was prepared by two routes: oxidative coupling of 3-(2'-methacryloyloxyethyl)thiophene and the reaction of methacryloyl chloride with poly [3-(2'-hydroxyethyl)thiophene] (P3HET). The irradiation dose required to entirely crosslink films of P3MET was determined to be lower than poly(3-hexylthiophene) by gel dose experiments.;Treatment of poly[3-(2'-acetoxyethyl)thiophene] (P3AcET) and P3HT with H2SO4 was investigated. UV-visible and electronic conductivity measurements showed that P3AcET was oxidized by acid treatment. P3HT was oxidized to a much lesser extent under the same conditions because of its hydrophobic nature. Acid-treated P3AcET was neutralized and the product was identified as poly[3-(2'-hydroxyethyl)thiophene]. The pendent hydroxy groups on MET could be reacted with acid chlorides illustrating that the polymer can be functionalized past polymerization.;Polythiophene derivatives were made highly conducting by treatment with either FeCl3, AuCl3, I2, or H2SO 4. Oxidized films exposed to ambient light and air showed a loss in conductivity. The life-time of the conductivity was dependent upon the stability of oxidizing agent used.;The photochemistry of films of polythiophene derivatives in ambient air was monitored with FTIR and UV-visible spectroscopy. Spectra of the polymers revealed evidence of photooxidation and photobleaching. The films were also rendered insoluble in organic solvents by photo-induced crosslinking of the copolymers.;Conventional photolithography was used to pattern images of polythiophene derivatives with micron resolution. Poly(3-methoxythiophene-co-3-hexylthiophene) and poly[E-1,2-di(2'-(4'-hexyl)thienyl)ethene] were photoimaged using polychromatic light (>300 nm). Patterns of poly[3-(2 '-methacryloyloxyethyl)thiophene] were generated using lower irradiation doses. In contrast, P3AcET was imaged by chemical modification without direct irradiation of the pi-conjugated polymer.