Manikandan Jayaraman

The first synthesis and new properties of regioregular, head-to-tail coupled polythiophenes

Abstract The preparation of polythiophene derivatives with essentially 100% head-to tail (HT) couplings leads to new defect free polythiophenes. These new HT polythiophenes formed self-oriented three dimensional structure with greatly enhanced two dimensional conductivity. Presented are the synthetic method developed in our lab, the new HT-polythiophenes prepared by our method, and the preliminary physical properties of these conducting polymers. Our results show that the structure and properties of HT-substituted polythiophenes are quite sensitive to the side chains attached to the polymers backbone.

Synthesis and physical properties of regiochemically well-defined, head-to-tail coupled poly(3-alkylthiophenes)

Abstract We have recently developed a regiospecific synthetic method that produces poly(3-alkylthiophenes) (PATs) that, for the first time, contain almost exclusively head-to-tail (HT) couplings [1]. Details on the synthesis, NMR characterization of structural regularity, UV-VIS data on solutions and thin films, and preliminary X-ray, electrical conductivity, and thermal data are presented herein. NMR spectral characterization reveals >93% head-to-tail-head-to-tail (HT-HT) couplings in poly(3-butylthiophene) (PBT), poly(3-hexylthiophene) (PHT), poly(3-octylthiophene) (POT), and poly(3-dodecylthiophene) (PDDT). In the UV-VIS, these PATs show lower energy absorption maximum shifts of up to 14 nm in solution, 46 nm in the solid state, and other intense lower energy peaks with shifts of up to 129 nm (609 nm) from PATs prepared by the usual methods. X-ray analysis of unoriented (as cast) thin films of PHT on glass indicate a much more ordered structure than PHT made from FeCl 3 . It also appears that our unoriented PHT is at least as ordered as stretch oriented PHT. Preliminary maximum room temperature electrical conductivity values for PATs (doped with I 2 ) are 1000 S cm −1 for PDDT, 200 S cm −1 for POT, and 60 S cm −1 for PHT. Thermal analysis of POT prepared by this method is also presented and these samples are found to be highly crystalline.

Directed self-assembly of amphiphilic regioregular polythiophenes on the nanometer scale

Regioregular polythiophenes possessing alternating hydrophobic and hydrophilic substituents have been synthesized and fully characterized. The amphiphilic nature of the polymer allows it to assemble at the air-water interface forming highly ordered domains. Directed self-assembly of the resulting conducting monolayer into a microelectronic chip structure is described.

Saturation effects in the nonlinear optical response of regioregular, highly conjugated poly(3-alkyl-thiophene) thin films

Abstract Third harmonic generation measurements on highly conjugated regioregular poly(3-dodecylthiophene) thin films using a fundamental wavelength of 1907 nm give an absolute value of χ(3)(-3ω;ω,ω,ω) = 4×10−11 esu. This value is the nonlinear susceptibility of the most highly conjugated polythiophene film reported to date (λmax= 555 nm). Comparison to less conjugated samples reveals a saturation in the dependence of χ(3) the effective conjugation length.

The tuning of conjugation by recipe: the synthesis and properties of random head-to-tail poly(3-alkylthiophene) copolymers

Regioregular head-to-tail coupled poly(3-alkylthiophene) random copolymers have been synthesized and show that the conjugation can be tuned by variation of the length and relative ratios of alkyl side chains.