An investigation of the new synthetic method to synthesize regioregular, head-to-tail coupled poly(3-alkylthiophenes) using magnesium−halogen exchange (Grignard metathesis) called the GRIM method is described. Treatment of 2,5-dibromo-3-alkylthiophenes with a variety of alkyl and vinyl Grignard reagents resulted in two metalated, regiochemical isomers, namely, 2-bromo-3-alkyl-5-bromomagnesiothiophene and 2-bromomagnesio-3-alkyl-5-bromothiophene in an 85:15 ratio. This ratio appears to be independent of reaction time, temperature, and Grignard reagent employed. Introduction of a catalytic amount of Ni(dppp)Cl2 to this isomeric mixture afforded poly(3-alkylthiophene) that contained greater than 95% HT−HT couplings (typically 98% HT couplings were seen). The high degree of regioregularity found in the polymer can be explained by a combination of kinetic and thermodynamic effects arising from steric and electronic effects found in the catalytic reaction. A series of reaction investigations led to a general explanation of the origin of regioregularity in polythiophene polymerization reactions. These reactions included kinetic studies and competition experiments.

We report structural and electrical transport properties of a family of π-stacking soluble organic semiconductors, N,N‘-dialkyl-3,4,9,10-perylene tetracarboxylic diimides (alkyl − pentyl [1], octyl [2], and dodecyl [3]). The structures of evaporated polycrystalline films of 1−3 were studied using X-ray diffraction and atomic force microscopy. Films of 1−3 pack similarly with the direction of π−π overlap in the substrate plane. Organic thin film transistors (OTFTs) based on 1−3 deposited on SiO2 gate dielectric showed linear regime electron mobilities of 0.1, 0.6, and 0.2 cm2/(V s), respectively, corrected for contact resistance. OTFTs of 2 had saturation electron mobilities as high as 1.7 cm2/(V s) with on-to-off current ratios of 107. Variable temperature measurements were used to examine the charge transport kinetics in the range 80−300 K and revealed (1) thermally activated electron mobilities with activation energies dependent on gate voltage and (2) the presence of well-defined isokinetic points, i.e., temperatures at which Arrhenius plots at different gate voltages intersect for a given film. Isokinetic points indicate a common charge transport mechanism and can be explained in terms of the multiple trapping and release (MTR) transport model. MTR assumes trap-limited band transport, and quantum chemical calculations were used to verify that delocalized transport is likely in 1−3; a conduction bandwidth of 0.58 eV was calculated for 1. Using MTR, the trap concentrations were estimated to be ∼1012 cm-2 for deep traps, and ∼6 × 1013 cm-2 for shallow traps. However, a nonmonotonic dependence of the electron mobility on gate voltage was also observed, which is not predicted by MTR and suggests that the transport mechanism is more complicated, perhaps due to the discrete layered structure of these materials. The high values for the electron mobility and on-to-off current ratio suggest that substituted perylene diimides represent a promising class of n-channel conductors for OTFTs.

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Thin‐film transistors (TFTs) based on a new n‐channel organic semiconductor (DCMT; see Figure) are reported. An electron mobility as high as 0.2 cm2/V s was observed, as well as ambipolar TFT behavior. Variable temperature measurements reveal that electron conduction is activated, with a small activation energy of 35 ± 10 meV. These results demonstrate that quinoidal oligothiophenes are a promising new class of organic semiconductors for TFTs.