In this paper, we present a new effect influencing the operation of organic field‐effect transistors resulting from the choice of gate insulator material. In a series of studies it was found that the interaction between the insulator and the semiconductor materials plays an important role in carrier transport. The insulator is not only capable of affecting the morphology of the semiconductor layer, but can also change the density of states by local polarization effects. Carrier localization is enhanced by insulators with large permittivities, due to the random dipole field present at the interface. We have investigated this effect on a number of disordered organic semiconductor materials, and show here that significant benefits are achievable by the use of low‐k dielectrics as opposed to the existing trend of increasing the permittivity for low operational voltage. We also discuss fundamental differences in the case of field‐effect transistors with band‐like semiconductors.

Three synthetic protocols have been employed to prepare solution-processable poly (4,4dialkylcyclopentadithiophenes). These polymers are fused-ring analogues of poly(3-alkylthiophenes) and structural analogues of the polyfluorenes. Oxidative polymerization of 4,4-dialkylcyclopenta[2,1-b;3,4-b′]dithiophenes using iron (III) chloride gave high-molecular-weight polymers, whereas nickel-catalyzed polymerization of the 2,6-dibromo derivatives via in situ-generated thienylmagnesium and thienylzinc reagents gave moderate-molecular-weight polymers. The structures of the polymers were confirmed by NMR spectroscopy and MALDI-TOF mass spectrometry. In the polymerization using organomagnesium intermediates, some chain capping by methyl end groups was observed. This side reaction can be avoided by polymerization of the organozinc reagents. Post-functionalization of the halogen termini of these polymers can be readily achieved using a cross-coupling with an aryl Grignard reagent. The main chain conjugation in these polymers can be directly correlated to the length of the polymer backbone because the UV-vis spectra of fractionated samples show absorption maxima that increase with the average degree of polymerization as determined by GPC, up to a limiting value of ∼20. UV-vis spectroscopy suggests that poly(4,4-dialkylcyclopentadithiophenes) do not self-assemble in the solid state, as has been previously observed for regioregular poly-3-alkylthiophenes.

In this work we present some experimental evidence of the existence of carbonyl-p electron cloud interactions. Such interactions are analogous to anion-p interactions, which have been predicted to be energetically favourable in the case of electron deficient aromatic rings. UV-Visible spectroscopy and cyclic voltammetry results obtained for 9,10-anthraquinone, 1,1 0 -bis-9,10anthraquinone, poly(9,10-anthraquinone-1,4-diyl) and other 1,4-diaryl substituted anthraquinone derivatives are described. It was found that the steric hindrance occurring between the carbonyl groups and the adjacent aromatic substituent forces the plane of the anthraquinone moiety and that of the aromatic substituent to adopt a nearly orthogonal conformation, resulting in relatively strong carbonyl-p interactions that affect both the UV-Vis absorption spectrum and the reduction potential of the compound. Moreover, in the case of thiophene substituted derivatives, the torsion angle between the anthraquinone moiety and its aromatic substituent is smaller and therefore carbonyl-p interaction effects are not observed in these compounds.

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