F. Demanze

Structural, spectroscopic and device characteristics of octithiophene

Abstract As a step further in the design of efficient organic semiconductors, we report here on the structural, spectroscopic and device characterization of octithiophene (8T), the linear conjugated octamer of thiophene. The X-ray structure and optical spectra under polarized light of the 8T single crystal are described for the first time. Vapor deposited 8T behaves as a p-type semiconductor whose transport properties are investigated in thin film transistors (TFTs). In particular, we show that the use of high purity 8T enhances by two orders of magnitude its field-effect mobility in TFTs to reach μ FET = 1.8×10 −2 cm 2 /V.s, a value similar to that of non-substituted sexithiophene (6T).

Synthesis and electrical properties of cyano-substituted oligothiophenes towards n-type organic semiconductors

Abstract A series of α,ω-cyanooligothiophenes with three, four, five, six and seven β,β′-substituted terthiophenes have been synthesized using the palladium-catalyzed coupling reaction via organotin or organozinc intermediates. Schottky diode structures with metal/CN-6T-CN/metal using cyano end-capped sexithiophene and various metals were fabricated by vapour deposition. Electron injection and rectification ratio strongly depend on the metal contact which is compatible with the electron affinity materials.

Electrcal properties of cyano-substituted oligothiophenes towards N-type organic semiconductors

The synthesis of cyano end-capped sexithiophene is reported using the palladium-catalyzed coupling reaction via organotin intermediates. Schottky diode structures with metal/CN-6T-CN/metal using cyano end-capped sexithiophene and various metals were fabricated by vapour deposition. Electron injection and rectification ratio strongly depend on the metal contact which is compatible with the electron affinity materials.

Push-pull substituted polythiophene

Abstract A series of bithienyls substituted in their 3,3′ positions by various electron-donating (OMe, hexyl) and electron-accepting (CN) groups has been synthesized. The electropolymerization is largely determined by the electronic effects of both substituents. We will first describe the electronic requirements for the electropolymerization to take place, and use the obtained data for the realization of a conjugated polythiophene bearing alternately electron donor and acceptor groups. The electro-optical properties of these polythiophenes show that the presence of electron-donating and electron-accepting groups leads to the formation of stable and highly localized polarons, resulting from the existence of multiple potential wells along the conjugated backbone.

Electrochemical oxidative coupling of cyano-substituted oligothiophenes

Conjugated bi- and terthiophenes have been substituted by cyano groups on several positions of the oligothiophene backbone. Their ability to form, after oxidation, longer oligothiophenes has been analyzed by electropolymerization. Whereas cyano-substituted bithiophenes and dicyanoterthiophenes were found to be unable to give longer products, monocyanoterthiophenes could be dimerized, leading to disubstituted sexithiophene derivatives. The electrochemical and optical behavior of the three new electrosynthesized dicyanosexithiophenes were studied and compared with those of shorter substituted cyano-oligomers.

Design and electrosynthesis of push-pull substituted polythiophenes

A series of bithiophenes substituted with donor and acceptor groups has been synthesized. The relationship between the electrochemical behaviour of these bithiophenes and their ability to electropolymerize is analysed and discussed. The antagonistic electronic effect of both substituents can be controlled in order to allow stereoregular polymerization to take place. The obtained polymer shows unusual electrochemical and electrooptical properties, associated with the presence of strong accepting and donating groups alternating along the conjugated backbone.