Oligothiophenes solid state properties

Well-defined oligothiophenes surrounded by bicyclo[2.2.2]octane fiameworks 173-176 have been synthesized and their crystal structures, electrochemical, optical properties have been studied. The solid state properties of the oligomers as a function of increasing number of thiophene units have been reported <03JOC8305>. 

The main interest of unsubstituted oligothiophenes lies in their solid-state properties and in their application as organic semiconductors in electronic devices. Oligothiophenes may be synthesized via two dilferent routes, either by C—C-linkage reactions between thiophenes and/or oligothiophenes or by ring closure reactions from acychc precursor molecules. 

The absorption maxima of the oligothiophene dimers in solution range from 361 nm (BT3) and 426 nm (BT5) to 451 run (BT7). These values are similar to the optical properties of the corresponding unsubstituted linear oligothiophenes T3-T6 [28]. There is only a minor redshift of max of ca. 9 nm in BT3 compared to T3 and BT5 compared to T5, which is probably due to a weak intramolecular electronic interaction of the arms in BT3 and BT5. Comparison of the solution and solid state spectra (Figure 6.2a, b) shows a distinct red shift of the films spectra, which is more pronounced for the more extended dimers... 

Drawn polythiophene films show enhanced conductivity along the drawn direction of the film [50,51,80]. This means that one-dimensional carrier transport along the polymer chain will be the prevailing electronic process. This feature should be probed by anisotropic (or dichroic) spectroscopic measurements. Meanwhile, the spectral profiles of the oligothiophenes taken in the solid state differ significantly from those in dilute solution (see Section 2.3). This implies that the electronic processes in the solid state are considerably different in the nature from those in solution. In this section we describe the spectroscopic characteristics of the polythiophenes and oligothiophenes in both the neutral and doped forms in the solid state and correlate these characteristics with electronic structure and properties. 

With respect to their properties in solution and the solid state, the model character and their applications as new materials, the end-capped oligothiophenes ECnT seem to be one of the best investigated series up to now. Due to their defined character, their elfective purification methods and controllable processability by vacuum evaporation highly pure materials are obtained. 

Structure and Properties of Oligothiophenes in the Solid State Single Crystals and Thin Films... 

The aim of this chapter is to review the structure and properties of solid state oligothiophenes, particularly single crystals and vacuum-deposited thin films. Particular attention is given to the influence of chain length and substitution keeping in mind their potential applications in electronic devices. 

One essential parameter for charge transport properties in solid state oligothiophenes is the distance between molecules. In the a-3T crystal, the shortest S- -S distances measured by Van Bolhuis et al. are those between the outer sulfur atoms of adjacent identical molecules, i.e. 3.690 A and 3.711 A respectively [51]. All other S- -S distances are 4.1 A or longer. 

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