Abstract
Phase diagram of α-nT oligomers with n = 5–8 from the MD simulations.
Highlights
Despite that a-unsubstituted oligo-thiophenes (a-nTs) have been synthesized a long time ago and studied for many years, their phase behavior is still not fully understood
We extend the simulations reported in ref. 35 for a-6T to three other members of the family of a-nTs characterized by n = 5, 7 and 8, our aim being to understand the dependence of phase behaviour and the type of liquid crystalline (LC) phases formed on the molecular length of the a-nT molecule
For each of the a-nT systems with n = 5–8 studied in this work, phase behaviour was examined by performing cooling Molecular Dynamics (MD) runs under isobaric conditions at progressively lower temperatures starting from their Iso phase at a high enough temperature
Summary
Despite that a-unsubstituted oligo-thiophenes (a-nTs) have been synthesized a long time ago and studied for many years, their phase behavior (which governs electronic performance, and their application in thin-film transistors) is still not fully understood. The odd–even effect is evident in the simulated crystalline phases of the studied a-nTs and in other properties such as the density and the tilt angle which are found to alternate between high and low values for even- and odd-numbered a-nTs, respectively. It is interpreted here in terms of intra-molecular configurational changes taking place at the phase transition points. Journal of Materials Chemistry C microscopy (POM) measurements and observed that the a-6T (a-sexithiophene) crystal forms a nematic (Nem) phase when heated above 585 K, but determination of the clearing point (or isotropization temperature) was not successful. The POM and DSC analysis of Ponomarenko and Kirchmeyer,[33] for example, has demonstrated that 4T, 5T and 6T with terminal alkyl-substituents display high temperature-ordered Sm phases, whose type, is not easy to identify
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