Experimental and theoretical evidence of a supercritical-like transition in an organic semiconductor presenting colossal uniaxial negative thermal expansion

Chemical Science
Arie van der LeeJean-Sébastien Filhol

Abstract

Thermal expansion coefficients of most materials are usually small, typically up to 50 parts per million per kelvin, and positive, i.e. materials expand when heated. Some materials show an atypical shrinking behavior in one or more crystallographic directions when heated. Here we show that a high mobility thiophene-based organic semiconductor, BHH-BTBT, has an exceptionally large negative expansion between 95 and 295 K (-216 < α2 = α b < -333 MK-1), being compensated by an even larger positive expansion in the perpendicular direction (287 < α1 < 634 MK-1). It is shown that these anomalous expansivities are completely absent in C8-BTBT, a much studied organic semiconductor with a closely related molecular formula and 3D crystallographic structure. Complete theoretical characterization of BHH-BTBT using ab initio molecular dynamics shows that below ∼200 K two different α and β domains exist of which one is dominant but which dynamically exchange around and above 210 K. A supercritical-like transition from an α dominated phase to a β dominated phase is observed using DSC measurements, UV-VIS spectroscopy, and X-ray diffraction. The origin of the extreme negative and positive thermal expansion is related to steric hindrance betwee...Continue Reading

References

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Dec 1, 2017·Chemical Society Reviews·Chengliang WangWenping Hu

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Citations

Aug 25, 2020·Acta Crystallographica Section B, Structural Science, Crystal Engineering and Materials·Dan G DumitrescuArie van der Lee
Jun 8, 2021·Acta Crystallographica Section B, Structural Science, Crystal Engineering and Materials·Andrew D Bond
Jul 6, 2021·Chemical Science·Arie van der Lee, Dan G Dumitrescu
Oct 28, 2019·ACS Applied Materials & Interfaces·Victor M Fernandez-Alvarez, Michael H Eikerling

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Methods Mentioned

BETA
optical microscopy
X-ray

Software Mentioned

IMACET

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