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

Abstract

A dense high-mobility organic semiconductor presents anomalously high negative and positive uniaxial thermal expansion across an isosymmetric phase transition.

Structural Odd–Even Effect Impacting the Dimensionality of Transport in BTBT‐CnOH Organic Field Effect Transistors

“…Whereas this study focusses on the inter and intramolecular packing mode which is mostly independent of temperature when there are no phase transitions, intermolecular interactions may be more or less dependent on temperature. This has been previously demonstrated by us for n=4,5,6 [15,17,33] and will be the topic of a forthcoming study. Notes: Cell lengths in Å; cell angles in °, cell volume in Å 3 .…”

“…The single-crystal structure of BTBT-C6OH was already reported before by us [16,17] and by comparison with the structure of BTBT-C8 it could be inferred that in BTBT-C6OH, BTBT half of the cores are rotated by 180° around their long axis in an inverted herringbone organization with only one type of S⋯S contact, namely, edge-to-edge S⋯S contacts with S⋯S distance of 3.545 Å, whereas face-to-edge S⋯S contacts are absent in this case. As a result, the structure of BTBT-C6OH has a more 1D character than that of BTBT-C8.…”

“…Out-of-plane X-ray diffraction realized in Bragg-Brentano configuration on thin BTBT-CnOH films vacuum evaporated on silicon wafers reveal that all members are self-organized according to a lamellar structure developing perpendicular to the substrate with characteristic The single-crystal structure of BTBT-C6OH was already reported before by us [16,17] and by comparison with the structure of BTBT-C8 it could be inferred that in BTBT-C6OH, BTBT half of the cores are rotated by 180° around their long axis in an inverted herringbone organization with only one type of S⋯S contact, viz. edge-to-edge S⋯S contacts with S⋯S distance of 3.545 Å, whereas face-to-edge S⋯S contacts are absent in this case.…”

Thermal expansion properties of organic crystals: a CSD study

“…Subsets were defined consisting of only those values from compounds with at least three data collections at different temperatures in a temperature interval larger than 50 K and for which a fit assuming a linear dependency on temperature yielded a goodness of fit value R 2 of at least 0.75, 0.80, 0.85, and 0.90. As was outlined elsewhere 48 the dependency of the thermal expansion need not be linear, especially at temperatures well below the Debye temperature 52 or over continuous first-order (isosymmetric) phase transitions, 53,54 but in nearly all practical cases there is no need to go beyond a linear model. These high-quality subsets contain proportionally more studies than the complete set of compounds in which the same compound was measured in the same laboratory on the same diffractometer and should be qualitatively more homogeneous than the complete set.…”

On the crystal forms of NDI-C6: annealing and deposition procedures to access elusive polymorphs

“…Looking at the results obtained, we can immediately see that both polymorphs have a negative thermal expansion (NTE) along one principal axis, this behaviour is uncommon but it has been described in different materials before, for example in BHH-BTBT. 37,38 In Form a, the highest positive thermal expansion positive thermal expansion (PTE) of 308 MK À1 can be considered a huge expansion 39 and it affects the distances between the layers (see Fig. 10a), which involves mainly the alkyl chains, while the NTE occurs inside the layer and affects mainly the distances between the side-by-side aromatic core, these two effects promote the conversion into Form g, where the alkyl chains are more stretched, and the columns are closer.…”