High-pressure structure and phase behaviour of a naphthyl end-capped oligothiophene

by Nico Giordano (FS-PETRA-D (FS-PET-D Fachgruppe P02.2))


Nico Giordano, Suchismita Guha, Beverly Stewart, Jakob Kjelstrup-Hansen, and Matti Knaapila

Understanding macromolecular self-organisation is essential in the physics and materials science of π-conjugated molecules such as the thiophene derivatives owing to their intriguing opto-electronic properties and applications as thin film organic semiconductor materials (OSM). Fundamental principles in how charge transportation and other properties depend on intermolecular separation and relative displacements between molecules have already been well established.¹ ' ² Packing modifications are typically achieved by the chemical addition of bulky end-caps but another, less conventional, route is by the application of an external force. Pressure provides a clean tool to modify molecular packing and alter the physical properties without chemical interference, as has been shown for other optically active π-conjugated molecules.³

Here we present high-pressure single-crystal structures and molecular packing energies of the OSM, 5,5′-bis(naphth-2-yl)-2,2′-bithiophene (NaT2) which undergoes a subtle isostructural phase transition at ca. 3.5 GPa. The phase transition is fully reversible and is characterised by the formation of new S···H intermolecular contacts and a change in the compression pathway. The crystal undergoes a yellow to red colour change on compression that is also fully reversible. Single crystal X-ray diffraction data were collected to 7.6 GPa on beamline P02.2 at PETRA III and are supported by optical and Raman spectroscopy measurements.

5,5′-bis(naphth-2-yl)-2,2′-bithiophene undergoes a colour change from yellow to red on compression that is fully reversible on decompression.


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