An unforeseen polymorph of coronene by the application of magnetic fields during crystal growth

Abstract

The continued development of novel drugs, proteins, and advanced materials strongly rely on our ability to self-assemble molecules in solids with the most suitable structure (polymorph) in order to exhibit desired functionalities. The search for new polymorphs remains a scientific challenge, that is at the core of crystal engineering and there has been a lack of effective solutions to this problem. Here we show that by crystallizing the polyaromatic hydrocarbon coronene in the presence of a magnetic field, a polymorph is formed in a β-herringbone structure instead of the ubiquitous γ-herringbone structure, with a decrease of 35° in the herringbone nearest neighbour angle. The β-herringbone polymorph is stable, preserves its structure under ambient conditions and as a result of the altered molecular packing of the crystals, exhibits significant changes to the optical and mechanical properties of the crystal.

Low temperature magneto-morphological characterisation of coronene and the resolution of previously observed unexplained phenomena

“…Secondly, regarding the optical response of coronene, our previous work has already established that the way in which each polymorph interacts with light differs significantly23. It would therefore be likely that this difference would have been observed in previous spectroscopic studies of coronene at low temperatures.…”

“…Without rigorous explanation of this anomalous behaviour, the use of coronene as a valid model for the physical properties of graphene and for all of the predicted properties gleaned from computational modelling cannot be justified. Our recent work23 has revealed a previously unknown enantiotropic polymorph of coronene (β-coronene) Fig. 1(b).…”

Freezing water at constant volume and under confinement

“…Other recent works have leveraged similarly unconventional thermodynamic boundary conditions to reveal previously inaccessible thermodynamic and kinetic information 32 , using freeenergy expressions that can include forms of thermodynamic work beyond temperature and pressure-including surface work (size, adsorption) 33,34 , elastic work (epitaxy, stress-strain) 35,36 , electromagnetic work (electrical polarization, magnetic polarization) 37,38 , chemical work (such as compositional variation, precursor activity) 39,40 , and more. These findings as a whole suggest that the Gibbs free energy alone is unable to capture the wide range of thermodynamic equilibria and kinetic behaviors encountered in materials systems in the diverse modern technological environment.…”

γ‐Herringbone Polymorph of 6,13‐Bis(trimethylsilylethynyl)pentacene: A Potential Material for Enhanced Hole Mobility

“…The existence of polymorphs leads to ambiguity in structural prediction, and hence, charge‐transfer properties. Therefore, it is essential to obtain a clear idea of the structure adopted by the molecules in each polymorph and the conditions under which each polymorph is formed . Trialkylsilylethynyl pentacene derivatives display diverse packing arrangements in the crystalline state, with varying π‐orbital overlap .…”

“…[19] The existenceo fp olymorphs leads to ambiguity in structuralp rediction, and hence, chargetransfer properties.T herefore, it is essential to obtain ac lear idea of the structure adopted by the molecules in each polymorpha nd the conditions under which each polymorph is formed. [20][21][22][23] Trialkylsilylethynyl pentacene derivatives display diverse packing arrangements in the crystalline state, with varying p-orbital overlap. [24] The most commonly observed amongt hese arrangements is the slip-stacked packing, which is exemplifiedb yt he reported structure (1)o f6,13-bis(trimethylsilylethynyl)pentacene (TMS-pentacene).…”