New polymorph grown in strong magnetic field

Researchers from the University of Bristol, the University of Bath and the High Field Magnet Laboratory (HFML) at Radboud University have grown a new type of coronene crystal by application of a strong magnetic field. A magnetic field suppresses the growth of the usual crystal structure (polymorph), thereby allowing the new one to grow in preference. The ability to magnetically control polymorphism opens up the possibility of discovering new polymorphs in other crystal systems, such as organic solid-state lasers, field-effect transistors and pharmaceuticals. The results have been published on May 10, 2016 in Nature Communications.

The arrangement of molecules in an organic crystal can be achieved in a number of different ways. These variations, or polymorphs, can have a profound effect on the physical properties of the resultant crystal. The research team led by Dr Simon Hall of the University of Bristol has successfully controlled polymorphism in the polyaromatic hydrocarbon coronene, producing a crystal structure that had never before been observed. They achieved this by simply growing crystals in the presence of strong magnetic fields.

Highlight polymorph

Growing coronene crystals in a magnetic field leads to a new crystal structure (β-coronene, left), which has a remarkably different optical appearance relative to the usual crystal structure (γ-coronene, right).

The new polymorph, which they name β-coronene, exhibits substantially altered electronic and physical properties when compared to those of the usual γ-polymorph (see figure). The change in the optical behaviour of the crystal is of particular note, with the new polymorph being a panchromatic light absorbing material, potentially of interest to the solar cell and photovoltaic communities.

The application of magnetic fields to intentionally control polymorphism is entirely novel and opens up the possibility of discovering magnetically accessible polymorphs in other crystal systems such as organic solid-state lasers, field-effect transistors and most tantalizingly, pharmaceuticals.

Jason Potticary, Lui R. Terry, Christopher Bell, Alexandros N. Papanikolopoulos, Peter C. M. Christianen, Hans Engelkamp, Andrew M. Collins, Claudio Fontanesi, Gabriele Kociok-Köhn, Simon Crampin, Enrico Da Como, Simon R. Hall
A new and unforeseen polymorph of coronene by the application of magnetic fields during growth; Nature Communications (2016); DOI: 10.1038/NCOMMS11555

Read the Bristol press release