Pressure-Induced Conformational Change in Organic Semiconductors: Triggering a Reversible Phase Transition in Rubrene

A high-pressure polymorph of the
organic semiconductor rubrene
was obtained above 6.0 GPa by hydrostatic compression of the triclinic
form. In the high-pressure phase, rubrene adopts an unexpected and
previously unobserved conformation, which is ca. 70 kJ/mol less stable
than the planar one observed in the ambient-pressure phase and is
characterized by a unique “double twisting” of the tetracene
core and “scissoring” of the lateral phenyl groups,
which favor the formation of C–H···π contacts.
The evolution of the structure as a function of pressure is monitored
and quantified by Hirshfeld surfaces analysis and calculations of
lattice and intermolecular interaction energies. The isosymmetric
single-crystal-to-single-crystal transition is fully reversible and
is primarily driven by a reduction in molecular volume.