Polymorphism in pentacene

Abstract

Pentacene, C(22)H(14), crystallizes in different morphologies characterized by their d(001)-spacings of 14.1, 14.5, 15.0 and 15.4 A. We have studied the crystal structure of the 14.1 and 14.5 A d-spacing morphologies grown by vapour transport and from solution. We find a close correspondence between the 14.1 A structure reported by Holmes, Kumaraswamy, Matzeger & Vollhardt [Chem. Eur. J. (1999), 5, 3399-3412] and the 14.5 A structure reported by Campbell, Monteath Robertson & Trotter [Acta Cryst. (1961), 14, 705-711]. Single crystals commonly adopt the 14.1 A d-spacing morphology with an inversion centre on both molecules in the unit cell. Thin films grown on SiO(2) substrates above 350 K preferentially adopt the 14.5 A d-spacing morphology, with a slightly smaller unit-cell volume.

Anisotropy of the mobility of pentacene from frustration

“…1, has been reported by several groups. [8][9][10] It is a layered structure, triclinic, with spacegroup P1. The molecular layers consist of pentacene molecules arranged in a herringbone pattern.…”

“…9) with a 4×4×2 k-point mesh. 18 Convergence was tested with a 6×6×4 mesh and found to be sufficient.…”

“…We chose the unit vectors following Ref. 9, with a and b in the molecular plane and c inter-relating the molecular planes. The unit cell contains two inequivalent molecules.…”

“…6 Despite the presence of at least four different polymorphs, 7 there are no structural phase transitions observed for the most stable polymorph, the single crystal polymorph. [8][9][10] The layered crystal structure indicates a highly two-dimensional charge transport.…”

A Polymorph Lost and Found: The High‐Temperature Crystal Structure of Pentacene

“…[5,6] However, this particular structure has not been reproduced in subsequent crystalgrowth experiments. Various structure determinations on single crystals grown in different ways have consistently revealed different triclinic structures [7][8][9] (e.g. polymorph).…”