Solution of an elusive pigment crystal structure from a thin film: a combined X-ray diffraction and computational study†

Abstract

The previously unknown crystal structure of epindolidione has been determined from a thin film by combining diffraction data with calculations.

Abstract

Epindolidione, a hydrogen-bonded derivative of the organic semiconductor tetracene, is an organic pigment which has previously been used to produce stable OFETs with relatively high hole mobilities. Despite its use as an inkjet pigment and organic semiconductor, the crystal structure of epindolidione has proved elusive and is currently unknown. In this work, we report a crystal structure solution of epindolidione determined from vapor deposited thin films using a combined experimental and theoretical approach. The structure is found to be similar to one of the previously reported epindolidione derivatives and is most likely a surface-mediated polymorph, with a slightly different crystal packing compared to the bulk powder. The effect of substrate temperature on film morphology and structure is also investigated, where it is found that the crystallite orientation can be tuned by deposition at different substrate temperatures. The results also illustrate the possibilities for crystal structures to be solved from thin films.

Notes

†Electronic supplementary information (ESI) available: AFM micrographs of ∼7 nm thick samples; XRR data of ∼7 nm thick samples prepared at substrate temperatures of 200 and 350 K, including data fits and electron density profiles; chemical structure diagrams of the 2F-EPI and 2Cl-EPI derivatives; overlays of the thin film EPI structure with the halogenated derivative structures; graphical representation of the contributions of different intermolecular interactions to the Hirshfeld surfaces presented in Fig. 6. Crystallographic information file (cif) for the structure of EPI solved from a thin film, CCDC 1528520. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c7ce00227k