Effect of Substrate Surfaces for Crystal Growth of a Photochromic Diarylethene by Sublimation

The state of the substrate surface is one of the key factors in varying morphologies of crystals produced by the sublimation method of some organic compounds. In this work, we succeeded in separately preparing different morphologies of rodlike crystals of 1,2-bis(2,5-dimethyl-3-thienyl)perfluorocyclopentene (1a), which are classified into the hollow crystal and the feather-like crystal, by sublimation to glass substrates with the hydrophilic and hydrophobic surfaces, respectively. To clarify the crystal growth process on each surface of the glass substrate, we investigated miller indices of crystal faces attached to the substrate surface in the early stage of sublimation and crystal growth directions of these rodlike crystals from these crystal faces by X-ray diffraction measurements and polarizing microscopic observation. As a result, it was revealed that the heterojunction between the crystal faces produced in the early and following stages of sublimation leads to two different crystal morphologies. Moreover, it was confirmed that the heterojunctions occur in a specific orientation between these crystal faces because the lattice points in these crystal faces are in good agreement. Finally, we have demonstrated photomechanical behaviors of the hollow and feather-like crystals.

Automated summary

The state of the substrate surface is a key factor in the morphological variations of crystals produced by the sublimation method. In this study, the crystal growth processes and directions were investigated on hydrophilic and hydrophobic glass substrates, revealing the heterojunctions between crystal faces in different stages of sublimation. The photomechanical behaviors of the resulting crystal morphologies were also demonstrated.