The π-conjugated polymers and organic molecules have been much attractive to the applications for semi-conductors, cell and optical devices. It is better for high densely-packed materials to improve the conversion efficiency between the optical and electric energies, so that a single crystal or materials consisted of large quantity of crystalline domains are preferred. However, such materials are not flexible and easily broken, namely rigid and brittle. To overcome the trade-off relationship between flexibility and crystallinity for the organic materials, we focused on a face-to-face slip-stacking phenomenon that occurs in some kind of organic crystals: the slip stacking relates to an elastic property of a material. Anthracene is well known as a π-conjugated organic molecule, and to show the red-shift as compared to that of benzene for the ultraviolet-visible absorption spectra. The crystalline phase of the anthracene is also known to be the face-to-edge packing structure. This packing does not show the slip stacking; therefore, the anthracene does not show flexible property but is brittle. On the other hand, we found that two-halogens appended anthracenes, such as 9,10-, 1,5-, and 1,8-dibromo (or chloro) anthracenes, form the face-to-face or close packing structure from the X-ray diffraction; 2,6-dibromoanthracene crystal forms the face-to-edge packing structure. Especially, the 9,10-dibromoanthracene formed a fluorescent centimeter-scale needle-like single crystal and it showed an elastic property; like a flexible supramolecular three-dimensional polymer, while the 2,6-dibromoanthracene did not form the needle-like crystal and was brittle. In this study, we discuss mainly the molecular motion of the 9,10- and 2,6-dibromoanthracenes by means of solid-state13C NMR.

Solid-state 13C NMR and X-ray diffraction studies of dibromoanthracne crystals

ACS Fall 2020 Virtual Meeting

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