Four organic dyes containing isophorone as the π-bridge unit were synthesised and their photophysical and electrochemical properties were characterised.

The title racemic spiro compound, C 26 H 14 Br 2 O, crystallizes with two independent molecules (A and B) in the asymmetric unit. The mean plane of the phenanthrene unit is twisted with respect to the mean plane of the fluorene unit by 82.38 (15) and 80.25 (5) in molecules A and B, respectively. In the crystal, the A and B molecules are linked by a pair of C-HÁ Á ÁO hydrogen bonds and a pair of short BrÁ Á ÁO contacts [2.935 (2) Å ], forming a centrosymmetric four-molecule unit. These units are linked by C-HÁ Á Á interactions, forming ribbons propagating along the b-axis direction. The ribbons are linked by CBrÁ Á Á interactions, forming layers parallel to the ab plane.

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