Synthesis of Di- and Trixanthones that Display High Stability and a Visual Fluorescence Response to Strong Acid.

Three dixanthones ( 1- 3) and an unprecedented C_3h-symmetric trixanthone ( 4) were synthesized through a three-step approach in overall yields above 63 %. These compounds possessed a planar π-conjugated system and formed tight face-to-face columnar stacks, as confirmed by single-crystal structural analysis. In comparison with xanthone, the fluorescence emissions of compounds 1- 4 showed significant red-shifts, with improved quantum yields. Moreover, the fluorescence emissions of compounds 1- 4 could be modulated in a strongly acidic environment without decomposition, which led to a further red-shift of the emissions, as well as enhancement of the emission intensities. These compounds have potential applications as optoelectronic materials and/or chemosensors. [ABSTRACT FROM AUTHOR]