A Triad Fluorenone Derivative Bearing Two Imidazole Groups That Switches between Three States by Base and Acid Stimuli

2,7-Bis(2-phenyl-1H-imidazol-4-yl)fluorenone (BPIFO) was synthesized as a new fluorenone derivative bearing two imidazole moieties, and it exhibited remarkable and reversible changes in photo physi...