Triple fluorescence of acridinedione: Locally excited, photoinduced electron transfer promoted charge transfer and anion induced charge transfer states

A dual emitting acridinedione fluorophore, 9-(4-(dimethylamino)phenyl)-3,4,6,7,9,10-hexahydroacridine-1,8(2H,5H)-dione (DMAADR-1), was synthesized and its dual fluorescence behavior was found to be greatly affected by the presence of both transition metal ions and anions. Addition of transition metal ions results in the fluorescence enhancement in the locally excited (LE) state with the disappearance of charge transfer (CT) state by suppression of photoinduced electron transfer (PET) process. Whereas in the case of anions like acetate, phosphate and fluoride, a triple fluorescence is observed, corresponding to the LE state, PET promoted CT state and anion induced CT (AICT) state. Since the present molecule can act as heteroditopic host for both transition metal ions and anions, we have carried out simultaneous binding studies of metal ions and anions. These studies clearly proved the sequestering of the ions and thus tuned the fluorescence of DMAADR-1 between OFF–ON states.