Ground and excited state intramolecular proton transfer controlled intramolecular charge separation and recombination: A new type of charge and proton transfer reaction

A novel β-diketone 1-(4-(9-carbazol)phenyl)-3-phenyl-1,3-propanedione (CDBM) has been synthesized. When excited at 380 nm, this molecule shows single fluorescence. However, when excited at 338 nm, it shows dual fluorescence. A Al3+ complex Al(CDBM)3 has been synthesized to investigate the dual fluorescence of CDBM. It is found that this complex shows single fluorescence under all excitation. This result indicated that the dual fluorescence of CDBM may relate to the intramolecular proton transfer reaction. Based on the experimental and theoretical studies of CDBM, N-(4-cyanophenyl)carbazole (CBN) and Al(CDBM)3, a “ground and excited state intramolecular proton transfer controlled intramolecular charge separation and recombination” mechanism is proposed to explain the unusual excitation-dependent dual fluorescence of CDBM.