A new blue light-emitting terphenyl-bridged bisbenzimidazolium salts: Synthesis, crystal structure, and photophysical properties

Eight novel terphenyl-bridged bisbenzimidazolium salts bearing N-alkyl side chains were synthesized by alkylation and quaternization of terphenyl-bridged bisbenzimidazoles with excess alkyl bromides, using sodium carbonate as the base in N,N-dimethylformamide solution. The bisbenzimidazolium salts showed good solubility in water and common organic solvents, such as dichloromethane, chloroform, methanol, acetonitrile, and N,N  -dimethylformamide. They emitted violet–blue light (λmaxEm≈397–400nm) with fluorescence quantum yields of 0.65–0.78 in aqueous solution, whereas they emitted blue light (λmaxEm≈420–441nm) in thin films. The photoluminescent properties and crystal structure of the bisbenzimidazolium salts have been investigated.

► A series of novel terphenyl-bridged bisbenzimidazolium salts bearing N-alkyl side chains were synthesized.
► The compounds emit violet–blue light with high quantum yields in solution.
► The compounds offer good solubility in water and a range of organic solvents.