Synthesis, Structure, and Aggregation-Induced Emission of a Novel Lambda (Λ)-Shaped Pyridinium Salt Based on Tröger's Base

A novel Λ-shaped pyridinium salt 2,8-(6H,12H-5,11-methanodibenzo[b,f]diazocineylene)-di(p-ethenyl-N-methyl-pyridinium) ditosylate (abbreviated as DMDPS) based on Tröger's base was designed, synthesized and characterized. DMDPS exhibits a typical aggregation-induced emission (AIE) behavior that is virtually nonemissive in solution but highly luminescent in solid state. The difference between the structure and the optical properties of DMDPS and 1,4-phenyl-di(p-ethenyl-N-methyl-pyridinium) ditosylate (abbreviated as DPPS) are analyzed and compared. It is concluded that the loose stacking caused by twisted molecular configuration could reduce the distance-dependent intermolecular quenching effect to produce intense fluorescence in the aggregation state while the enantiomerization and/or the intramolecular vibrational motion which induce the nonradiative deactivation process could cause fluorescence quenching in the solution. As a water-soluble AIE-active material, DMDPS would have potential application in the area of optical and biological research.