Dual emission from 2-(4′-N,N-dimethylaminophenyl)pyridoimidazole–nanoparticle composite: Effect of β-cyclodextrin

• Nanoparticles induce dual emission in pyridoimidazole derivatives.
• Ternary complex with β-cyclodextrin enhances the dual emission.
• Nanoparticles interact through pyridyl nitrogen rather than dimethyl amino moiety.
• Pyridoimidazoles stabilize nanoparticles more than benzimidazole molecule.
• Presence and position of the pyridyl nitrogen play crucial role in the interaction.

The interactions of the silver nanoparticles with 2-(4′-N,N-dimethylaminophenyl)benzimidazole and its nitrogen substituted analogues, 2-(4′-N,N-dimethylaminophenyl)pyridoimidazoles are investigated by absorption, steady-state and time resolved fluorescence, field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM) techniques. The surface plasmon resonance band, the FESEM and the TEM images of the particles suggest that the fluorophores can stabilize the nanoparticles even in the absence of any other stabilizing agent. On the other hand, in the absence of fluorophores the nanoparticles are unstable and coagulate. In contrary to the earlier literature reports that interactions of nanoparticles with intramolecular charge transfer (ICT) or twisted intramolecular charge transfer (TICT) species quenches their fluorescence, to the best of our knowledge, the first ever formation of TICT state by interactions of nanoparticles with the fluorophores is observed. The formation of TICT state in 2-(4′-N,N-dimethylaminophenyl)pyridoimidazoles results in dual emission. The TICT emissions from the nanoparticle-fluorophore complexes are weak. But the emissions become prominent upon complexation with β-cyclodextrin.

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