pH-responsive molecular assemblies of pyridylbutadiene derivative with cucurbit[7]uril

Abstract

The interaction between red-emitting pyridinium derivative [4-((1E,3E)-4-(4-(dimethylamino)phenyl)buta-1,3-dien-1-yl)-1-methylpyridin-1-ium] (DABP) and cucurbit[7]uril was investigated using optical absorption, steady-state and time-resolved fluorescence and anisotropy measurements. The changes in the UV/Vis absorption, fluorescence spectral characteristics and lifetime, with a change in pH, reveal efficient binding of CB7 to the dye molecule. The cucurbit[7]uril encapsulated DABP brings ∼1.5 units upward pKa shift. The formation of supramolecular assemblies with 1:1 and 2:1 host-guest stoichiometries with CB7 at different pH conditions have been verified from 1H NMR, isothermal titration calorimetric studies and geometry optimization calculations. CB7-dye complexation and the ensuing morphological changes were revealed by SEM, AFM and optical microscopy images. This pH-responsive supramolecular assemblies of red-emitting DABP dye can find potential applications in biological imaging, optical pH-sensor and the construction of building blocks for the supramolecular architectures.