Switching of emission of a styryl dye in cucurbit[7]uril: A comprehensive experimental and theoretical study

• Styryl dye DASPMI forms 1:1 and 2:1 complexations with CB[7].
• Interaction of CB[7] with DASPMI causes structural change of dye.
• Release of DASPMI from CB[7] on addition of NaCl marked by colour change of the solution.
• Calculations corroborate the structural change of DASPMI inside CB[7].
• One carbon atom in the styryl part with positive charge gets too close to a carbon atom of CB[7].

Intriguing colour change and change in fluorescence band of 2-(4-(dimethylamino)styryl)-1-methylpyridinium iodide from nonpolar to polar protic solvent, and also from molecular container cucurbit[7]uril environment to polar protic solvent has been reported here. This interesting colour change of this dye with respect to the medium makes this dye useful as a sensor. Change in spectral characteristics of DASPMI along with change of colour from orange to yellow with increasing polarity of medium is interpreted as due to negative solvatochromatism. Complexations of probe–cucurbit[7]uril (1:1 and 2:1) cause structural change of the probe molecule due to hydrogen bond interaction of cationic part of the dye with CO group of cucurbit[7]uril and the colour change of the solution ensued. On addition of sodium chloride to the inclusion complex the dye is released from cucurbit[7]uril interior with colour of the solution reverted back. Theoretical results show that one carbon atom in the styryl part containing the positive charge gets too close to a carbon atom of cucurbit[7]uril to cause a phenomenal increase of dipole moment by 10X.

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