Search

This article provides a brief account of the supramolecular chemistry of host–guest interactions and their binding mechanisms. The characterization of host–guest complexes, especially those based on cucurbituril (CB) macrocycles, by different methods such as absorption/fluorescence spectroscopy, 1 H NMR, mass spectrometry, and isothermal titration calorimetry has been described, especially with regard to determination of the stoichiometry and binding constants. Emphasis has been laid on the photophysics of CB-based supramolecular assemblies of fluorescent dyes that have technological and biological importance. The spectacular changes in their physicochemical properties such as solubility, stability, aggregation behavior, acidity constants, and cytotoxicity are also described. Effort has been made to give suitable examples of CB-encapsulated guest assemblies and to discuss their dynamic response toward external triggers such as light and metal ions. The potential applications of these host–guest systems to controlled uptake and release of drugs, construction of photo-functional devices, aqueous-based dye lasers, molecular architectures, etc., have been discussed.

Photophysical properties of 2,6-diamino-9,10-anthraquinone (2,6-DAAQ) dye have been investigated in different solvents and solvent mixtures. The fluorescence quantum yields, fluorescence lifetimes, radiative rate constants, nonradiative rate constants and absorption and fluorescence spectral characteristics show unusual deviations in the lower polarity aprotic solvents in comparison to those in other aprotic solvents of medium to higher polarities. The results indicate that the dye exists in different structural forms in the lower and in the medium to higher polarity solvents. Drawing an analogy with the results reported for other amino-substituted dyes, it is inferred that 2,6-DAAQ dye adopts a planar intramolecular charge transfer (ICT) structure in medium to higher polarity solvents, where the amino lone pairs are in good resonance with the anthraquinone pi-cloud. In the lower polarity solvents, however, the dye is inferred to exist in a nonplanar structure where the amino lone pairs are not in good resonance with the anthraquinone pi-cloud. Due to these structural differences, the dye displays significantly different photophysical behavior in the lower polarity solvents than in the other solvents of medium to higher polarities. Supportive evidence for the above structural changes has been obtained from ab initio quantum chemical calculations on the structures of the dye under different conditions. Unusual deviations in the photophysical properties of 2,6-DAAQ dye in protic solvents in comparison to those in aprotic solvents of similar polarities are attributed to the intermolecular hydrogen bonding effect involving the OH groups of the protic solvents and the quinonoid oxygens of the dye.

This short note presents a non-cyanide method for the detection of cadmium in the presence of copper.