A family of metallocyclodextrins: synthesis, absorption and luminescence characteristic studies based on host–guest recognition

<div><p>A family of metallocyclodextrins bearing one, two, three or six β-cyclodextrin binding sites on their ligands have been synthesised, and their structures were confirmed by <sup>1</sup>H NMR, <sup>13</sup>C NMR, MALDI-TOF MS, UV–vis spectroscopy and elemental analysis. Comparative investigation of the luminescent properties of these metallocyclodextrins found that 6CD-Ru showed the strongest fluorescence intensity. The fluorescence quantum yield results show that 6CD-Ru exhibits the highest emission efficiency, as we expected. To gain insight into the binding properties of the most promising metallocyclodextrin 6CD-Ru, two guest compounds 4-dimethylaminoazobenzene-4′-carboxylic acid (Dab) and methylene blue (MB) were used as analytes. 6CD-Ru exhibited remarkable emission quenching compared with the reference compound CD-Ru. Furthermore, calculated binding constants demonstrated that 6CD-Ru has enhanced binding capacity due to the presence of multiple β-cyclodextrin binding sites. These prominent characteristics of 6CD-Ru suggest that it may be used to detect the two guests Dab and MB, and their analogues, with greater sensitivity, and the relevant research with these metallocyclodextrins is in progress in our group.</p></div>