Single and multiple binding of β-cyclodextrin and polymeric β-cyclodextrins to luminescent ruthenium(II) α-diimine complexes

A comprehensive study of the binding interactions between ruthenium complexes with multiple binding sites and monomeric and polymeric beta-cyclodextrins is presented. A variety of different binding modes involving single and multiple binding arrangements are found. Binding is critically dependent on the geometry of the guest and host and hydrophobicity effects. There is an optimal spacing of the cyclodextrin units in order to exploit the geometry of the multiple attachment points of the guest. On CD binding, the complexes are shielded from oxygen quenching. Quenching can be reduced by from 3 to greater than 10 times compared to the free complex even though only a small portion of the surface of the complex is protected. The greatly enhanced shielding, can be attributed to the excitation being localized in the protected region. With the polymeric hosts, the associated linker can also assist in shielding. Implications of these results to polymer supported quenchometric oxygen sensors are discussed.