Convenient synthesis of multivalent zinc(II)–dipicolylamine complexes for molecular recognition

A pair of novel dipicolylamine ligands bearing isothiocyanate groups were used as conjugation reagents to prepare multivalent molecules with anionic recognition capability. The isothiocyanates were reacted with two classes of dendritic scaffolds bearing primary amines, squaraine rotaxanes, and PAMAM dendrimers, and the products were converted into water soluble zinc(II) coordination complexes. The multivalent squaraine rotaxanes exhibit high fluorescence quantum yields in water and are very well suited for biological imaging applications.