Rigidly Tethered Bis-phosphoric Acids: Generation of Tunable Chiral Fluorescent Frameworks and Unexpected Selectivity for the Detection of Ferric Ions

We describe the straightforward synthesis of a series of bis-phosphoric acids (R,R)-1a-d, featuring two chiral 1,1-binaphthyl-phosphoric acid units that are tethered by rigid, -conjugated linkers. The nature of the linker has a profound influence on the properties of the bis-phosphoric acids, such as their self-association behavior and their interaction with metal ions. This led to the identification of one preferred bis-phosphoric acid (R,R)-1d, which shows selective fluorescence quenching in the presence of ferric ions (Fe3+). Thus, (R,R)-1d could be applied for the detection of Fe3+, even in the presence of a variety of other metal ions. The chiral nature of the bis-phosphoric acid enables the interaction with Fe3+ to be followed by CD spectroscopy, providing a complementary detection mode with the same probe.