Singlet Oxygen Responsive Molecular Receptor to Modulate Atropisomerism and Cation Binding.

In switchable molecular recognition, 1 O 2 stimulus responsive receptors offer a unique structural change that is rarely exploited. The employed [4+2] reaction between 1 O 2 and anthracene derivatives is quantitative, reversible and easily implemented. To evaluate the full potential of this new stimulus, a non-macrocyclic anthracene-based host was designed for the modular binding of cations. The structural investigation showed that 1 O 2 controlled the atropisomerism in an on/off fashion within the pair of hosts. The binding studies revealed higher association constants for the endoperoxide receptor compared to the parent anthracene, due to a more favoured preorganization of the recognition site. The fatigue of the 1 O 2 switchable hosts and their complexes was monitored over five cycles of cycloaddition/cycloreversion.