Having demonstrated the robust and reversible photoisomerization of ligand 1 under conditions relevant to G4 DNA folding, we turned our attention to a proof-of-concept experiment that would provide an initial indication of its suitability as a photoresponsive G4 ligand. In order to benchmark the new ligand against our previously reported photoresponsive derivatives, we initially studied the binding to the human telomeric G4 sequence in potassium buffer (telo23-K + ). UV/Visible titrations studies revealed an association constant (Ka) of 2.07