A Spiropyran‐Based Ensemble for Visual Recognition and Quantification of Cysteine and Homocysteine at Physiological Levels

Isomerization of the ligand, followed by cooperative metal–ligand interactions leads to the ternary ensemble shown on the right, which has potential for the recognition and quantification of cysteine and homocysteine. The free ligand (left) is red-violet in solution, but when metal ions and cysteine or homocysteine are simultaneously introduced, the solution turns yellow.