Simply by changing the pH value, the side chain of complex 1 can be reversibly moved between two positions. Coordination to the metal center through the nitrogen atom of the side chain at moderate pH values is accompanied by a decrease in fluorescence intensity (from IF=100% to IF=60%). A further decrease is observed upon deprotonation of the bound water molecule at higher pH (IF≤2%). Therefore, 1 can be seen as a molecular three-position switch.
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Fabbrizzi et al. (1998) studied this question.