Controllable Intramolecular Motions That Generate Fluorescent Signals for a Metal Scorpionate Complex.

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. © 1998 WILEY-VCH Verlag GmbH, Weinheim, Fed. Rep. of Germany.