DPA-substituted coumarins as chemosensors for zinc(<scp>ii</scp>): modulation of the chemosensory characteristics by variation of the position of the chelate on the coumarin

The sensory capabilities of two novel di(2-picolyl)amine (DPA)-substituted coumarins are described and it is shown that the variation of the point of attachment of the DPA group to the coumarin framework controls their sensing behavior: the 4-substituted system is a CHEF-type sensor that shows a significant increase in fluorescence intensity upon Zn(2+) binding, whereas the 3-substituted system is a ratiometric sensor.