Pendant antennae, lanthanide complexes

The Eu(III) and Tb(III) complexes of 36, developed by Parker et al., showed modulation of the lanthanide emission caused by changes in pH [139]. The coordinating antenna was covalently attached to the complex but only coordinates to the metal centre under specific pH conditions. This was demonstrated on a cyclen complex where three carboxylate pendant arms were attached, allowing coordination to take place, and resulted in the formation of a charge-neutral complex. The fourth position contained an aromatic sulfonamide tethered via an ethyl carbon chain, 36a-36c. Studies showed that luminescence was switched on when the complexes were in alkaline conditions because the two metal-bound waters (q = 2) were displaced. This led to a situation where the pendant aryl sulfonamide groups were coordinated... 

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