Large polarization of push–pull “Cruciforms” via coordination with lanthanide ions

Abstract

We report on two different series of conjugated push–pull compounds bearing dimethylamino donor and 1,3-dicarbonyl acceptor functionalities with a “bent” or“cruciform” shape, exhibit striking differences in their supramolecular recognition of lanthanide cations. Both series of compounds are effective to coordinate lanthanide cations (Sc³⁺ and Eu³⁺) in MeCN, CHCl₃ or MeOH solutions to the 1,3-dicarbonyl acceptor end. The stoichiometry of the complexes are largely dependent on the nature of the lanthanide cation, with Sc³⁺ forming preferentially 1 : 3 metal : ligand complexes, and Eu³⁺ forming 1 : 1 metal : ligand complexes. The coordination of the lanthanide cation results in an overall supramolecular polarization of the system and the redshifting of the intramolecular charge transfer band. The polarization of the “cruciform” systems is greatly enhanced with respect to the “bent” chromophores, reaching outstanding values for the red shift (238 nm, corresponding to an energy difference of 1.23 eV) with high binding constants (Log K_a >5.5).