The effect of the linker size in C2-symmetrical chiral ligands on the self-assembly formation of luminescent triple-stranded di-metallic Eu(iii) helicates in solutionElectronic supplementary information (ESI) available. See DOI: 10.1039/c8dt02753f

Chiral lanthanide-based supramolecular structures have gained significant importance in view of their application in imaging, sensing and other functional purposes. We have designed chiral C 2 -symmetrical ligands ( L ) based on the use of two 2,6-pyridine-dicarboxylic-amide moieties ( pda ), that differ from one another by the nature of the diamine spacer groups (from 1,3-phenylenedimethanamine ( 1 ( S , S ), 2 ( R , R )) and benzene-1,3-diamine ( 3 ( S , S ), 4 ( R , R )) to much bulkier 4,4′-(cyclohexane-1,1-diyl)bis(2,6-dimethylaniline) ( 5 ( S , S ), 6 ( R , R ))) between these two pda units. The self-assembly between L and Eu( iii ) ions were investigated in CH 3 CN solution at low concentration whereby the changes in the absorbance, fluorescence and Eu( iii )-centred emission spectra allowed us to model the binding equilibria occurring in the solution to the presence of [ Eu:L 2 ], [ Eu 2 :L 2 ], [ Eu 2 :L 3 ] assemblies and reveal their high binding constant values. The self-assembly in solution were also studied at higher concentration by following the changes in the 1 H NMR spectra of the ligands upon Eu( iii ) addition, as well as by using MALDI-MS of the isolated solid state complexes. The chiroptical properties of the ligands were used in order to study the structural changes upon self-assembly between the ligands and Eu( iii ) ions using circular dichroism (CD) and circularly polarised luminescence (CPL) spectroscopies. The photophysical properties of [ Eu 2 :L 3 ] complexes were evaluated in solution and showed a decrease of luminescence quantum yield when going from the ligand with smaller ( 1 ( S , S )) to bulkier ( 5 ( S , S )) linker from ∼5.8% to ∼2.6%. While mass-spectrometry revealed the possible formation of trinucler assemblies such as [ Eu 3 :L 3 ] and [ Eu 3 :L 2 ]. The formation, stability constants and luminescence of chiral Eu( iii ) supramolecular assemblies were studied in CH 3 CN.