Synthesis and characterisation of highly emissive and kinetically stable lanthanide complexes suitable for usage ‘in cellulo’

The synthesis and photophysical characterisation are reported of a series of cationic, neutral and anionic europium and terbium complexes based on structurally related, nonadentate ligands based on the cyclen macrocycle. Each complex incorporates a tetraazatriphenylene moiety and overall absolute emission quantum yields are in the range 15–40% in aerated aqueous media. Dynamic quenching of the lanthanide excited state occurs with electron-rich donors, e.g. iodide, ascorbate and urate, and a mechanistic interpretation is put forward involving an electron transfer process. The cationic lanthanide complexes are taken up by NlH/3T3 cells and tend to localise inside the cell nucleus.