Photochemical investigations of functionalised 1,4,7,10-tetraazacyclododecane ligands incorporating naphthyl chromophores

Abstract

The fluorescence properties of two macrocyclic ligands incorporating bis-(β-naphthyl amide) groups, –CH₂CON(CH₂C₁₀H₇)₂, as fluorophores, have been studied in water and acetonitrile. The ligands exhibit distinctive luminescence behaviour in the presence of quenching (e.g. Pb²⁺, Ni²⁺, Cu²⁺ and Eu³⁺) and non-quenching ions (e.g. Zn²⁺ and Cd²⁺). Excimer-to-monomer intensity ratios are affected to differing extents, as are the total integrated fluorescence intensities. The behaviour is contrasted to that reported previously for related ligands containing ‘isolated’ naphthyl units. The luminescence properties of the terbium complex of one of these earlier ligands, containing just one naphthalene group, have been studied in detail. Naphthyl-sensitised metal emission is observed but a nanosecond laser flash photolysis study reveals that back energy transfer to the naphthyl triplet state provides a facile deactivation mechanism for the metal excited state.