Ligand luminescence and photoinduced charge separation in bis(naphthalene) substituted fourteen-membered tetraazamacrocyclic complexes of CuII and NiII

Abstract

Deaerated solutions of complexes of Ni^II and Cu^II of a bis(naphthalene) substituted fourteen-membered tetraazamacrocycle exhibited medium-dependent luminescence when they were irradiated at 351 or 337 nm. The addition of Cu(CH₃CN)₆²⁺ in increasing concentrations resulted in the formation of a ground state adduct and led to displacements of the emission spectrum toward shorter wavelengths and to a progressive quenching of the luminescence. The rate of the luminescence decay was also dependent on the medium and on the monitoring wavelength and was fitted by single or multiple exponentials with lifetimes shorter than 30 ns. Steady state irradiations of the complexes at 370 nm induced a minor conversion among tautomeric forms. Transient photochemical products with lifetimes of several hundred ns were observed via flash photolysis and assigned as metal–ligand radical species. A mechanism for the formation of such intermediates and various ground and excited state species is proposed.