Nickel complexation and photophysics of alkylanthracenyl dioxocyclam macrocycle derivatives

Ligands H2L in which (10-R-anthracen-9-yl) methyl moieties (R = H, Me, Et) are covalently joined (6-position) to the 5,7-dioxocyclam macrocycle framework have been prepared and their nickel( II) complexes isolated and characterized. X-Ray crystal structures of (NiL)-L-II (R = H, Me) complexes show that in both structures the anthracene moieties are folded around towards the mean plane of the macrocycles; dihedral angles between the mean anthracene and macrocyclic planes of c. 22 degrees are subtended. H-1 n.m.r. spectrometry indicates that the folded conformations are retained in solution. Absorption and fluorescence spectra, fluorescence quantum yields and lifetimes of the anthracenyl macrocycles are reported. Absorption spectra of the metal complexes are red-shifted and the fluorescence is dramatically quenched compared to the metal-free compounds indicating a strong electronic interaction between the anthracene and the complexed dioxocyclam macrocycle.