Mono- and bis-N-functionalised cyclen with benzimidazolylmethyl pendant arms: Sensitive and selective fluorescent probes for zinc and copper ions

The Zn2+ and Cu2+ complexes of L1 and L2 ligands (L1: 1-(benzimidazol-2-ylmethyl)-1,4,7,10-tetraazacyclododecane, L2: 1,7-bis(benzimidazol-2-ylmethyl)-1,4,7,10-tetraazacyclododecane) were synthesised and characterised by means of NMR, EPR, and UV–Vis spectroscopies, X-ray determination and molecular modelisation (HF-DFT(B3LYP)/LANL2DZ). These studies showed that the 1:1 complexes were formed in which the benzimidazole arm(s) are coordinated to the metal ion. On addition of successive amounts of Zn2+ in CH3CN, the fluorescence emission of L1 increased linearly by a factor of 50 and the one of L2 by a factor of 5 while on addition of successive amounts of Cu2+ in CH3CN, the fluorescence emission of L2 decreased linearly to 80% of its initial value.