Metal-induced assembling/disassembling of naftalenediimide derivatives signalled by excimer emission

The new quadridentate bischelating ligands 2 and 3 display in solution the typical absorption and emission properties expected for naphthalenediimide derivatives. Spectrophotometric studies show that systems 2 and 3 interact with ZnII, CdII and CuI in CHCl3 or MeCN according to an apparent 1:1 stoichiometry. Molecular modelling, ESI-MS and 1HNMR experiments indicate that the complex pecies formed in the presence of stoichiometric amounts of metal ion are nonhelical [2+2] adducts. The metal-induced selfassembling process is signalled by an intense excimer-type emission caused by the intramolecular interaction of two naphthalenediimide subunits that face each other in the [2+2] adduct, as shown by molecular modelling studies. In the presence of excess metal ion, a disassembling process takes place, leading to a dinuclear complex with a 2:1 metal/ligand stoichiometry, in which the intramolecular excimer is no longer allowed to form because the interaction between the naphthalenediimide subunits has been lost. Thus, the verall metal-induced assembling/disassembling process is signalled by the appearance and disappearance of the excimer band in the emission spectrum.