Polyamine linear chains bearing two identical terminal aromatic units. Evidence for a photo induced bending movement

Several chemosensors bearing a fluorescent unit at both ends of a linear po lyamine chain were synthesised. The protonation as well as the association constants with Cu2+ and Zn2+ were determined by potentiometry in 0.15 mol d m(-3) NaCl at 298.1 K. In the case of 1,16-bis(1-naphthylmethyl)-1,4,7,10, 13,16-hexaazadecane hexahydrochloride (L1), formation of an excimer emissio n in aqueous acidic solutions was observed. The system was characterized by steady state fluorescence emission and by time resolved fluorescence. In t he ground state the molecule is expected to adopt a more or less linear con formation, while in the excited state a bending movement of the chain must occur in order to allow the excimer emission. The system can be viewed as a n elementary machine driven by light.