Tunable fluorescence emission in pyrene-(2,2'-bipyridine) dyads containing phenylene-ethynylene bridges.

A synthetic route is described for the preparation of a series of pyrene-containing pi-conjugated 2,2'-bipyridine (bpy) ligands. These compounds have been investigated by steady-state and time-resolved fluorescence spectroscopy. They display intense visible absorption and fluorescence emission properties that can be very efficiently modulated by the complexation of zinc(ii) metal ions to the bpy coordinating unit. The solvatochromism of the emission band of the zinc(ii) complexes, the fluorescence quantum yields, and lifetimes in THF have been determined. Zinc(ii)-induced formation of a charge transfer singlet excited states induces an increase in dipole moment of more than 20 D. Semiempirical theoretical calculations were performed and allowed to assess the electronic nature of ground and excited states of the free ligands and and that of the corresponding zinc(ii) complexes.