On the elusive, non-emissive yet reactive, upper excited states of [(4,4′-bpy)ReI(CO)3(dppz)]PF6 (dppz = dipyridil[3,2-a:2′3′-c]phenazine)

Gradual solvation of [(4,4′-bpy)ReI(CO)3(dppz)]+ (dppz = dipyridil[3,2-a:2′3′-c]phenazine) by water molecules causes a quenching of the emission in accordance with Perrin’s model of spheres. The calculated radius of the sphere, r = 2.6 ± 0.2 Ǻ, is therefore very close to the distance from the Re center to the oxygen atom of the CO ligands, i.e., l = 2.73 Ǻ. In addition, excited state reactions with TEA produce [(4,4′-bpy−)ReI(CO)3(dppz)] and [(4,4′-bpy)ReI(CO)3(dppz−)]. This experimental observation is inconsistent with the formation of the products in the lowest lying and emissive dppz-centered 3ππ* excited state. Jablonski schemes based on the participation of excited states other than the lowest 3ππ* excited state are proposed.

Graphical abstractGradual solvation of [(4,4′-bpy)ReI(CO)3(dppz)]+ (dppz = dipyridil[3,2-a:2′3′-c]phenazine) by water molecules causes a quenching of the emission in accordance with Perrin’s mechanism. Perrin’s sphere is superimposed with the structure of the complex in the figure. The redox quenching shows the participation of excited states other than the lowest dppz-centered ππ* excited state.Figure optionsDownload full-size imageDownload as PowerPoint slide