Luminescent squares and rings based on metal-to-ligand charge transfer excited states

Two types of luminescent cyclic metallomacrocycles containing Re(I)-2,2'-bp y MLCT chromophores and diphosphine bridges (P-P) have been prepared by sel f-assembly. The "petite squares" are tetramers based on trans-cis-Re(CO)(2) (P-P)(2)(bpy) units, while the "grand rings" are octamers composed of alter nating Re(CO)(2)(P-P)(2)(bpy) and Re(CO)(3)(P-P)(2)Cl units. Complete struc tural assignment of the former, but not the latter, was accomplished using IR and NMR spectroscopies as well as by mass spectrometry.