Luminescent Squares and Rings Based on Metal-to-Ligand Charge Transfer Excited States

Two types of luminescent cyclic metallomacrocycles containing Re(I)−2,2‘-bpy MLCT chromophores and diphosphine bridges (P-P) have been prepared by self-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 alternating Re(CO)2(P-P)2(bpy) and Re(CO)3(P-P)2Cl units. Complete structural assignment of the former, but not the latter, was accomplished using IR and NMR spectroscopies as well as by mass spectrometry.