Self-assembly triangular and square rhenium(I) tricarbonyl complexes: A comprehensive study of their preparation, electrochemistry, photophysics, photochemistry, and host-guest properties

A series of self-assembly macrocyclic compounds featuring fac-Re(CO)(3)X (X = Cl or Br) as corners and linear bipyridyl bridging ligands have been pre pared and characterized. Depending on the lengths as well as the bonding an gles of the bridging ligands, the resulting geometries of these macrocyclic complexes are squares {[ClRe(CO)(3)(mu-DPB)](4) (3) and [ClRe(CO)(3)(mu-AZ P)](4) (4)}, triangles {[BrRe(CO)(3)(mu-BPDB)](3) (6) and [BrRe(CO)(3)(mu-B PDDB)](3) (7)}, or a dimeric species {[ClRe(CO)(3)(mu-BPET)](2) (5)}. A gen eral mechanism for the self-assembly processes involving soluble intermedia tes is proposed. The photophysical properties of these macrocyclic compound s are dominated by the characteristics of the lowest excited states which v ary from metal-to-ligand charge transfer (MLCT) to ligand-localized pi --> pi* or n --> pi* transitions for the different molecules. Square 3 and tria ngles 6 and 7 are luminescent in room-temperature solution while square 4 a nd dimer 5 are nonemissive. An energy transfer mechanism from the MLCT exci ted state to the lowest nonemissive n --> pi* excited state is attributed t o the lack of emission in square 4. The emission from square 3 is assigned to (MLCT)-M-3 character. In the cases of triangles 6 and 7, emissions from the (1)pi - pi* state were observed, as evidenced by their short lifetimes and structured emission bands. The large strain imposed on the triangular s tructures of 6 and 7 results in these molecules being photoactive. Photolys is of 6 or 7 at 313 nm is observed to break the triangular structure to for m a polymeric structure. Square 4 exhibits reversible multielectron redox p roperties. Square 3 is also demonstrated to be a very effective host for ni tro-substituted aromatic compounds.