Synthesis and Photophysical Properties of Neutral Luminescent Rhenium-Based Molecular Rectangles

A series of neutral luminescent molecular rectangles [{Re(CO)3(μ-bpy)Br}{Re(CO)3(μ-L)Br}]2 (1−4) having fac-Re(CO)3Br as corners and 4,4‘-bipyridine (bpy) as the bridging ligand on one side and other bipyridyl ligands of
varying length (L) on the other side have been synthesized and characterized. The crystal structure of 1 shows a
rectangular cavity with the dimensions of 11.44 × 7.21 Å. When the cavity size is tuned from 1 to 4, a dimension
of 11.4 × 20.8 Å could be achieved, as revealed by the molecular modeling. These rectangles exhibit luminescence
in solution at room temperature. In particular, compound 4 containing 1,4-bis(4‘-pyridylethynyl)benzene (bpeb) as
bridging ligand shows the excited-state lifetime of 495 ns. Fine-tuning of the cavity size of the rectangles improves
their excited-state properties. These properties facilitate the study of excited-state electron-transfer reactions with
electron acceptors and donors and host−guest binding. Crystallographic information:  1·6CH3COCH3 is monoclinic,
P21/c, with a = 12.0890(2), b = 24.2982(2), and c = 12.8721(2) Å, β = 107.923(1)°, and Z = 2.