Aggregate of Alkoxy-Bridged Re(I)-Rectangles as a Probe for Photoluminescence Quenching

Alkoxy-bridged rhenium(I) rectangles [{(CO)3Re(μ-OR)2Re(CO)3}2(μ-bpy)2] (1, R = C4H9; 2, R = C8H17; 3,
R = C12H25; bpy = 4,4‘-bipyridine) comprising long alkyl chains form optically transparent aggregates and
exhibit luminescence enhancement in the presence of water. The aggregation of Re(I)-rectangle was followed
using a light-scattering technique. Presumably, the enhanced luminescence efficiency resulted from restriction
of torsional molecular motion in the aggregates. In addition, the rate of bimolecular quenching of Re(I)-aggregates in the triplet excited state by various electron donors (amines) and acceptors (quinones) was efficient.
These results indicate that the excited state of aggregated Re(I) surfactants with an electron acceptor and
donor facilitate the electron-transfer quenching process after they became preassociated inside the Re(I)-aggregated species. These synthesized compounds may be useful fluorescent materials in optoelectronic
applications.