Rhenium diimine complex ligand

As the lowest excited state of many Re(I) diimine complexes is the emissive MLCT state, it can be tuned by chemical modification of the diimine ligand and the identity of the monodentate ligands. Figure 3 shows the UVA is absorption and emission spectra of a typical rhenium(I) diimine complex, /ac-Re(bpy) (COaCl (bpy = 2,2 -bipyridine) (la), measured in CH3CN. 

It has been also reported that Re—R bond homolysis can be promoted by the photoexcitation of mononuclear rhenium(I) complexes with a Re—alkyl bond, /ac-[Re(CO)3(a-diimine)R] (R = alkyl ligand). This type of the reaction also proceeds via a state, which is produced by the relaxation from the MLCT excited state. In the cases of R = ethyl (Et) and benzyl (Bz), the homolysis reaction proceeds efficiently. However, the reaction efficiency is much lower in the case R = methyl (Me) because the transition from MLCT to requires extra energy (Scheme 1). Using transient absorption spectroscopy, the state was... 

Another important type of LLCT state arising in diimine rhenium(I) tricarbonyl complexes is found in IRe (CO)3(diimine) complexes. When I replaces Cl or Br, the lowest excited states changes from being MLCT in nature to that of XLCT (halide-to-ligand charge transfer) in character. Figure 2 clearly shows that the lowest energy band of the transient absorption... 

Z)-Stilbene]Cr(CO)3 showed three optically accessible excited states. One of these excited states caused (E)-(Z) isomerization and the other resulted in a slow release of carbon monooxide. " Tetranuclear rhenium(I) tricarbonyl diimine complexes (20) with a stilbene-like bridging ligand showed efficient photoswitching properties. The accurate quantum yields of the photoisomerization of the mononuclear rhenium(I) tricarbonyl diimine complex could be determined readily by the H NMR technique in eombination with absorption spectroscopy. ... 

Villaume S, Daniel C (2005) Emission spectroscopy of metal-to-ligand-charge-transfer states of HRe(CO)3(H-DAB), model system for alpha-diimine rhenium tricarbonyl complexes. Comptes Rendus Chimie 8 1453-1460... 

New rhenium(I) biotin complexes containing the extended planar diimine ligands dppz and dppn (17) have been prepared to explore bifunctional biological probes [44], These complexes bind to double-stranded calf thymus DNA by intercalation, as revealed by absorption and emission titrations. HABA assays show that all the complexes bind to avidin with a stoichiometry of 4 1 ([Re] [avidin]). Similar to other rhenium(I) diimine biotin complexes described above, the emission intensities... 

When more conjugated diimine or pyridine ligands are used, the excited states of rhenium(I) carbonyl complexes can have substantial IL character. While the MLCT emission is often broad, with a lifetime in the submicrosecond to microsecond timescale, the IL emission usually has noticeable structural features, even in fluid solutions at ambient temperature. The emission lifetime is usually very long. A simple and widely applicable approach is to evaluate the ratio of the emission quantum yield and the emission lifetime (the product of the intersystem crossing efficiency and radiative decay-rate constant). Experimental values of... 

---