SOLVENT DEPENDENT BEHAVIOR OF ENERGY-TRANSFER IN A MIXED-METAL RUTHENIUM(II) RHENIUM(I) COMPLEX/

The absorption and emission properties of (bpy)(2)Ru(bb)(2+), Ru(bpy)( 2)(bb)Re(CO)(3)py(3+) and (bb)Re(CO)(3)py(1+), where bpy is 2,2'-bipyr idine, bb is 1,2-bis(4-methyl-2,2'-bipyridyl-4'-yl)et and py is pyridi ne, were studied in various solvents. Absorptions attributed to d pi(R u)-->pi(1)(bpy) were located between 400 and 500 nm, those attributed to d pi(Ru)-->pi(2)(bpy) and d pi(Re)-->pi*(bb) were found between 3 00 and 400 nm, and those attributed to pi-->pi (intraligand) were obs erved between 200 and 300 nm. The absorption energy maxima of the d pi (Ru)-->pi(1)(bpy) transition followed the optical dielectric constant of the solvent defined by the (1-D-op)/(2D(op)+1) relationship. In th e heterometallic complex, absorption of light in the 300-400 nm region was partitioned between the ruthenium and rhenium centers. Emission i n solution at room temperature was observed from the ruthenium center upon excitation at either 436 or 355 nm. While emission was also obser ved from the rhenium center in (bb)Re(CO)(3)py(1+) when excited at 355 nm, none was observed from the rhenium site of the mixed metal comple x. The excitation energy absorbed by the rhenium center in this comple x was transferred to the ruthenium center with greater than 80% effici ency. The energy transfer process was rapid as noted by the transient absorption spectrum of the heterometallic complex, which contained onl y the features related to the bpy(-) radical and the Ru(II) bleach. In addition, an inverse (1-D-op)/(2D(op)+1) dependence on the emission e nergy maxima of (bb)Re(CO)(3)py(1+) was observed.