INTRAMOLECULAR EXCHANGE ENERGY-TRANSFER IN A BRIDGED BIMETALLIC TRANSITION-METAL COMPLEX - CALCULATION OF RATE CONSTANTS USING EMISSION SPECTRAL FITTING PARAMETERS

The photophysical behavior of the transition metal complexes {[bpy)(2) Ru](2)(bphb)}(PF6)(4), {[(tpy)(CN)Ru](2)-(bphb)}(PF6)(2), and [(bpy)(2 )Ru(bphb)Ru(tpy)(CN)(PF6)(4) (bpy = 2,2'-bipyridine, tpy = 2,2',6',2 ' '-terpyridine, bphb 1,4-bis(2,2'-bipyrid-4-yl)benzene) was investigate d in acetonitrile solution and low-temperature glasses. Luminescence s pectra, excitation spectra, and transient absorption decays of the thr ee complexes serve to show that intramolecular electronic energy trans fer from the MLCT excited state of the [(bpy)(2)Ru(bphb) chromophore t o the MLCT state of the tpy-containing chromophore occurs in the unsym metric bimetallic complex. Nearly complete energy transfer from the [( bpy)(2)Ru(bphb)] chromophore to the tpy-containing chromophore was obs erved even in 4:1 ethanol:methanol glasses at 20 K. A semiclassical ex change energy transfer mechanism was used to treat the available data; the Franck-Condon weighted density of states (FCWD) was obtained usin g parameters determined from fits of luminescence spectra. Given the F CWD at room temperature and the experimental rate constant, an electro nic coupling matrix element of approximately 60 cm(-1) was determined for this system.