Spectroscopic Properties of tpy Ru tppz RhCl3 PF

The electronic absorption spectra of the Ru(II)-Rh(III) complexes display transitions characteristic for ruthenium polyazine complexes. The tppz and tpy 71- 71 absorptions appear in the UV region. The lowest energy absorption at 516 nm is due to the Ru(d7i)- tppz(7i ) MLCT transition (Table 2). This MLCT transition is blue shifted with respect to the corresponding absorption of the homobimetallic system [(tpy)Ru(tppz)Ru(tppz)](PF6)4, which occurs at 548 nm. This blue shift is attributed to the presence of the chlorides making the Rh(III) more electron rich. 

Emission spectroscopy was used to study the excited state dynamics of [(tpy)Ru(tppz)RhCl3](PF6)2. The Ru(d7i)- -tppz(7i ) MLCT state once optically populated is known to undergo intersystem crossing to populate the often emissive MLCT state. The Rh(da ) LUMO provides for facile intramolecular electron transfer to produce the Ru(djt) Rh(dCT ) MMCT state (Fig. 20). This electron transfer leads to a quenching of the emission normally observed from the Ru(d7i)- tppz(jt ) MLCT excited states. For example, [(tpy)Ru(tppz)RhCl3](PF6)2 displays a weak emission at RT in deoxy-genated acetonitrile solution from the Ru(djt) tppz(jt ) MLCT state, 

Energy-transfer quenching of the emissive MLCT excited state by the Rh(III) is unlikely in this system due to the lower energy of the MLCT excited state, which will shift it below the energy typically expected for the rhodium LF state. At 77 K, an intense structured emission is observed in an ethanol/methanol glassy solvent with a concomitant increase in the excited state lifetime (r = 330 ns) (Table 2). This excited state lifetime is comparable to the reported excited state lifetime of [(tpy)Ru(tppz)Ru(tppz)](PFe)4 at 77 K (t = 360 ns). Similar excited state lifetimes for [(tpy)Ru(tppz)RhCl3](PF6)2 and 

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