Photochemistry and Photophysics of Coordination Compounds

220 M.T. Indelli et al.
complex) can be evaluated by measuring the activation energy of the photosolvation
reaction originating from the MC state in low-temperature glycerol
matrices [39].
As it is obvious from the trend sketched in Fig. 1b, the cis-Rh(phen)2Cl2 +
complex has again a lowest MC excited state. It emits at ca. 710 nm [31] and, in
keeping with the typical ligand-field photoreactivity of d 6 metal complexes [7],
undergoes in fluid solution photosolvation of the chloride ligands [40–42].
This type of reactivity that has been exploited by Morrison and coworkers [43]
in an extensive series of studies on photoinduced binding to DNA and potential
applications of this class of complexes as photo-toxic agents.
Anumberofanaloguesofthecis-Rh(NN)2Cl2 + complexes, where the NN
represents various bidentate nitrogen donors, such as e.g., 2, 3 behave similarly
to cis-Rh(phen)2Cl2 + , i.e., have lowest excited states of MC character and
emit accordingly [44, 45].
Thesamelineofreasoningcanbeappliedtorationalizethephotophysical
properties of the bis(2,2 ′ :6 ′ ,2 ′′ -terpyridine)rhodium(III) ion, Rh(tpy) 3+
2 (4),
and analogous complexes. It is well known that, owing to a more unfavorable