Chemistry Reference
In-Depth Information
1
IL
1
LF
30
25
k
isc
'
3
LF
2
1
MLCT
k
isc
20
k
rxn
3
LF
1
3
MLCT
k
nr
15
hν'
k
nr'
h
ν
k
nr
''
k
rxn
'
10
k
p
5
1
GS
0
Figure 8.11
Jablonski-type diagram of [(bpy)
2
Ru(NH
3
)
2
]
2+
. bpy = 2,2
-bipyridine,
1
GS =
singlet electronic ground state,
1
MLCT = singlet metal to ligand charge transfer excited state,
3
MLCT = triplet MLCT excited state,
1
IL = singlet internal ligand excited state,
3
LF = triplet
ligand fi eld excited state. Relative energies are adapted from Singh and Turro
22
′
1
IL
30
k
ic
25
1
MLCT
3
LF
20
k
isc
15
3
MLCT
hν'
hν
10
k
p
hν''
k
nr
5
1
GS
0
Figure 8.12
Jablonski-type diagram of [Os(bpy)
3
]
2+
. bpy = 2,2
-bipyridine,
1
GS = singlet elec-
tronic ground state,
1
MLCT = singlet metal to ligand charge transfer excited state,
3
MLCT =
triplet MLCT excited state,
1
IL = singlet internal ligand excited state. Relative energies are
adapted from Kober, Caspar, Lumpkin and Meyer
24
′
electronic absorption spectra of Os(II) polyazine complexes. The low energy tail is
due to direct population of the
3
MLCT state (Figure 8.12).
24
The larger spin - orbit
coupling constant also enhances decay of the
3
MLCT state to the
1
GS. Unlike the
Ru(II) counterparts, Os(II) polyazine
3
LF states are not thermally accessible from
the
3
MLCT state. Therefore, excitation of the Os(II) chromophore with visible light
generally does not result in ligand substitution. Chromophores based on Ru(II) and
Os(II) polyazine complexes have found great utility in the study of DNA
photomodifi cation.
Rhodium Polyazine Complexes
Rhodium polyazine complexes have distinct, reactive electronic excited states that
make them attractive as PDT agents. As with other transition metal polyazine com-
plexes discussed in this chapter, the ligand environment around the central rhodium
has major impact on the ES properties. Mononuclear tris(chelate) Rh(III) polyazine
complexes are potent light absorbers in the UV region of the spectrum due to strong
