Chemistry Reference
In-Depth Information
1
IL
35
k
isc
30
3
IL
25
hν
20
k
p
15
k
nr
10
5
1
GS
0
Figure 8.13
Jablonski-type diagram of [Rh(phen)
3
]
3+
. phen = 1,10-phenathroline,
1
GS = -
singlet electronic ground state,
1
IL = singlet internal ligand excited state. Relative energies are
adapted from Crosby and Elfring
26
1
IL
k
isc
'
30
1
LF
3
IL
25
k
isc
3
LF
2
20
k
i
c
hν'
15
hν
3
LF
1
k
p
10
k
rxn
k
nr
5
1
GS
0
Figure 8.14
Jablonski-type diagram of [(phen)
2
RhCl
2
]
+
. phen = 1,10-phenathroline,
1
GS =
singlet electronic ground state,
1
IL = singlet internal ligand excited state,
3
LF = triplet ligand
fi eld excited state. Relative energies are adapted from Demas and Crosby
27
IL transitions. These Rh(III) complexes lack the visible light absorption bands as
their MLCT transitions occur at much higher energy than analogous Ru(II) and
Os(II) systems (Figure 8.13).
26
Coincidently, the complexes emit from a
3
IL state.
Bis(chelate) polyazine complexes of Rh(III) with a
cis
- Rh
III
X
2
moiety, where
X is a halide, also absorb only in the UV and are emissive in low temperature
glasses.
27
A weak absorption band observed between 350-400 nm arises from LF
transitions for the [(TL)
2
RhX
2
]
+
systems. The emission from these complexes, when
excited into the IL or LF bands, is broad and signifi cantly Stokes shifted relative
the lowest absorption band (
14 000 cm
− 1
).
28
The initially populated
1
LF state inter-
system crosses to an upper
3
LF
2
state (Figure 8.14). The
3
LF
2
state decays by internal
conversion to the emissive
3
LF
1
state. At room temperature, photoaquation (
k
rxn
)
competes with nonradiative decay to give the mono- and disubstituted solvato
complexes, [[(TL)
2
RhX(S)]
2+
and [(TL)
2
Rh(S)
2
]
3+
(S = solvent).
23,29
Morrison and
coworkers have exploited this decay pathway to photobind to DNA, mimicking the
∼
