Chemistry Reference
In-Depth Information
30
1
IL
k
isc
25
1
MMLCT
k
isc'
k
isc"
3
IL
20
1
MM-MM
3
MMLCT
15
3
MM-MM
k
rxn
10
h
ν
k
rxn'
k
nr
5
1
GS
0
Figure 8.15
Jablonski-type diagram of cis-[Rh
2
(
m
-O
2
CCH
3
)
2
(dppz)
2
]
2+
. dppz = dipyrido[3,2-
a:2
-c]phenazine,
1
GS = singlet electronic ground state,
1
IL = singlet internal ligand excited
state,
1
MMLCT = singlet metal-metal to ligand charge transfer state,
1
MM-MM = Rh-Rh(d
p
*-
d
′
,3
′
*) state. Relative energies are adapted from Angeles-Boza, Bradley, Fu, Wicke, Bacsa,
Dunbar, Turro
33,82
Σ
DNA thermal binding properties of the well known complex
cis -
[Pt(NH
3
)
2
Cl
2
]
(cisplatin).
30,31
Dirhodium(II) complexes possess unique ES compared to the mononuclear
Rh(III) complexes due to the strong electronic coupling of the two metal centres.
Complexes of the form [Rh
2
( m - O
2
CCH
3
)
4
] absorb weakly in the near UV region
owing to a low lying Rh-Rh(dp * )
Rh - Rh(d s * ) (MM - MM) transitions (Figure
8.15 ).
32
Inclusion of ligands with stabilized p * - acceptor
→
orbitals,
e.g.
dibenzo[
h,j
]dipyrido[3,2 -
a
:2
′
,3
′
-
c
]phenazine (dppz), gives complexes with transi-
tions at
dppz( p * ) charge
transfer transitions (MMLCT).
33
The
3
MMLCT state is thought to be a long-lived
state with an oxidized dirhodium core. These complexes display DNA photooxida-
tion reactions, consistent with reaction of the
3
MMLCT state.
∼
430 nm attributed to IL transitions and Rh-Rh(dp * )
→
Excited States of Polyazine Bridged R u - R h Complexes
Polyazine bridged, mixed-metal supramolecules have been developed that incorpo-
rate multiple metal centres and have more complicated photophysics than the
mononuclear analogues.
34
The mixed-metal complexes often retain some ES proper-
ties of the subunits used to assemble the supramolecule. Metal centres with strong
electronic coupling, e.g. di-Rh(II) complexes above, have electronic transitions that
involve orbitals delocalized over the metal centres. At the other extreme, metal
centres that are covalently linked, but without strong electronic coupling, behave
like the mononuclear analogues. Ru(II)-Rh(III) dyads linked via an alkyl tether
have electronic properties consistent with each subunit, indicating weak electronic
interaction between coupled chromophores.
35 - 39
The polyazine bridged complexes
have intercomponent interactions, giving rise to states that are unique to the
supramolecular complex without full delocalization of orbitals.
Mixed-metal supramolecules that have weakly to moderately coupled metal
centres exhibit unique ES with interesting ES dynamics, giving rise to useful pho-
