Chemistry Reference
In-Depth Information
1
ES
k
isc
3
ES
k
f
k
p
E
k
ic
h
ν
k
nr
1
GS
Figure 8.5
Jablonski diagram illustrating relative energies of states. Each bar ( ) represents
the potential energy surface of an electronic state with lines above the state meant to refl ect
excited vibronic states. ES are excited states and GS is the ground state. Arrows represent
electronic excited state decay via fl uorescence (
k
f
), internal conversion (
k
ic
), intersystem cross-
ing (
k
isc
), phosophorescence (
k
p
) and nonradiative (
k
nr
) pathways
k
isc
h
ν
E
1
GS
1
ES
3
ES
Figure 8.6
Orbital representation of intersystem crossing (
k
isc
) from singlet excited state (
1
ES)
to triplet excited state (
3
ES)
emitting ES. Nonradiative relaxation of an ES to the ground state is sometimes
expressed by
k
nr
.
8.2.3 Electronic Excited States and Unimolecular Decay of Transition
Metal Polyazine
Transition metal polyazine complexes are potent light absorbers in the ultraviolet
(UV) and visible region of the spectrum (Figure 8.7.)
18
All polyazine complexes
absorb UV light strongly due to intense internal ligand (IL) transitions of the aro-
matic ligands (Figure 8.8). IL transitions are called ligand centered (LC) in some
literature. Ruthenium(II) and osmium(II) polyazine complexes absorb strongly in
the visible region and have low-lying ES that are typically emissive, long-lived and
reactive.
19
Mononuclear Rh(III) polyazine complexes absorb strongly in the UV-A
region due to IL transitions. The ES of rhodium(III) and dirhodium(II) polyazine
complexes have reactivity that is strongly coupled to the type of polyazine ligands
