Chemistry Reference
In-Depth Information
transfer,
k
en
(Equation 8.9); and photochemical reaction,
k
rxn
(Equation 8.10 ); where
Q = quencher, ED = electron donor, EA = electron acceptor.
I
a
+→
LA
h
ν
*LA
(8.3)
k
*LA
→
LA
+
h
ν
′
(8.4)
k
→
*LA
nr
LA
(8.5)
k
′
*LA
+
Q
nr
→
LA
+
Q
(8.6)
k
*LA
+
ED
→
et
LA
−
+
ED
+
(8.7)
k
′
*LA
+
EA
et
→
LA
+
+
EA
−
(8.8)
k
*LA
+→
Q
en
LA
+
*Q
(8.9)
k
*LA
+
reactant
rxn
→
photoproducts
(8.10)
Current research efforts toward PDT agents study the photochemistry of an
excited chromophore with DNA. Transition metal polyazine complexes have a rich
history of photochemistry with DNA, focusing strong research efforts. These efforts
have given rise to recent discoveries of previously unknown photochemistry. The
fi eld is expanding rapidly to accommodate increasing interest in DNA photochemi-
cal modifi cation and inorganic-based PDT. In addition, information about funda-
mental photophysical properties is being uncovered.
Excited State Electron Transfer Theory
Reductive and oxidative quenching of *LA is driven by the relative redox potentials
of the ED or EA and *LA. The *LA reduction
E
( * LA
n
/LA
n
− 1
) and * LA oxidation
E
( * LA
n
/LA
n
+1
) potentials are estimated with the following equations:
E
(*LA
n
LA
n
−
1
)
≈
E
( LA
n
LA
n
−
1
)
− ∆
E
00
−
(8.11)
(
)
≈
(
)
+∆
E
*LALA
n
n
+
1
E
LALA
n
n
+
1
E
00
−
(8.12)
where
E
(LA
n
/LA
n
− 1
) and
E
(LA
n
/LA
n
+1
) are the respective fi rst reduction and oxida-
tion potentials in V of the GS chromophore, and
E
0− 0
is the difference of energy
between lowest vibronic states of the GS and ES in eV (see Figure 8.4). The
∆
∆
E
0− 0
is commonly estimated from the
em
with a Stokes shift applied to account for the
shift of the excited state energy surface relative to the ground state. The rate of ES
quenching is governed by the driving force of electron transfer as described by
Marcus.
45
For a bimolecular reaction under pseudo-fi rst order conditions:
λ
max
[
]
[
]
>>
[
]
ED
or EA
ES
o
o
