Dissertation

|1.9 Multicomponent Systems from Fundamental Building Blocks|
**[Ru(bpy) 3 ] 2+
reductive quenching
Q D
ISC
Q A
oxidative quenching
-
Q A
+0.84 V
*[Ru(bpy) 2 (bpy - )] 2+
-0.86 V
Q D
+
[Ru(bpy) 3 ] +
S A
oxidative regeneration
-1.28 V
-
S A
hν
λ max = 450 nm
ε = 14600 l/mol cm
hν'
* Q
τ = 0.6 µs
E = 2.12 eV
λ [Ru(bpy) 3 ] 3+
max = 600 nm energy
φ = 0.04 transfer
Q
S D
[Ru(bpy) 3 ] 2+
S D
+
reductive regeneration
+1.26 V
Figure 19: Relevant energy and electron transfer processes of [Ru(bpy) 3 ] 2+ . After photoexcitation
the spin allowed 1 MLCT state **[Ru(bpy) 3 ] 2+ is reached. *[Ru(bpy) 2 (bpy - )] 2+ represents the longliving
spin-forbidden 3 MLCT state which is existent after intersystem crossing. During the lifetime
of 600 ns different quenching processes may occur by the reaction with a quencher Q, followed
by ground state redox chemistry with a substrate S. The redox potentials are given in aqueous
solution, referenced vs. SCE. [36]
The correlation between spectroscopy and electrochemistry is depicted in figure 19. It is known
that the energy available to the 3 MLCT-excited *[Ru(bpy) 3 ] 2+ (E 0-0 = 2.12 eV) by far exceeds the
energy necessary for over all water spitting (1.23 eV per transfered electron). This energy can be
tapped during the lifetime of the excited state via different quenching mechanisms and leads to the
regeneration of the ground state species of the sensitizer, if the quenching process involves only
energy transfer processes (EnT). The biradical nature of the MLCT results at the same time in a
fairly high oxidizing and reducing power (+0.84 and -0.86 V in water vs. NHE) of the excited
complex. Therefore, it is also possible to tap the excited state energy in an electron transfer
|28|