Photoinduced processes in a light-harvesting array PBI-NI
4, made of a central perylene bisimide (PBI)
withfour appended naphthalene imide (NI) units, have been studied in toluene by several spectroscopic techniques,and the steps of energy dissipation have been identified. The singlet excited states
1PBI (
max = 960 nm,
![](/images/gifchars/epsilon.gif)
= 40 000 M
-1 cm
-1) and
1NI (
max = 810 nm,
![](/images/gifchars/epsilon.gif)
ca. 4 000 M
-1 cm
-1) and the charge-separated statePBI
--NI
4+ (
max = 775 nm,
![](/images/gifchars/epsilon.gif)
= 80 000 M
-1 cm
-1)
were identified as reaction intermediates. In the arrayPBI-NI
4, energy transfer from the peripheral
1NI to the PBI core
was sho
wn to compete efficiently (90%)
with electron transfer from the NI unit to the PBI unit. Subsequently,
1PBI displays a slo
w electron abstraction(
k = 4.6 × 10
8 s
-1) from the NI unit to form the charge-separated state PBI
--NI
4+,
which competes
withemission of light energy from the PBI core. The CS state PBI
--NI
4+ decays faster (
k = 2.6 × 10
9 s
-1) thanit is populated, preventing any back reaction to re-form the singlet excited state localized on PBI.