Chemistry Reference
In-Depth Information
quadricycline groups in as little as 20 s. The stored thermal energy of the irradiated polymers was
found to be 32-52 kJ/mol.
10.6.1.2 Copolymers of Methacrylates with Cholesteric Monomers
Groups, like 6-oxo-1,6-dihydropyrimidin-3-ium-4-oleates, are light-sensitive and undergo intramolecu-
lar photo-cyclization to bis-
b
-lactams when irradiated with UV light between 320 and 490 nm [
189
].
R'
R'
R'"
R"
R"
R'"
N
NN
N
hν
O
O
R'"
O
O
R""
This was utilized to form copolymers of methacrylates with colesteric monomers [
190
]. An
example of such copolymers and the rearrangement is shown below [
190
]:
n
m
n
m
O
C
O
O
C
O
UV ligh
t
O
O
O
O
(CH
2
)
4
(CH
2
)
4
(CH
2
)
4
(CH
2
)
4
O
C
S
O
C
S
N
O
O
O
N
O
N
N
(CH
2
)
3
(CH
2
)
3
O
O
C
2
H
5
CH
3
C
2
H
5
CH
3
C
C
CH
3
CH
3
H
H
(CH
2
)
3
(CH
2
)
3
It was found that the rate of photo-rearrangement is affected by the length of the alkyl side group in the
5 position of the pyrimidinium oleate and by the embedding of a chromophore, as shown above [
190
].
In photosynthesis, antenna pigments harvest energy and transfer it into a reaction center for redox
reactions [
191
]. Different antenna chromophores that surround the reaction center are arranged
morphologically in an order of energy gradient [
192
-
194
]. Such an arrangement allows the energy
to be sequentially transferred and efficiently funneled into reaction centers over small distances in the
direction of decreasing band gaps. Considerable research has been carried out on means to develop
the sequential multistep energy transfer systems. This was done not just to mimic the natural light-
harvesting process [
192
-
194
], but also for possible applications and use in optoelectronic and
biological systems [
195
]. It is speculated that a conjugated polymeric backbone, with well-designed
interruptions of conjugation by insulating spacers, might allow tuning the emission properties and by
providing an alternate model [
196
].
