Biomedical Engineering Reference
In-Depth Information
a
NN
P = 3.0 D
P = 0
R
N
l
N
R
l
' or
D
T
0.9 nm
R
R
0.55 nm
b
R
R
l
D
T
N
C
N
N
C
N
X
X
c
l
R
2
R
2
N
N
O
O
l
'
R
1
R
1
d
O
O
R
O
R
O
l
O
l
'
O
R
R
O
O
Fig. 12
Examples of chromophores that display photochemically- induced transitions. (
a
) Reversible
trans
(
left
) and
cis
(
right
) photo-isomerization of azobenzene. (
b
) Dissociation of triphenylmethane
leucoderivatives into an ion pair under ultraviolet irradiation. (
c
) Reversible photo-isomerization of
spirobenzopyran derivatives. (
d
) Reversible photodimerization of cinnamoyl group
These light sensitive triggers could, in principle, be incorporated into amphiphilic
copolymers suitable for polymer vesicle formation.
Azobenzene derivatives are the most studied photoactive groups. The azo group
can undergo reversible isomerization between the
trans
and
cis
configurations by
light and heat (see Fig.
12a
). The
trans
isomer is thermodynamically more stable in
common conditions. The
cis
isomer obtained by light (usually UV) irradiation is
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