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0
0
=- DD
H
RT
S
R
ln
K
(5.3)
Self-assemblies also impart electronic communication among
the chromophoric units as the optical emission color can be tuned
from a dynamic
stacked molecular assembly in the solution.
Consequently, green, yellow, orange, and red photoluminescence
was observed by driving the size regime of a perylene-derivative
molecular assembly from individual molecules to nanocrystalline
assemblies.
π−π
-molecules
forming open-ended one-dimensional stack is actually very general
and can be widely applied to macrocycle systems such as those listed
in the review [10]. For example, phenylene ethynylene macrocylces
self-organize into nanostacks in various solvents (Fig. 5.3). The
equilibrium constants of the self-assembled macrocycle stacks
varies with solvents:
The principle outlined here about large planar
π
1
1
K
= 50 M
for CHCl
, 350 M
for THF, 1200
SA
3
for acetone [11,12]. Again, as the
concentration of the macrocycles increases, the nuclear magnetic
resonance peaks of the aromatic protons shift upfield, indicating a
cofacial, nearly concentric
M
1
for benzene, and 15000 M
1
π−π
stacking of the macrocycles [12].
R
K
R
R
K
K
etc
R = CO 2 (CH 2 CH 2 O) 3 CH 3
R
R
R = CH 2 O(CH 2 CH 2 O) 3 CH 3
R = O(CH 2 CH 2 O) 3 COCH 3
R
Figure 5.3
Schematic diagram depicting the intermolecular association
of macrocycles results in dynamic
π
-stacks in the solution.
5.3
Folding of Perylene Oligomers: Tunable
Nanosolenoids
5.3.1
To Fold or to Assemble?
Folding is defined as intramolecular association among various
regions of a macromolecule. Similarly, molecular self-assembly is
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