Chemistry Reference
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Fig. 11
Bilayer packing of amphiphilic OPV molecules. Reprinted with permission
from [74].
©
2005 American Chemical Society
in smectic C (S
C
) and smectic A (S
A
) phases. The interlayer spacing is ap-
proximately equal to the fully extended lengths of the molecules, indicating
significant interdigitation and/or tilt within a bilayer smectic structure. The
X-ray data confirmed that OPV amphiphiles form an interdigitated bilayer
smectic phase as shown in Fig. 11. Liquid crystallinity will be used to control
OPV aggregation, influencing exciton mobility, fluorescence, and potentially
leading to improved charge carrier mobility in heterojunction solar cells or en-
abling more efficient, polarized emission from organic light-emitting diodes.
Very recently, Lin et al. synthesized asymmetrical molecules consisting
of a novel conjugated aromatic core containing fluorene, thiophene, and
biphenyl groups and two kinds of PEO chains (
DP
= 17 and 44) on one
side and alkoxy groups with different lengths (- OC
8
H
17
and - OC
16
H
33
)on
another side of the rigid core and their mesophases characterized [75]. Asym-
metrical amphiphilic molecules based on short PEO chain (
DP
= 17) display
the smectic phases. However, amphiphilic molecules based on longer PEO
chain (
DP
= 44) show two kinds of columnar phases, hexagonal columnar
and rectangular columnar. The immiscibility between the hydrophilic flexi-
ble chains and the hydrophobic rods leads to stronger lateral interaction of
rigid rods and induces the smectic phases. By increasing the hydrophilic ethy-
lene oxide units, the immiscibility increases and microphase separation is
enhanced to form more order columnar phases.
3.2
ABA Coil-Rod-Coil Triblock Copolymers
In the case of symmetric coil-rod-coil molecule, the rod segment is con-
nected with coil segments at both ends. This gives rise to the formation of the
liquid crystalline structure with higher interfacial area in comparison with
rod-coil diblock systems at similar coil volume fraction. For example, the
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