Synthesis and Self-Assembly
of Perylenetetracarboxylic
Diimide Derivatives with Helical Oligo(l‑lactic acid)<sub><i>n</i></sub> Segments
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Abstract
Three perylenetetracarboxylic diimide (PDI) derivatives
consisting
of a short oligo(l-lactic acid)<sub><i>n</i></sub> (O-LLA) segment at one imide nitrogen were synthesized. The polymers
were characterized by <sup>1</sup>H NMR and gel permeation chromatography
(GPC). Their properties were investigated by differential scanning
calorimetry (DSC), X-ray diffraction (XRD) experiments, scanning electron
microscopy (SEM), electronic absorption, and circular dichroism (CD)
spectroscopy. The self-assembly behavior of these PDIs in molten state
as well as in solvent was examined. It was found that the structure
and the morphology of the self-assembly of these polymers depend on
the relative length of the O-LLA segment. The PDIs with longer O-LLA
chains present liquid crystal properties with an obvious phase transition
from disordered phase to an ordered (α) phase, which cannot
be found for the PDIs with short O-LLA segments. The long O-LLA segments
also caused a left-handed helicity for the aggregates of the PDIs
from solution. This research demonstrated that one can control the
order, aggregation mode, and morphology of the molecular aggregates
by changing the length of the O-LLA chains. This information can be
useful in the design of new organic materials that exhibit molecular
aggregation