DOI: 10.1002/asia.202001041
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Ultralow-Molecular-Weight Stimuli-Responsive and Multifunctional
Supramolecular Gels Based on Monomers and Trimers of
Hydrazides
[a]
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Abstract: The simpler, the better. A series of simple, neutral
and ultralow-molecular-weight (MW: 140–200) hydrazide-
derived supramolecular gelators have been designed and
synthesized in two straightforward steps. For non-conjugated
cyclohexane-derived hydrazides, their monomers can self-
assemble to form gels through intermolecular hydrogen
bonds and dipole-dipole interactions. Significantly, conju-
gated phthalhydrazide can self-aggregate into planar and
circular trimers through intermolecular hydrogen bonds and
then self-assemble to form gels through intermolecular π–π
stacking interactions. It is interesting that these simple
gelators exhibit unusual properties, such as self-healing,
multi-response fluorescence, and visual and selective recog-
2
À
nition of chiral (R)/(S)-1,1’-binaphthalene-2,2’-diamine and S
through much different times of gel re-formation and blue-
green color change, respectively. These results underline the
importance of supramolecular gels and extend the scope of
supramolecular gelators.
Introduction
dicarboxylate gelator can form stable gels in nitrobenzene
[8a]
solvent. Choline chloride/phenylacetic acid can be used as
[1]
[9a]
Low-molecular-weight gelators (LMWGs) (typically with molec-
gelation solvent for isoleucine and tryptophan. In addition,
ular weights, MW<3000) have attracted a lot of attention due
dipole-dipole/donor-acceptor interactions acting as auxiliary
[2]
to their wide applications, such as multi-responsive sensing,
forces can help neutral π-conjugated molecules to form gels in
[3]
[4]
[1h,5b,10]
self-healing,
optoelectronics.
environmental
protection,
and
normal solvents.
[1f,h,5]
The LMWGs, which self-assemble into 3D
Owing to their strong intermolecular hydrogen bonds,
hydrazides have been widely used as precursors to construct
networks through intermolecular noncovalent interactions,
including hydrogen bonds, π–π stacking, electrostatic, and van
der Waals interactions, are capable of immobilizing solvent
molecules and forming supramolecular gels. Especially,
supramolecular gels are recently used as a chiral matrix and
amplification to discern the subtle stereochemical differences
[1,11]
LMWGs.
Most of these LMWGs have complicated structures
and need tedious organic synthesis. In this study, in order to
simplify LMWGs, we combining the effects of dipole-dipole and
aggregation-induced oligomer have developed a novel and
convenient strategy to prepare a series of neutral hydrazide-
derived LMWGs (6 samples, Scheme 1). The introduction of
electron-rich hydrazide moieties that are capable of forming
hydrogen bonded assemblies is essential for gelation. Chair-
shape cyclohexane would not only increase molecular asymme-
try and dipole moment (μ) to assist to form gels but also
incorporate chirality for chiral recognition. The presence of
benzene ring would lead to a planar structure for aggregation-
induced trimers that have bigger π-conjugated systems to form
functional π-gelators through intermolecular π–π stacking
interactions. Although these LMWGs containing one
cyclohexane or benzene are very simple and their molecular
weights (MW) are within the range of 140–200, they have some
useful applications in multi-response fluorescence, visual chiral
recognition, and self-healing. First of all, to the best of our
knowledge, this is the first example of trimer-based LMWGs and
the simplest example of π-gelators.
[6]
between enantiomers for visual chiral recognition. The basic
principle of designing these functional LMWGs, such as π-
[1h]
gelators,
is the incorporation of some long side groups
including long alkyl chains, amide, urea peptides, cholesterol,
sugar, or steroidal groups into the π-conjugated cores. How-
ever, designing these LMWGs is still a daunting task and most
of them have been found by an accident rather than by design.
Therefore, simple, straightforward, and low-cost LMWGs are
highly intriguing and in great demand. It should keep in mind
that the simpler molecules always mean weaker intermolecular
noncovalent interactions, which are harmful for gelation. In
[7]
order to solve this problem, organic salts that have much
stronger charge-assisted hydrogen bonds than normal neutral
[8]
organic compounds are adopted as gelators and gelation
[9]
solvents. For example, imidazolium hydrogen cyclobutane-1,1-
[
a] D. Wu, J. Song, L. Qu, W. Zhou, L. Wang, Prof. X. Zhou, H. Xiang
College of Chemistry
Sichuan University
Chengdu, 610041 (P. R. China)
Results and Discussion
E-mail: xianghaifeng@scu.edu.cn
All hydrazides were prepared straightforwardly in two steps
with favorable yields (Scheme 1), according to our previous
Chem Asian J. 2020, 15, 1–10
1
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