Angewandte
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resulting polyisocyanides was solely from the single-handed
taining Py- and Np-probes were facilely prepared with
helicity, and inexistence of any other chiral moieties on the
chain ends nor on the pendants. This kind of polymers are
controlled molecular weights (M = 19.6–76.2 kDa) and low
n
polydispersity (M /M = 1.20–1.26) (Table S1, Supporting In-
w
n
ideal systems to investigate the helicity- and M -driven self-
sorting and assembly processes. In this work, we designed and
synthesized a family of single-handed helical polyisocyanides
formation (SI)). For comparison, left-handed M-poly-1ms and
right-handed P-poly-1ms without fluorescent labelling were
also prepared. The chemical structures of these polymers
were fully characterized by size exclusion chromatography
n
with controlled M and low polydispersity bearing pyrene
n
1
(
Py) and naphthalene (Np) probes on the pendants. Fluores-
(SEC), H NMR, and FT-IR as well (Figure S1–S13, SI).
cence resonance energy transfer (FRET) and atomic force
microscope (AFM) studies revealed these polymers can
recognize themselves and self-sort in solution, solid state, in
gel and on gel surface, through the discrimination on their
The helix-sense of the synthetic polymers was verified by
absorption and circular dichroism (CD) spectroscopies, and
AFM analyses. As expected, left-handed M-poly-1150-Py and
M-poly-1150-Np showed intense negative CD at the first
Cotton band. While right-handed P-poly-1m-Np and P-poly-
1m-Py showed positive CDs at the same absorption area, and
were mirror image to that of M-poly-1m-Py and M-poly-1m-
Np, regardless of the fluorescence probes (Figure S14, SI).
The absolute molar CD intensities at 364 nm (De364) that
quantitative reflect the enantiomeric excess of one-handed
helicity and M . Polyisocyanides with the same handedness
n
can recognize themselves and self-assemble into well-defined
two-dimensional (2D) smectic architectures. While the poly-
mers with opposite handedness or largely different in M are
n
repulsive to each other and couldnꢀt aggregate together.
Moreover, owing to strong intermolecular attraction, helical
polymers with the same helicity can form a self-standing gel in
various solvents. The gels could also recognize themselves,
and selectively adhere together and self-healing based on the
À1
À1
helix (ee ) were up to 20 M cm for all the polymers. Thus,
h
the eeh values of these polymers were higher than 99%,
confirmed the single-handed helix-sense of the main
[32,48]
discrimination on helicity and M . The distinct 2D-smectic
chain.
Additional evidence for the single-handed helical
n
architectures with interesting self-recognition and self-healing
properties endow the helical polymers with great potentials in
many fields such as liquid crystallization, self-healing smart
materials, stereoselective aggregation, photonic crystals, and
structure came from the direct AFM observations. Only left-
handed polymer chains could be observed on the AFM image
of M-poly-1m-Py, while AFM images of P-poly-1m-Py
polymers only showed right-handed helical chains (Fig-
[55,56]
in circularly polarized luminescence.
ure S15, SI). The ee values of the polymers estimated by
h
AFM were generally agree with the CD analyses, and were all
[32,48]
up to 99%.
These studies convinced the single-handed
Results and Discussion
helicity of the synthetic polyisocyanides bearing Py- and Np-
probes. Note that all these polymers have the same chemical
structure except for the helicity and fluorescent probes. The
Synthesis of single-handed helical polymers. As displayed
in Scheme 1, single-handed helical polyisocyanides bearing
Py or Np probes on the pendants were prepared via the helix-
sense-specific living copolymerization of achiral isocyanide
monomer (1) with 1-Py or 1-Np, respectively bearing Py- or
II
chiral ligand and the Pd -terminus were removed after the
[32]
polymerization. The helical structures were quite stable, no
racemization was observed in THF at 558C for one week,
probably due to the stabilization by the long alkyl tails and
II
[48]
Np-substituent (ca. 10% content), using Pd catalysts carry-
amide functions (Figure S16, SI).
ing S- or R-2,2’-bis(diphenylphosphino)-1,1’-binaphthalene
Helicity-driven self-sorting. Self-sorting capability of the
[32]
(S- or R-BINAP) ligands. Because of the living and helix-
helical polyisocyanides was first investigated in THF by
[23]
sense specific characters of the polymerization, a series of left-
handed helices (M-poly-1m-Py, M-poly-1m-Np) and right-
handed polymers (P-poly-1m-Py, and P-poly-1m-Np) con-
FRET method. Py-Labelled, right-handed P-poly-1150-Py
and left-handed M-poly-1150-Py were, respectively added to
two THF solutions of Np-labeled right-handed P-poly-1150-Np
under the same condition (Figure 1a). The M of the three
n
polymers were almost the same (Table S1, SI). Fluorescence
spectra of the two mixtures were excited at 290 nm and the
emission intensities at 435 nm of Py and 336 nm of Np were
monitored. Figure 1b showed the time-dependent fluores-
cence spectra of the mixture of P-poly-1150-Py with P-poly-
1150
-Np. It was found that the Np-emission at 310–390 nm was
gradually decreased, accompanied by a dramatically en-
hanced Py-emission at 390–550 nm. After ca. 144 h, the
fluorescence spectra reached to a maximum and became
constant. The remarkable FRET indicated the dynamic chain
exchange and aggregation of the two polymers. In sharp
contrast, almost no FRET could be detected on the mixture of
P-poly-1150-Np and M-poly-1150-Py under the same conditions,
even it was incubated for more than one week (Figure 1c).
The structure of P-poly-1150-Py and M-poly-1150-Py was similar
except for the helicity, thus the different FRET behaviors of
Scheme 1. Synthesis of the single-handed helical polymers bearing Np-
or Py-probes.
Angew. Chem. Int. Ed. 2021, 60, 7174 – 7179
ꢀ 2021 Wiley-VCH GmbH
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