The steric hindrance controlled [2]pseudorotaxanes constructed by V-type stilbene dyes?CB[7]

Article abstract of DOI:10.1080/10610278.2018.1538515

In this paper, five V-type stilbene dyes (VD, 1a-1e) that had unchanged dimethylamino phenylethenyl (DMPE) arm as inclusive location with CB[7] and another arm with different steric hindrance aryloxyethyl (AE) group were designed and synthesized. Their inclusive characteristics and stability to CB[7] were studied. Fluorescence spectroscopy and ¹H NMR method were used respectively to study the inclusive characteristics of 1a?CB[7], 1b?CB[7], 1c?CB [7], 1d?CB[7] and 1e?CB[7]. Fitting curves results of fluorescent titration indicated that 1:1 complexes between CB[7] and VD were constructed, and their inclusive constants were calculated respectively. The order of inclusive constants K_1a?CB[7]>?K_1b?CB[7]>?K_1c?CB[7] >?K_1d?CB[7] was consistent with the magnitude of the steric hindrance, however, 1e did not include with CB[7]. Therefore, a series of steric hindrance controlled [2]pseudorotaxanes were constructed.

Full text of DOI:10.1080/10610278.2018.1538515

Supramolecular Chemistry
ISSN: 1061-0278 (Print) 1029-0478 (Online) Journal homepage: http://www.tandfonline.com/loi/gsch20
The steric hindrance controlled
[2]pseudorotaxanes constructed by V-type stilbene
dyes⊂CB[7]
Qijing Gu, Zihui He, Qianxia Pan, Ziyi Lin, Jie Sun, Qiang Wang & Haibo Wang
To cite this article: Qijing Gu, Zihui He, Qianxia Pan, Ziyi Lin, Jie Sun, Qiang Wang & Haibo
Wang (2018): The steric hindrance controlled [2]pseudorotaxanes constructed by V-type stilbene
dyes⊂CB[7], Supramolecular Chemistry, DOI: 10.1080/10610278.2018.1538515
To link to this article: https://doi.org/10.1080/10610278.2018.1538515
Published online: 27 Oct 2018.
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SUPRAMOLECULAR CHEMISTRY
https://doi.org/10.1080/10610278.2018.1538515
ARTICLE
The steric hindrance controlled [2]pseudorotaxanes constructed by V-type
stilbene dyes⊂CB[7]
Qijing Gua, Zihui Hea, Qianxia Pana, Ziyi Linb, Jie Sunb, Qiang Wanga and Haibo Wanga
b
aCollege of chemistry and molecular engineering, Nanjing Tech University, Nanjing, China; College of food science and light Industry,
Nanjing Tech University, Nanjing, China
ABSTRACT
ARTICLE HISTORY
Received 18 May 2018
Accepted 15 October 2018
In this paper, five V-type stilbene dyes (VD, 1a-1e) that had unchanged dimethylamino pheny-
lethenyl (DMPE) arm as inclusive location with CB[7] and another arm with different steric
hindrance aryloxyethyl (AE) group were designed and synthesized. Their inclusive characteristics
KEYWORDS
1
and stability to CB[7] were studied. Fluorescence spectroscopy and H NMR method were used
Cucurbit[7]uril; V-type
stilbene dyes; steric
hindrance; fluorescence
respectively to study the inclusive characteristics of 1a⊂CB[7], 1b⊂CB[7], 1c⊂CB [7], 1d⊂CB[7]
and 1e⊂CB[7]. Fitting curves results of fluorescent titration indicated that 1:1 complexes between
CB[7] and VD were constructed, and their inclusive constants were calculated respectively. The
order of inclusive constants K1a⊂CB[7]> K1b⊂CB[7]> K1c⊂CB[7] > K1d⊂CB[7] was consistent with the
magnitude of the steric hindrance, however, 1e did not include with CB[7]. Therefore, a series of
steric hindrance controlled [2]pseudorotaxanes were constructed.
Introduction
TSS⊂HOCB[6]. The results suggested that ethanol and
acetonitrile could remarkably enhance the fluorescence
intensities of TSS and TSS⊂HOCB[6].
Mock et al. (17) had carried out an experiment to
investigate the binding of small alkyl- and aryl-substi-
tuted ammonium ions within the cavity of cucurbituril,
and discovered that cucurbituril showed strong selec-
tivity to different alkyl chain length.
Buschmann et al. (18, 19) had studied the inclusion
of amino acid, amino alcohol, fatty alcohol, fatty acid,
and aliphatic nitrile with CB[6] using thermometric
titration. They discovered that the number of methy-
lene and group polarity had almost no effect on the
stability of inclusive complexes constructed from amino
acid, fatty alcohol, fatty acid and aliphatic nitrile. But
Accurate assembling between host and guest has played
a significant role in the progress of supramolecular chem-
istry and has been widely used in molecular machines (1),
molecular switches (2), drug delivery (3), and so on. Many
reports have found that assembling location and stability
between host and guest are greatly subjected to the
compatibility of host and guest in terms of molecular
size and shape (4–8). So far, host-guest assembling is
affected by many factors, such as pH (9–11), temperature
(12), light (13, 14), solvent (15) et.al., but the influence of
steric hindrance is rarely reported.
Cong et al. (16) had studied the influence of three
different solvents, such as ethanol, acetonitrile and
acetone, on the fluorescence intensities of TSS and
CONTACT Haibo Wang
wanghaibo@njtech.edu.cn
College of chemistry and molecular engineering, Nanjing Tech University, Nanjing, China
© 2018 Informa UK Limited, trading as Taylor & Francis Group

2
Q. GU ET AL.
the inclusive complex of amino alcohol containing 3
carbons had the highest stability.
purification. Elemental analysis was performed on a
Heraeus CHNO Rapid Analyser. 1H NMR (400 MHz) spec-
tra was recorded with a Bruker DRX 400 spectrometer
with tetramethyl silane (TMS) as an internal reference.
Fluorescence spectra was measured on a Perkin Elmer
LS-55 fluorophotometer.
At present, the inclusion between V-type dye and
cucurbituril has been widely investigated. Zhang et al.
(20) had studied Switchable V-Type [2]Pseudorotaxanes,
the CB[7] ring can be switched between the two sta-
tions of the V-type dye by pH stimuli. Wu et al. (21)
synthesized a [Ru(bpy)3]2+ stopped ‘V’ type guest mole-
cule, which competitively prefers to thread into the
cavity of cucurbit[7]uril to form a pseudo[2]rotaxane.
So far, in terms of the inclusion between the V-type
dyes with two different arms and CB, the effect of the
steric hindrance of one arm on the inclusive character-
istics of another arm was rarely reported.
Synthesis of 2a
In a 250 mL four-necked flask, phenol (18.8 g, 0.2 mol)
and 1,2-dibromoethane (131.6 g, 0.7 mol) were dis-
solved in acetonitrile (100 mL), then the potassium
carbonate (80 g, 0.6 mol) was added. The reaction
mixture was heated to 80 ° and stirred for 18 h. After
completion of reaction (monitored by TLC), the mixture
was allowed to cool to room temperature, filtered, and
the filtrate was concentrated under reduced pressure.
The residual was poured into H2O (200 mL) under
stirring, then allowed to stand overnight. The solid
was collected by filtration and dried under vacuum to
afford 2a (30.8 g, yield 76.5%) as a white solid. 1 H NMR
Therefore, in order to study the influence of steric
hindrance on the characteristics of inclusion between
V-type dyes and cucurbituril, our group had designed
and synthesized the V-type stilbene dyes (VD,1a-1e). In
VD, one arm contains dimethylamino phenylethenyl
(DMPE) unit that can include with CB, and kept
unchanged; another arm contains aryloxyethyl (AE)
unit with different steric hindrance, such as phenyloxy
(1a), tolyloxy (1b), naphthyloxy (1c and 1d) and 9-
anthryloxy (1e). The influence of steric hindrance on
the inclusive characteristics and stability could be stu-
(400 MHz CDCl ) δ 7.33–7.26 (m, 2H), 6.98 (t, J = 7.4,
3
1.1 Hz, 1H), 6.94–6.88 (m, 2H), 4.29 (t, J = 6.3 Hz, 2H),
3.64 (t, J = 6.3 Hz, 2H). Anal. Calcd. For C8H9BrO: C,
47.78%, H, 4.52%, found: C, 48.58%, H, 4.59%.
1
died by the fluorescence spectroscopy and H NMR.
Synthesis of 3a
Experiment
2a (28.2 g, 0.1 mol), 2-methylpyridine (15.6 g, 0.2 mol)
and DMF (100 mL) were added to the four-necked flask
under stirring. The mixture was heated to 100 ° and
stirred for 12 h. After completion of reaction (monitored
by TLC), the ethyl acetate (100 mL) was poured into the
reaction mixture under stirring. The mixture was
allowed to cooling to room temperature, then filtered
under reduced pressure. The solid was washed with
ethyl acetate (50 mL), and dried to afford a white solid
Materials and methods
Cucurbituril[7] is synthesized by glycoluril reacting with
formaldehyde (22, 23). 1a-1e were prepared by using
phenols (phenol, p-methylphenol, α-naphthol, β-
naphthol and 9-anthrol) as the starting materials; syn-
thetic method is similar to the previously described
procedure (shown in scheme 1) (20). All reagents were
commercially available and used without further
Scheme 1. The synthetic procedure of VD (1a-1e).

SUPRAMOLECULAR CHEMISTRY
1
3
1
3a (18.9 g yield 64.2%). H NMR (400 MHz D2O) δ
For 1d (red solid, yield 38.2%). H NMR (400 MHz,
DMSO-d6) δ 8.88 (d, J = 6.2 Hz, 1H), 8.49 (d, J = 8.4 Hz,
1H), 8.38 (t, J = 7.8 Hz, 1H), 7.93 (d, J = 15.6 Hz, 1H),
7.85–7.76 (m, 4H), 7.59 (d, J = 8.9 Hz, 2H), 7.51–7.43 (m,
1H), 7.37 (t, J = 7.8 Hz, 3H), 7.04 (dd, J = 9.0, 2.5 Hz, 1H),
6.69 (d, J = 8.9 Hz, 2H), 5.25 (t, J = 4.6 Hz, 2H), 4.62 (t,
J = 4.7 Hz, 2H), 3.02 (s, 6H). Anal. Calcd. For
C27H27N2BrO: C, 68.20%, H, 5.74%, N, 5.89% found: C,
68.91%, H, 5.80%, N, 6.16%.
10.04–9.93 (m, 1H), 8.31 (m, J = 7.8, 1.4 Hz, 1H), 8.01–
7.91 (m, 1H), 7.83 (m, J = 8.0, 1.5 Hz, 1H), 7.27–7.23 (m,
2H), 6.98 (t, J = 7.3, 1.1 Hz, 1H), 6.88–6.76 (m, 2H), 5.60–
5.48 (m, 2H), 4.64 (t, J = 5.4, 4.0 Hz, 2H), 3.12 (s, 3H).
Anal. Calcd. For C14H16NBrO: C, 57.15%, H, 5.49%, N,
4.76%, found: C, 57.90%, H, 5.55%, N, 4.87%.
1
Synthesis of V-type stilbene dye 1a
For 1e (red solid, yield 27.6%). H NMR (400 MHz,
DMSO-d6) δ 9.15 (d, J = 6.2 Hz, 1H), 8.69 (d, J = 8.4 Hz,
1H), 8.56 (t, J = 7.9 Hz, 1H), 8.13–7.99 (m, 4H), 7.80 (d,
J = 8.6 Hz, 2H), 7.73 (d, J = 8.9 Hz, 2H), 7.56–7.42 (m, 6H),
6.72 (d, J = 9.0 Hz, 2H), 5.55 (t, J = 4.6 Hz, 2H), 4.54 (t,
J = 4.9 Hz, 2H), 2.99 (s, 6H). Anal. Calcd. For
C31H29N2BrO: C, 70.85%, H, 5.57%, N, 5.35% found: C,
71.50%, H, 5.61%, N, 5.70%.
3a (16.2 g, 55 mmol), p-dimethylaminobenzaldehyde
(9.8 g, 66 mmol) and ethanol (100 mL) were added to
the four-necked flask, the mixture was heated to 60 °
under stirring and then piperidine (1.2 mL, 13 mmol)
was added. The reaction mixture was refluxed for 6 h,
then cooled to room temperature. The precipitate was
collected by filtration, and recrystallized from ethanol to
afford a red solid 1a (10.6 g, yield 45.5%). 1H NMR
(400 MHz DMSO-d6) δ 8.84 (d, J = 6.6, 1.4 Hz, 1H),
8.49 (d, J = 8.6, 1.4 Hz, 1H), 8.43–8.34 (m, 1H), 7.94 (d,
J = 15.6 Hz, 1H), 7.78 (d, J = 7.6, 6.3, 1.4 Hz, 1H), 7.73–
7.68 (m, 2H), 7.40 (d, J = 15.6 Hz, 1H), 7.31–7.22 (m, 2H),
6.95 (d, J = 7.3, 1.1 Hz, 1H), 6.92–6.48 (m, 2H), 6.82–6.78
(m, 2H), 5.19 (t, J = 4.8 Hz, 2H), 4.47 (t, J = 4.9 Hz, 2H),
3.05 (s, 6H). Anal. Calcd. For C23H25N2BrO: C, 64.93%, H,
5.94%, N, 6.59% found: C, 65.54%, H, 6.01%, N, 6.90%.
Results and discussion
1H NMR characteristics of the VD⊂ CB[7]
The theoretical value of the CB[7] cavity inner diameter
is about 5.4 Å and the cavity outer diameter theoretical
value is about 7.3 Å. In the neutral aqueous solution, it
is possible for CB[7] to simultaneously encapsulate
both arms of 1a-1d. CB[7] has the high specificity for
alkyl or aryl ammonium ions due to largely electrostatic
ion-dipole attraction (24). The pKa of the dimethyla-
mino phenyl moiety is 2.81 (25), thereby, the dimethy-
lamino unit is completely protonated at pH 2 (26), in
this state, CB[7] only includes on DMPE arm. On the
other hand, CB[7] has a 7.3 Å equatorial width, which is
relatively larger than the distance between the two
branches of VD. So it is impossible for two CB[7] rings
to simultaneously encapsulate both arms of VD to form
a [3]pseudorotaxane due to steric hindrance, which is
proved by the same proton chemical shift of 1a in the
presence of 1.0 and 3.0 equiv of CB[7] in D2O at pD 2
(as shown in Figure 1).
Synthetic procedures of V-type stilbene dyes 1b-1e
VD (1b-1e) were prepared by the procedure similar
to 1a.
1
For 1b (red solid, yield 43.8%). H NMR (400 MHz,
DMSO-d6) δ 8.82 (dd, J = 6.5, 1.4 Hz, 1H), 8.49 (dd,
J = 8.7, 1.5 Hz, 1H), 8.38 (t, J = 7.6 Hz, 1H), 7.93 (d,
J = 15.6 Hz, 1H), 7.77 (t, J = 7.6 Hz, 1H), 7.70–7.61 (m,
2H), 7.37 (d, J = 15.6 Hz, 1H), 7.06 (d, J = 8.3 Hz, 2H),
6.83–6.69 (m, 4H), 5.16 (t, J = 4.9 Hz, 2H), 4.43 (t,
J = 4.9 Hz, 2H), 3.05 (s, 6H), 2.20 (s, 3H). Anal. Calcd.
For C24H27N2BrO: C, 65.59%, H, 6.21%, N, 6.38% found:
C, 66.41%, H, 6.25%, N, 6.51%.
In order to obtain the inclusive information of
1
1
For 1c (red solid, yield 38.7%). H NMR (400 MHz,
VD⊂CB[7], the H NMR spectra of VD and VD⊂CB[7]
DMSO-d6) δ 9.06 (d, J = 6.1 Hz, 1H), 8.54 (d, J = 8.3 Hz,
1H), 8.38 (d, J = 7.9 Hz, 1H), 8.06–7.95 (m, 2H), 7.83 (d,
J = 7.7 Hz, 2H), 7.77 (d, J = 8.8 Hz, 2H), 7.57 (d,
J = 15.6 Hz, 1H), 7.47 (t, J = 9.1 Hz, 2H), 7.39 (t,
J = 7.9 Hz, 1H), 7.25 (t, J = 7.5 Hz, 1H), 6.98 (d,
J = 7.6 Hz, 1H), 6.80 (d, J = 8.8 Hz, 2H), 5.45–5.33 (m,
2H), 4.64 (d, J = 4.5 Hz, 2H), 3.05 (s, 6H). Anal. Calcd. For
C27H27N2BrO: C, 68.20%, H, 5.74%, N, 5.89% found: C,
68.96%, H, 5.79%, N, 6.03%.
(VD in the presence of 1.0 equiv of CB[7]) in D2O at pD
2 were recorded.
Compared with pure 1a, the protons H5, H6, H7 and
H8 of DMPE on 1a⊂CB[7] are observed to obviously shift
to the higher field (ΔδH5 = −0.45 ppm, ΔδH6 = −0.45
ppm, ΔδH7 = −0.45 ppm, ΔδH8 = −0.25 ppm, and ΔδH12,
ΔδH13, ΔδH14 are close to zero) (as shown in Figure 2).
We can also found that the protons H5, H6, H7, H8 of
DMPE on 1b-1d⊂CB[7] shift upfield (ΔδH51b = −0.40

4
Q. GU ET AL.
1
Figure 1. H NMR spectrum (400 MHz, D2O) of 1a (pD = 2) in the presence of 1.0 (a) and 3.0 (b) equiv of CB[7].
1
Figure 2. H NMR spectra (D2O, 400 MHz) of 1a (a), 1a⊂CB[7] (b). Spectra a and b were recorded at pD 2.
ppm, ΔδH61b = −0.37 ppm, ΔδH71b = −0.43 ppm and
ΔδH81b −0.33 ppm; ΔδH51c −0.50 ppm,
ΔδH61c = −0.50 ppm, ΔδH71c = −0.43 ppm and
ΔδH81c −0.45 ppm; ΔδH51d −0.37 ppm,
ΔδH61d = −0.37 ppm, ΔδH71d = −0.43 ppm and
ΔδH81d = −0.25 ppm) and H12-14 of DMPE on 1b⊂CB
[7], H12-18 of DMPE on 1c-1d⊂CB[7] have no shift (as
shown in figure 3–5). However, compared with pure 1e,
the chemical shifts of hydrogen protons of 1e have no
change in the mixture of 1e and CB[7], we can conclude
that there is no inclusion between 1e and CB[7] (as
shown in Figure 6).
=
=
=
=
Fluorescent titration of the 1a-1e⊂CB[7]
Concentration solutions of 1a-1e (1 × 10−5 mol/L) were
titrated by different concentrations (0.1, 0.2, 0.3, 0.4, 0.5,
0.6, 0.7, 0.8, 0.9, 1.0 × 10−5 mol/L) of CB[7] solution, and
fluorescence curves and inclusive constants were
obtained, respectively (figure 7–8).

SUPRAMOLECULAR CHEMISTRY
5
1
Figure 3. H NMR spectra (D2O, 400 MHz) of 1b (a), 1b⊂CB[7] (b). Spectra a and b were recorded at pD 2.
1
Figure 4. H NMR spectra (D2O, 400 MHz) of 1c (a), 1c⊂CB[7] (b). Spectra a and b were recorded at pD 2.
When CB[7] was added, the emission spectrum
blue shifted from 598 to 589 nm, and the fluores-
cence intensity was declined. When the concentra-
tion of CB[7] solution was equal to 1a, fluorescence
intensity decreased to its minimum, with further
addition of CB[7], the fluorescence intensity was
kept unchanged, which proved 1:1 complex
between 1a and CB[7] was constructed. A plot of
1/ΔF (ΔF = F-F0) against 1/CB[7] was drawn to get a
straight line, and the ratio of linear intercept and
slope is the inclusive constant. Where F is the fluor-
escence intensity of different concentrations of CB

6
Q. GU ET AL.
1
Figure 5. H NMR spectra (D2O, 400 MHz) of 1d (a), 1d⊂CB[7] (b). Spectra a and b were recorded at pD 2.
1
Figure 6. H NMR spectra (D2O, 400 MHz) of 1e (a), 1e⊂CB[7] (b). Spectra a and b were recorded at pD 2.

SUPRAMOLECULAR CHEMISTRY
7
Figure 7. Fluorescence titration curves 1a-1e⊂CB[7] (a-e) and inclusive constants of 1a-1e⊂CB[7] (f-j).

8
Q. GU ET AL.
Figure 8. Emission spectra of 1a-1d in the presence of CB[7] titration dot map (a-d).
Figure 9. Mechanism of fluorescence quenching of VD⊂CB[7].
[7] complexing with 1a, and F0 is the fluorescence
intensity of guest solution. The K1a⊂CB[7] was esti-
mated to be 11.172 × 105 L/mol, with the correlation
coefficient of the fitted curve being R2 = 0.96774.
When titrating 1b with CB[7], the emission spectrum
blue shifted from 600 to 594 nm with the increasing con-
centration of CB [7]. K1b⊂CB[7] = 11.149 × 105 L/mol,
R2 = 0.99733.

SUPRAMOLECULAR CHEMISTRY
9
Figure 10. Simulated distance between two arms in 1a-1e.
When titrating 1c with CB[7], the emission spectrum
blue shifted from 600 to 594 nm with the increasing
concentration of CB [7]. K1c⊂CB[7] = 9.676 × 105 L/mol,
R2 = 0.98837.
When titrating 1d with CB[7], the emission spectrum
blue shifted from 600 to 594 nm with the increasing
concentration of CB [7]. K1d⊂CB[7] = 7.825 × 105 L/mol,
R2 = 0.99840.
However, when 1e was titrated with CB[7], fluorescence
titration curve showed the great difference from that of 1a-
1d⊂CB[7], and was almost a horizontal straight line, which
suggested that there is no inclusion between 1e and CB[7].
This phenomenon consists with the above NMR results,
thereby, the inclusive constant could not be obtained.
Fluorescence titration curves of 1a-1d showed that
the fluorescence intensity decreased with the increas-
ing concentration of CB[7], and finally the fluorescence
intensity decreased 2–3 times. Based on this fact, we
supposed that CB[7] was included on the DMPE arm,
which leads to blocked intramolecular charge transfer
(ICT), on the other hand, coplanarity between the ben-
zene ring and pyridine ring was broken due to the
steric exclusion between the included DMPE arm and
AE arm, (Figure 9).
In order to investigate relationship between value of
inclusive constant and width of aryloxy arm, gaussian
density functional theory[B3LYP/6–31 g(d,p)] was used
to evaluate width of aryloxy arm and distance between

10
Q. GU ET AL.
DMPE arm and AE arm in VD (Figure 10). Results
showed that different widths of aryloxy (9-anthryloxy
(7.26 Å) > 2-naphthyloxy (5.08 Å) > 1-naphthyloxy
(4.86 Å) > p-tolyloxy (2.42 Å) > phenyloxy (2.41 Å))
brought about different distances between two arms
(9-anthryloxy (4.08 Å) < 2-naphthyloxy (4.20 Å) < 1-
naphthyloxy (4.61 Å) < p-tolyloxy (6.30 Å) < phenyloxy
(6.41 Å)) due to steric hindrance. Therefore, capacity of
inclusion was 1a> 1b> 1c> 1d> 1e, and consistent with
Complexation. Adv. Mater. 2013, 25, 6864–6867.
DOI:10.1002/adma.201303652.
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Yamagishi, T. Host–Guest Complexation of Perethylated
Pillar[5]Arene with Alkanes in the Crystal State. Angew.
Chem. Int. Ed. 2015, 127, 9987–9990. DOI:10.1002/
ange.201503489.
(6) Strutt, N.L.; Forgan, R.S.; Spruell, J.M.; Botros, Y.Y.;
Stoddart, J.F. Monofunctionalized Pillar[5]Arene as a
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inclusive constants K1a⊂CB[7]
>
K1b⊂CB[7]
>
K1c⊂CB[7]
> K1d⊂CB[7], but 1e did not form the effective inclusion.
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Conclusions
In summary, we synthesized the V-type stilbene dyes
(VD, 1a-1e), in which one arm contains DMPE unit as
conclusive location with CB[7], and kept unchanged;
another arm contains AE unit with different steric hin-
drance, such as phenyloxy (1a), tolyloxy (1b), naphthy-
loxy (1c and 1d) and 9-anthryloxy (1e). By the
fluorescence spectroscopy and 1H NMR investigation,
we found that CB[7] can include 1a-1d, the order of
inclusive constants K1a⊂CB[7]> K1b⊂CB[7]> K1c⊂CB[7]
> K1d⊂CB[7] is consistent with the magnitude of the
steric hindrance, and 1e did not form the inclusion. In
order to further confirm this fact, gaussian density func-
tional theory[B3LYP/6–31 g(d,p)] was used to evaluate
width of aryloxy arm and distance between DMPE arm
and AE arm in VD. Results showed that the capacity of
inclusion was 1a> 1b> 1c> 1d> 1e, which was consistent
with inclusive constants. Therefore, a series of steric hin-
drance controlled [2]pseudorotaxanes were constructed.
Disclosure statement
No potential conflict of interest was reported by the authors.
(14) Yang, Q.; Wang, P.; Zhao, C.; Wang, W.; Yang, J.; Liu, Q.
Light-Switchable Self-Healing Hydrogel Based on Host-
Guest Macro-Crosslinking. Macromol. Rapid. Commun.
2017, 38, 1600741. DOI:10.1002/marc.v38.6.
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