Y. Wei, et al.
ReactiveandFunctionalPolymers144(2019)104351
triethylamine (1.5 ml) were dissolved in 30 ml dry THF under the ni-
trogen atmosphere and stirred in ice/water bath for 30 min.
Methacryloyl chloride (1.35 ml) in 4 ml dry THF was added dropwise
into the above reaction mixture. And then, the solution was kept stir-
ring for 36 h at room temperature. Finally, the solvent THF was eva-
porated under reduced pressure, the residue was dissolved in 60 ml
CH2Cl2 and the organic solution was washed with water for three times.
The crude product was purified by silica gel column chromatography
using ethylacetate/petroleum ether (1/15) as eluent. The white solid
NMR (600 MHz, CDCl3) δ 7.77 (d, 2H), 7.44 (d, 4H), 7.34 (d, 4H), 7.29 (t,
4H), 7.26–7.20 (m, 4H), 7.16 (d, 2H), 6.79 (t, 4H), 6.21 (d, 2H), 3.99–3.88
(m, 4H), 3.45 (t, 4H), 2.11–1.81 (m, 8H). 13C NMR (151 MHz, CDCl3) δ
158.24, 148.98, 145.08, 136.93, 128.49, 128.06, 127.40, 126.88, 125.50,
122.97, 119.49, 118.83, 114.73, 113.92, 82.10, 66.75, 33.45, 29.46, 27.87.
2.2.4. Synthesis of model host molecule H2
In 500 ml flask, the 1,4-dimethoxybenzene (1.105 g, 8 mmol), 0.36 g
paraformaldehyde and 160 ml CH2Cl2 were added. After the mixture
was stirred for 30 min, the solution of trifluoromethanesulfonic acid
(106 μl, 1.2 mmol) in 40 ml CH2Cl2 was slowly added. The reaction
mixture was stirred for further 4 h, the organic reaction solution was
washed with water for three times and dried with anhydrous sodium
sulfate. The purified H2 was obtain by silica gel column chromato-
graphy using ethylacetate/petroleum ether (1:10) as eluent, white
solid, 0.46 g, yield 38.3%. M/z calcd for [M + Na+]+: 773.3302,
found 773.3306. 1H NMR (600 MHz, CDCl3) δ 6.76 (s, 10H), 3.77 (s,
10H), 3.64 (s, 30H). 13C NMR (151 MHz, CDCl3) δ 150.80, 128.26,
114.06, 55.78, 29.65.
product was obtained, 0.54 g, yield 43.2%. M/z calcd for [M + H]+
:
279.1089, found 279.1129. 1H NMR (400 MHz, DMSO) δ (ppm): 12.83
(s, 1H), 8.11 (s, 2H), 7.68–7.37 (m, 2H), 7.18 (d, 4H), 6.21 (s, 1H), 5.83
(s, 1H), 1.92 (s, 3H). 13C NMR (151 MHz, DMSO) δ (ppm):165.64,
152.20, 151.02, 135.65, 128.54, 128.34, 128.19, 122.95, 18.51.
Synthesis of pillar[5]arene monomer M2: In 1000 ml flask, the 2-(4-
methoxyphenoxy)ethyl acrylate (P2, 0.44 g, 2 mmol), 1,4-dimethox-
ybenzene (4.42 g, 32 mmol), FeCl3 (0.82 g, 5 mmol) and 640 ml CH2Cl2
were added. After the mixture was stirred for 30 min, the 2.88 g par-
aformaldehyde was added. The reaction mixture was further stirred
under nitrogen atmosphere at 30 °C for 4 h. After filtration, the organic
solution was wash with water and then dried with anhydrous sodium
sulfate. The pure white solid product was obtained by silica gel column
chromatography using ethylacetate/petroleum ether (1/9) as eluent,
0.42 g, yield, 32.4%. M/z calcd for [M + Na]+: 857.3516, found
857.4277. 1H NMR (500 MHz, CDCl3): δ 6.80–6.75 (m, 10H), 6.20 (d,
1H), 5.94 (q, 1H), 5.62 (d, 1H), 4.43 (s, 1H), 4.05 (s, 1H), 3.82–3.75 (m,
10H), 3.70–3.60 (m, 27H). 13C NMR (125 MHz, CDCl3) δ: 150.81,
150.75, 131.09, 128.42, 128.28, 128.22, 128.11, 127.89, 115.77,
114.26, 114.15, 114.04, 66.89, 63.33, 55.95, 55.81, 55.77, 55.74,
55.72, 55.67, 29.84, 29.68, 29.61, 29.47.
3. Results and discussion
3.1. Design and preparation of supramolecular system
Pillar[5]arene is widely used as host in supramolecular host-guest
recognition and benzimidazole unit is a fluorophore with high quantum
efficiency. They were combined in one copolymer and used in this
paper as a polymeric fluorescence host. The absorbance bands of
naphthalimide and naphthopyran overlapped with the emission band to
a large extent, therefore, they can quench the fluorescent emission of
benzimidazole through energy transfer when they are close near via the
host-guest recognition as guests. In addition, the open-form of naph-
thopyran will increase the spectra overlap and further increase the
fluorescence quenching extent of benzimidazole. Naphthopyran pos-
sessed good photochromic reversibility under UV light and visible light
or heat, so it is anticipated that photochromic reaction of naphthopyran
can reversibly modulate the fluorescence emission of benzimidazole at
a certain extent. All the molecular structure of designed compounds and
polymer were well characterized with 1H NMR, 13C NMR, mass spec-
trometer and GPC methods.
Synthesis of polymeric host H1: M1 (0.3405 g, 0.4 mmol), M2
(0.1113 g, 0.4 mmol) and 4 ml 1,4-dioxane were added into 10 ml flask.
After stirred 20 min, catalyst 2,2-azobisisobutyronitrite (AIBN,
0.0016 g) was added. The reaction mixture was degassed with nitrogen
by three freeze-pump-thaw cycles and stirred at 65 °C for 16 h. After the
mixture was colded down to room temperature, the copolymer was
precipitated into methanol for three times and dried in a vacuum at
room temperature. The copolymeric host H1 was obtained as white
powder (0.21 g, yield: 46.5%; Mn,GPC = 67,428, Mw /Mn = 2.7975).
The molar ration of M1 to M2 in the H1 molecule was calculated to be
1:2 according to the integral area of two protons on benzene ring
nearby imidazole unit of M1 and four protons of ethyl of M2.
3.2. Study on the recognition of pillar[5]arene (host) and N-butyl bromide
(guest)
2.2.2. Synthesis of guest G1
The mixture of G1-b (1.56 g,5 mmol),carbon tetrabromide (3.3 g,
10 mmol) and triphenylphosphine (2.62 g, 10 mmol) in 30 ml CH2Cl2
was stirred at room temperature for 24 h. The reaction solution was
washed with water for three times and then dried with anhydrous so-
dium sulfate. The product was purified by the silica gel column chro-
matography using ethylacetate/petroleum ether (1/3) as eluent, saffron
solid, 0.89 g, yield 47.6%. M/z calcd for [M + Na++2H]+: 399.0684,
found 399.0503. 1H NMR (600 MHz, CDCl3) δ 8.57 (dd, 1H), 8.48 (d,
1H), 7.66 (dd, 1H), 7.12 (d, 1H), 4.24–4.19 (m, 2H), 3.47 (t, 2H), 3.11
(s, 6H), 1.94 (ddd, 4H). 13C NMR (151 MHz, CDCl3) δ 164.23, 157.18,
132.88, 131.41, 131.25, 125.43, 125.05, 123.14, 113.47, 44.93, 39.27,
33.42, 30.45, 27.09.
The molecular recognition behavior of pillar[5]arene and N-butyl
bromide was studied by 1H NMR titration in CDCl3 solutions using host
model compound H2 and guest G2 as representatives. The 1H NMR
spectra (Fig. 1a) of G2 showed different patterns in its own solution and
alkyl protons H1, H2, H3 and H4 of n-butane in the mixed solution are
shifted remarkedly to upfield than that in its own solution. On the
contrary, the peaks for phenyl protons in mixed solution did not present
obvious shift. This result indicated that guest G2 executed the efficient
recognition with host H2 via the complexation of n-butyl bromide with
Further investigation of the complexation ratio of H2 with G2 was
carried out with Job's plot. A series of solutions containing G1 and H2
in CDCl3 were prepared and the sum of concentration of H2 and G2 in
each solution remained constant at 5 mM but their molar ration varied.
Their 1H NMR spectra were measured after mixing them for 15 s. Job's
plot was drawn by plotting the chemical shift change of alkyl proton H4
against the mole fraction of guest G2, shown as Fig. 1b. The maximum
guest complex was formed.
2.2.3. Synthesis of photochromic naphthopyran guest G2
1-(4-(4-bromobutoxy)phenyl)-1-phenylprop-2-yn-1-ol (4 g, 11 mmol),
2,6-dihydroxy naphthalene (0.8 g, 5 mmol) and p-toluenesulfonic acid
(0.1 g) were dissolved in 20 ml CH2Cl2. The mixture was stirred under ni-
trogen atmosphere at room temperature for 48 h, and then the organic so-
lution was washed with water and dried with anhydrous sodium sulfate.
The product was purified by silica gel column chromatography using
ethylacetate/petroleum ether (5/1) as eluent, saffron solid, 3.4 g, yield
36.8%. M/z calcd for [M + Na + 2H]+: 865.1484, found 865.1298. 1H
In order to study the binding relationship between the pillar[5]
arene and G2, 1H NMR titration experiments were carried out with a
3