Cucurbit[7]uril-tetraphenylethene host-guest system induced emission activity

Article abstract of DOI:10.1039/c5ra24264a

A host-guest complex was successfully constructed from cucurbit[7]uril (Q[7]) and quaternary ammonium-modified tetraphenylethene derivative, 1,1,2,2-tetrakis{2-[2-(N,N,N-trimethylammonium)ethyoxyl]phenyl}-tetraphenylethene bromide (TAPET), and characteriz

Full text of DOI:10.1039/c5ra24264a

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Cucurbit[7]uril–tetraphenylethene host–guest
system induced emission activity†
Cite this: RSC Adv., 2016, 6, 4478
Rong Jiang, Shuang Wang and Jinping Li*
A host–guest complex was successfully constructed from cucurbit[7]uril (Q[7]) and quaternary ammonium-
modified tetraphenylethene derivative, 1,1,2,2-tetrakis{2-[2-(N,N,N-trimethylammonium)ethyoxyl]phenyl}-
tetraphenylethene bromide (TAPET), and characterized by a wide range of techniques. This host–guest
complex exhibits an AIE nature, resulting in strong fluorescence in dilute solution due to the restriction
of the intramolecular rotation of the phenyl moieties of TAPET upon the addition of Q[7]. Moreover,
addition of competitive guest 1-adamantanamine hydrochloride (Ada) leads to effective dissociation of
the host–guest complex Q[7]–TATPE and turns the fluorescence emission off.
Received 17th November 2015
Accepted 24th December 2015
DOI: 10.1039/c5ra24264a
www.rsc.org/advances
Molecular compounds with aggregation-induced emission phenyl moieties of TPE were included in the cavity of b-cyclo-
1
2
(
AIE) or aggregation induced enhanced emission (AIEE)
dextrins through host–guest interaction, the neutral TPE
7
b
characteristics have provided a promising platform for the derivative then showed an enhanced uorescence emission.
design and creation of efficient light emitters ranging from Also in 2014, Li reported the self-assembled uorescent organic
3
optical materials to sensors. Since the rst AIE molecular nanoparticles fabricated from p-sulfonatocalix[4]arene and
1
a
8f
compound reported by Tang et al. in 2001, a wide variety of AIE quaternary ammonium-modied TPE in water. Recently,
molecular materials have been synthesized based on the Huang and co-workers constructed a host–guest inclusion
3b,4a
mechanism of restricting the intramolecular motions (RIM).
complex from water-soluble pillar[6]arene and tetraphenyle-
Among various AIE molecular compounds, tetraphenylethene thene derivative, which exhibited strong uorescence in dilute
8h
(TPE) and its functionalized derivatives can be readily obtained solution.
9
via facile synthetic transformation, and are non-emissive in the
Cucurbit[n]urils (Q[n]), as a new class of macrocyclic hosts,
molecularly dissolved state but show enhanced uorescence exhibit exceptional molecular recognition properties due to their
4
emission in both the aggregated form and the solid state. In high binding affinities and tunable association and dissociation
contrast to the conventional organic luminophores with properties and have been widely utilized in developing supramo-
aggregation-caused quenching (ACQ) effect, TPE derivatives lecular switches, supramolecular polymers, supramolecular
with AIE-activity have demonstrated improved efficiency and nanoparticles, andothersupramolecular systemswithfascinating
10
sensitivity as chemosensors, bio-probes, and solid-state emit- properties and application potentials. However, there still exists
5
ters with great application potentials.
no AIE-active supramolecular system that is constructed between
Actually many methodologies including increasing the cucurbit[n]uril and TPE derivative depending on the host–guest
solvent viscosity, lowering the temperature, and applying high interactions, to the best of our knowledge. Herein we describe the
1
b,6
pressure
have been developed to fabricate TPE-based AIE- construction of the cucurbit[7]uril (Q[7])-based host–guest system
1b,4b
active materials.
In particular, host–guest recognition was with 1,1,2,2-tetrakis{2-[2-(N,N,N-trimethylammonium)ethyoxyl]-
proved efficient to restrict the intramolecular motions of TPE phenyl}-tetraphenylethene bromide (TAPET), Scheme 1, repre-
molecules in recently years, resulting in the turn-on of uores- senting the rst Q[n]-involved host–guest complex constructed
7
cence emission of TPE derivatives via the AIE mechanism.
with TPE. In particular, in this host–guest system the phenyl
Quite a number of macrocyclic hosts such as crown ethers, moieties of TAPET were included in the cavity of Q[7], resulting in
calixarenes, cyclodextrins, and pillararenes have been employed thestrongemissionofTAPETindilutesolution. Thepresentresult
to include the TPE molecule inside their cavities to induce the therefore represents the rst host–guest system constructed
8
in AIE-activity. In 2014, Tang demonstrated that when the between cucurbit[n]uril and TPE with AIE-activity.
9a
HostQ[7]waspreparedaccordingtothepublishedprocedure.
The target guest together with corresponding intermediary
Research Institute of Special Chemicals, Taiyuan University of Technology, Taiyuan, compounds was synthesized in a facile route as shown in Scheme
0
30024, China. E-mail: jpli211@hotmail.com
S1 (ESI†). At the very beginning, the intermediate compound tet-
rahydroxyl TPE (1) was synthesized by McMurry coupling reaction
between two bis(4-hydroxyphenyl)-methanones. Then reaction of
†
Electronic supplementary information (ESI) available: Synthesis procedure,
NMR, MALDI-TOF mass spectrum, electronic absorption and uorescence
spectra, DLS and AFM results. See DOI: 10.1039/c5ra24264a
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Scheme 1 Schematic representation of the formation of the AIE-
active host–guest complex between Q[7] and 1,1,2,2-tetrakis{2-[2-
(
N,N,N-trimethylammonium)ethyoxyl]phenyl}-tetraphenylethene
bromide (TAPET).
1
Fig. 1 H NMR spectra of TATPE (A) as well as Q[7] and TATPE in the
2 3
tetrahydroxyl TPE with 1,2-dibromoethane promoted by K CO
molar ratio of 2 : 1 (B), 2.5 : 1 (C), 3 : 1 (D), 3.5 : 1 (E), 4 : 1 (F), and Q[7]
andKIinDMFledtotheformationofcompound1,1,2,2-tetrakis[4-
ꢀ
(G) recorded in D
2
O at 25 C.
8g,h
(
2-bromoethoxy)phenyl]ethane (2), which further reacted with
trimethylamine in ethanol afforded the target guest compound
TATPE(3).Itisworthnotingthatthequaternaryammoniumcation
moieties incorporated in this guest compound lend this
compound good water-solubility, rendering the reaction with
watersolubleQ[7]tobeabletooccurinaqueoussolution.Bysimply
mixing Q[7] and TATPE in aqueous solution, strong host–guest
interactions between the two species of molecules led to the
formationofpseudorotaxaneQ[7]–TATPE.Allthekeyintermediate
1
13
andtargetcompoundshavebeencharacterizedby Hand CNMR
spectroscopy, Fig. S1 and S2 (ESI†).
In order to investigate the complexation of Q[7] with TATPE
1
in solution, H NMR titration experiments were rst performed
by adding increasing amount of Q[7] into the solution of TATPE
in D O. As clearly shown in Fig. 1, the proton H and H
2 1 2
attributed to the methyl proton and methylene proton experi-
ence signicantly upeld shi from 3.09 and 3.66 ppm to 2.88
and 3.48 ppm, respectively. Furthermore, the methylene
protons H
3 4
and aromatic protons H exhibit obviously down-

eld shi from 4.31 and 6.69 ppm to 4.39 and 6.83 ppm,
respectively. These shis in their direction and magnitude
ꢀ
2
Fig. 2 ITC data for the binding of Q[7] with TATPE in H O at 25 C.
suggest that the methyl group and methylene linked with the
+
quaternised N of the guest TATPE are located within the inte-
rior cavity of Q[7] due to the formation of the inclusion complex
Q[7]–TATPE. This is further conrmed by the NOESY cross- binding stoichiometry of Q[7] to TATPE is 4 : 1. This is also in
signals between the methyl proton H1 of TATPE and the accordance with the MALDI-TOF mass spectroscopic result,
methylene proton of Q[7] in the NOESY spectrum of the mixture Fig. S4 (ESI†). In addition, the association constant of K
a
¼ (3.06
5
ꢃ4
2
between TATPE and Q[7] in D O, Fig. S3 (ESI†).
ꢁ 0.16) ꢂ 10 M for Q[7] with TATPE was also derived on the
Isothermal titration calorimetry (ITC) measurements are basis of corresponding experimental result. Such a high
able to afford quantitative information for the host–guest binding constant suggests the relatively strong host–guest
complexation including both the binding affinity and thermo- interaction between Q[7] and TATPE, indicating the formation
dynamic origin. As a consequence, a solution of TATPE was of stable inclusion complex in aqueous solution. Meanwhile,
ꢀ
consecutively injected into the solution of Q[7] at 25 C to record the relatively large negative enthalpy value of Q[7]–TATPE
the exothermic binding isotherm, Fig. 2, resulting in the reso- system deduced reveals that the assembly process of inclusion
lution of the binding molar ratio value of N ¼ 0.243. This result complex of Q[7] with TATPE is typically driven by a favorable
is very close to the expected value of 0.25, suggesting the enthalpy change, Table S1 (ESI†).
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1
As described above, both H NMR and ITC measurements a host–guest supramolecular complex with amphiphilicity
indicate the formation of pseudorotaxane unit between Q[7] depending on the electrostatic interactions between the
and TATPE in aqueous solvent, which might be able to inhibit quaternary ammonium groups of TATPE and oxygen atoms at
the intramolecular rotation of the phenyl moieties of TATPE, the portals of Q[7]. With the Q[7]–TATPE host–guest system as
inducing TATPE to exhibit strong emission. As a consequence, starting material, further self-assembly depending on the p–p
the uorescence properties of 2.0 mM TATPE in the absence or interactions between the phenyl moieties of neighboring TATPE
presence of Q[7] in water were comparatively investigated. As in the host–guest system, with the help of the C–H/p inter-
shown in Fig. 3, TATPE is nearly nonemissive in water due to the actions between the methylene group of Q[7] and the phenyl
efficient nonradiative annihilation process induced by the moieties of TATPE in neighboring host–guest system, results in
intramolecular rotation of phenyl moieties of TATPE. However, the formation of spherical-like nano-structures.
upon addition of Q[7], the rotation of phenyl moieties of TATPE
Due to the stronger binding ability of Q[7] with 1-ada-
11
is restricted, leading to the remarkably increased uorescence mantanamine hydrochloride (Ada), Ada was added into the Q
intensity. The emission intensity gradually got increased along [7]–TATPE system as a competitive guest. As shown in Fig. S7
with the increase in the Q[7] added, which became nearly (ESI†), upon adding Ada into the Q[7]–TATPE supramolecular
constant when 140.0 mM Q[7] was added, resulting in the complex in D
observation of approximately 16-fold uorescence enhance- obviously upeld shis, with H
2
O, all of the proton resonances of Ada exhibited
, HII, and HIII having chemical
I
ment. In addition, such a Q[7]-induced signicant uorescence shi differences of 0.63, 0.61 and 0.67 ppm in comparison with
enhancement of TATPE is even to be clearly observed by naked the free guest Ada. At the same time, all the signals of TATPE in
eye: When TATPE was excited at 365 nm using a UV lamp in the the complex Q[7]–TATPE system returned to the original state of
presence of 35.0 equiv. of Q[7], a strong cyan uorescence the free TATPE molecule, indicating the dissociation of the
appeared. This gives additional support for the AIE mechanism original supramolecular system Q[7]–TATPE and concomitant
as proposed.
formation of a new inclusion complex between Q[7] and Ada.
As expected, along with the addition of increasing amount of
Further investigation of the binding stoichiometry between
Q[7] and TATPE was carried out by Job's plot method. As shown competitive guest Ada into the Q[7]–TATPE system at a xed
ꢃ6
in Fig. S5 (ESI†), the maximum peak appeared at the molar concentration of 2.0 ꢂ 10 M in H
2
O, the uorescence inten-
fraction of 0.20, corresponding to 1 : 4 binding stoichiometry of sity got gradually decreased at 464 nm while the emission
TATPE to Q[7]. This is consistent with that deduced from the signicantly increased at 396 nm, Fig. 4 and S8 (ESI†), with
ITC analysis as detailed above.
a clear isoemissive point appearing at 420 nm, indicating the
Furthermore, transmission electron microscopy (TEM) was dissociation of the Q[7]–TATPE complex and the formation of
used to provide further insight into the size and morphology of a new complex between Ada and Q[7]. These results reveal that
the supramolecular aggregates formed from Q[7] and TATPE. in the presence of Ada, TATPE slipped out of the cavity of Q[7]
Aer evaporating the solution of Q[7] and TATPE on copper and Ada was included by Q[7]. The underlying optical change
grid, spherical micelles with a diameter of ꢄ40 nm were was ascribed to the formation of a more stable complex Q[7]–
observed by TEM image, and the spherical micelles showed Ada. This results in the nonemissive TATPE molecules again in
multilamellar stacks, Fig. S6 (ESI†). Most probably, self-
assembly between Q[7] and TATPE led to the formation of
ꢃ6
ꢃ1
Fig. 3 Fluorescence spectra of TATPE (2 ꢂ 10
addition of Q[7] at 470 nm in H
mol L ) upon Fig. 4 Fluorescence spectra of a solution of TATPE (2.0 mM) and Q[7]
ꢀ
2
O with excitation of 330 nm (the (70.0 mM) upon addition of Ada in H
2
O at 25 C with excitation of 330
TATPE/Q[7] molar ratio changing from 0 to 35). The inset photographs nm (the Ada/Q[7] molar ratio changing from 0 to 38). The inset
show the corresponding fluorescence change (left: 2.0 mM TATPE; photographs show the corresponding fluorescence change (left: 2.0
right: 2.0 mM TATPE and 70.0 mM Q[7]) illuminated at 365 nm using mM TATPE and 70.0 mM Q[7]; right: 2.0 mM TATPE, 70.0 mM Q[7], and
ꢀ
ꢀ
a UV lamp at 25 C.
70.0 mM Ada) illuminated at 365 nm using a UV lamp at 25 C.
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solution. Moreover, the uorescence change yielded by the carbonate (0.14 g, 1.0 mmol), compound 1 (0.20 g, 0.50 mmol)
addition of Ada could also be visualized by the naked eye under in dry DMF (100.0 mL) together with 1,2-dibromoethane (3.7 g,
ꢀ
a 365 nm lamp, Fig. 4.
20.0 mmol) was added at 50 C. The reaction mixture was stirred
In summary, an AIE-active host–guest system was success- for 48 h. Aer the solid was ltered off, the solvent was removed
fully constructed between Q[7] and quaternary ammonium- under reduced pressure. The residue was puried by ash
2 2
modied tetraphenylethene derivative TATPE, representing column chromatography on silica gel using CH Cl as eluent to
1
the rst example of AIE-active host–guest complex formed afford 0.35 g of product as a purple solid, 85%. H NMR (400
ꢀ
between Q[7] and TATPE. This host–guest complex exhibits AIE MHz, DMSO-d
6
, 25 C) d (ppm): 6.87 (d, J ¼ 8.0 Hz, 8H), 6.72 (d, J
nature, resulting in strong uorescence in dilute solution due to ¼ 8.0 Hz, 8H), 4.23 (t, J ¼ 12.0 Hz, 8H), 3.75 (t, J ¼ 12.0 Hz, 8H).
the restriction of the intramolecular rotation of the phenyl Preparation of 1,1,2,2-tetrakis{2-[2-(N,N,N-trimethylammonium)-
moieties of TAPET upon the addition of Q[7]. Moreover, addi- ethyoxyl]phenyl}-tetraphenylethene bromide (3). Compound 2 (0.25
tion of competitive guest 1-adamantanamine hydrochloride g, 0.30 mmol) and trimethylamine (33% in ethanol, 6.50 mL, 25.1
leads to effective dissociation of the host–guest complex Q[7]– mmol) were added to ethanol (50.0 mL). The solution was reuxed
TATPE and turns the uorescence emission off. The present overnight. Then the solvent was removed by evaporation and
result is helpful for the future design and construction of host– deionized water (20.0 mL) was added. Aer ltration, a clear solu-
guest systems with AIE activity with application potentials.
tion was obtained. Then water was removed by evaporation. The
residue was washed thoroughly with diethyl ether, giving the water
soluble product 3 with the yield of 0.28 g, 88%. H NMR (400 MHz,
1
Experimental section
General remarks
ꢀ
D O, 25 C) d (ppm): 6.96 (d, J ¼ 8.0 Hz, 8H), 6.69 (d, J ¼ 8.0 Hz, 8H),
2
4
.31 (t, J ¼ 12.0 Hz, 8H), 3.66 (t, J ¼ 12.0 Hz, 8H), 3.10 (s, 36H). MS
All reagents and solvents were obtained from commercial calcd for C60 Br
H
58
N
4
O
4
4
: 1218.74; found: m/z 1219.53. Anal. calcd
sources without further purication. The compounds of 1–3 for C46H N O Br : C, 52.09; H, 6.46; N, 5.28; found C, 53.14; H,
68 4 4 4
8g,12
were prepared according to the literature procedure.
6.38; N, 5.19.
Measurements
Notes and references
1
H NMR spectra were recorded on a Bruker DPX 400 spec-
O and DMSO-d . Steady-state uorescence spec-
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6
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0
00 000
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ꢀ
4
(1.7 mL, 15.0 mmol) was
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ꢀ
and quenched with 10% K
ted with CH Cl . The organic layer was collected and concen-
trated. The residue was puried by ash column
chromatography on silica gel using n-hexane/CH Cl
/acetone ¼
0 : 5 : 1 as eluent, affording 0.31 g of target compound as
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2
2
2
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6 Y. Hong, J. W. Y. Lam and B. Z. Tang, Chem. Commun., 2009,
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ꢀ
a white solid, 31%. H NMR (400 MHz, DMSO-d , 25 C) d (ppm):
6
8
.93 (s, 4H), 7.06 (d, 8H), 6.47 (d, 8H).
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