DOI: 10.1002/chem.201602635
Communication
&
Smart Materials
Macroscopic Responsive Liquid Quantum Dots Constructed via
Pillar[5]arene-Based Host-Guest Interactions
Junkai Ma, Fangdan Shi, Demei Tian, and Haibing Li *[a]
fluorescent-film sensors are largely unexplored and pose a big
Abstract: Liquid quantum dots (QDs) have been used as
challenge.[15]
a fluorescent films sensor. Constructing a macroscopic, re-
To address this challenge, herein we present a new strategy
sponsive, liquid QD system for lysine (Lys) is a challenging
to construct liquid QDs using host–guest interactions. Pillarar-
task. To achieve a selective macroscopic response towards
enes are a relatively new class of supramolecular host that
Lys, herein we present a new strategy for integrating
have received considerable attention because of their novel
host–guest chemistry into a liquid QD system. Water-solu-
symmetrical, pillar-shaped architectures, unique host–guest
ble pillar[5]arene WP5 was designed and synthesized as
properties, electron-rich cavities and highly tunable functionali-
a host. WP5 was introduced onto the surface of PEG1810-
ty.[16] Based on these unique properties, pillararenes can be
modified QDs by host–guest interactions to obtain liquid
used as building blocks to construct supramolecular architec-
WP5-1810-QDs. The interaction between WP5 and Lys is
tures including rotaxane,[17] pseudorotaxanes,[18] and polyrot-
stronger than that between WP5 and PEG-1810, causing
axanes.[19] Such adjustability allow pillararenes to display specif-
WP5 to be released from the 1810-QDs surface in the
ic responses to different kinds of analytes, such as alkanes,[20]
presence of Lys, resulting in macroscopic fluorescence
azobenzenes,[21] and viologen derivatives.[22] Thus, pillararenes
quenching. This smart material shows promise in amino
have been incorporated into various nanomaterials, such as Ag
acid sensing and separation.
and Au nanoparticles, which have potential applications in
chemical and biological sensors.[23,24]
Amino acids are the building blocks of proteins, play vital
Quantum dots (QDs),[1] with unique photophysical properties
and size-controlled fluorescence, have attracted broad interest
over the past few decades and have been widely used in appli-
cations such as optical sensors,[2] optoelectronics[3] and biologi-
cal imaging.[4] However, QDs are usually synthesized in solvents
that are constraining for applications in many fields. Mean-
while, solid-state QDs are subject to fluorescence quenching.
To solve these problems, novel, solvent-free QDs, denoted as
liquid QDs, were recently developed.[5–9] A variety of ap-
proaches to prepare liquid QDs have been proposed. For in-
stance, Giannelis and coworkers prepared liquid ZnO[10] and
PbS[11] QDs by ionic exchanges, but the fluorescent properties
of the resultant QDs were undesirable. Xiong et al. used a clas-
sic extraction method to produce liquid CdSe QDs with excel-
lent fluorescent properties.[12] More recently, we synthesized
multi-emission liquid CdSe QDs based on a hydrogen-bonded
assembly.[13] The resulting hydrophobic, liquid QDs displayed
tunable optical and structural properties, and could be used as
fluorescent-film sensors.[14] As far as we know, liquid QD-based
roles in the metabolic processes of living bodies.[25] In particu-
lar, lysine (Lys) is important in protein synthesis, and human
growth. A major post-translational modification that plays an
important regulatory role in almost every aspect of both eu-
karyotic and prokaryotic cells involves Lys.[26] Consequently, se-
lective recognition of Lys is crucial in biochemistry and medical
science. Designing a selective receptor for Lys and immobiliz-
ing this receptor into a liquid QDs system are the two main
objectives of this work. To achieve high selectivity for Lys, the
carboxyl group was used because it can interact with amino
acids via intermolecular hydrogen bonds. The electron-rich
cavity of pillar[5]arene can bind amino acids.[27] Herein, we
design and synthesize a water-soluble pillar[5]arene modified
with carboxylic acid groups (WP5) by a “thiol-ene” click reac-
tion[28] (Figure 1A). WP5 was introduced onto the surface of
1810-QDs by host–guest interaction and construct a macro-
scopic Lys responsive liquid QDs system.
First, WP5 was synthesized by the classical “thiol-ene” click
reaction (Figure 1A). The structure of WP5 was confirmed by
1H and 13C NMR spectroscopy and mass spectrometry (Sup-
porting Information, Figures S1–11). The host–guest interaction
[a] J. Ma, F. Shi, Prof. D. Tian, Prof. H. Li
Key Laboratory of Pesticide and Chemical Biology (CCNU)
Ministry of Education, College of Chemistry
Central China Normal University
1
of WP5 and Lys was then investigated by H NMR spectrosco-
py. As shown in Figure 1B, when 1.0 equivalent of Lys was
added to a solution of WP5, H1 of Lys exhibited an upfield shift
of d1 =0.05 ppm, and the Ha aromatic protons, Hb of WP5 shift-
ed downfield by da =0.28 ppm, db =0.12 ppm because of in-
clusion-induced deshielding effects and hydrophobic interac-
tions. These changes are consistent with the alkyl chain of Lys
being inserted into the cavity of WP5 to form a host–guest
Wuhan 430079 (P.R. China)
Supporting Information containing experimental and characterization de-
tails (fluorescence spectroscopy, TEM, UV/Vis, IR, contact-angle measure-
Chem. Eur. J. 2016, 22, 13805 –13809
13805
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