which showed potential application in the chemical sensors, drug delivery systems,
or other smart materials.
13.3.1 Chemical Sensors
Fluorescent sensors have attracted attention for both analytical sensing and optical
imaging because of their high sensitivity, fast response time, and technical simplicity
[28]. Once the analyte is recognized by the receptor, the fluorescence signal
can be observed in the form of quenching, enhancement, or shift in the fluorescence
maxima due to either electron transfer, charge transfer, or energy transfer processes.
This allows on-site and real-time detection in an uncomplicated and inexpensive
manner, providing qualitative and quantitative information.
Wang and coworkers reported a pillar[5]arene-modified conjugated host polymer (M1), using the polyphenylacetylene as the backbone (Fig. 12) [26]. Therefore,
this polymer could form the side-chain supramolecular polymer with noctylpyrazinium cation guest. Due to the strong charge transfer between the guest
molecules and conjugated polymer, the fluorescence was quenched. After the addition
of the halide anion (tetrabutylammonium salts), the fluorescence recovery could be
observed due to the strong ion-pair interaction between n-octylpyrazinium cation and
halide anion. The fluorescence enhancement of this system increased in the order of
I
À
< Br
À
< Cl
À
, and the differences in fluorescence intensity could be easily distinguished by naked eyes under UV light illumination, acting as the halide anion probe.
Wu and coworkers reported a thymine-substituted copillar[5]arene, which could
coordinate with Hg
2+ tightly through a TÀHg
2+
ÀT pairing to produce linear supramolecular polymer (Fig. 13) [29]. Moreover, a tetraphenylethylene (TPE) derivative
was synthesized with a nitrile motif at the end of alkyl chain, which exhibited strong
binding affinity with the pillar[5]arene. The copillar[5]arene and TPE derivative
could only form the host-guest complex, which could not restrict the rotation of TPE
motif, resulting in no fluorescence in the mixture solution. However, the addition of
Hg
2+ would lead to the formation of supramolecular network resulting from both the
coordination interaction and the host-guest interaction, in which fluorescence of TPE
would be on for restriction of TPE motif. Moreover, this system could selectively
bind with Hg
2+ , due to the unique coordination capacity of Hg
2+ toward the thymine
moieties, and shield the interference of other metal ions. Finally, the bonded Hg
2+
could be removed by the addition of S
2À , resulting in the generation of HgS
precipitate, to regenerate the sensor systems.
Lin and coworkers synthesized a bis-naphthalimide functionalized pillar[5]
arene (MP5), in which the naphthalimide group could act as a πÁÁÁπ stacking site for
the formation of linear supramolecular polymer as well as a fluorophore (Fig. 14) [30].
After the formation of the supramolecular polymer, it could further self-assemble into
the stable π-gel, with strong aggregation-induced fluorescence in the cyclohexanol.
Moreover, this supramolecular π-gel could successively sense Fe
3+ as well as efficiently
remove Fe
3+ in water. The addition of Fe
3+ into the gel would destroy the πÁÁÁπ stacking
between the naphthalimide group and form the cationÁÁÁπ interaction, which could also
maintain the structure of gels, while induce the quench in the fluorescence emission.
356
X. Wu et al.
or other smart materials.
13.3.1 Chemical Sensors
Fluorescent sensors have attracted attention for both analytical sensing and optical
imaging because of their high sensitivity, fast response time, and technical simplicity
[28]. Once the analyte is recognized by the receptor, the fluorescence signal
can be observed in the form of quenching, enhancement, or shift in the fluorescence
maxima due to either electron transfer, charge transfer, or energy transfer processes.
This allows on-site and real-time detection in an uncomplicated and inexpensive
manner, providing qualitative and quantitative information.
Wang and coworkers reported a pillar[5]arene-modified conjugated host polymer (M1), using the polyphenylacetylene as the backbone (Fig. 12) [26]. Therefore,
this polymer could form the side-chain supramolecular polymer with noctylpyrazinium cation guest. Due to the strong charge transfer between the guest
molecules and conjugated polymer, the fluorescence was quenched. After the addition
of the halide anion (tetrabutylammonium salts), the fluorescence recovery could be
observed due to the strong ion-pair interaction between n-octylpyrazinium cation and
halide anion. The fluorescence enhancement of this system increased in the order of
I
À
< Br
À
< Cl
À
, and the differences in fluorescence intensity could be easily distinguished by naked eyes under UV light illumination, acting as the halide anion probe.
Wu and coworkers reported a thymine-substituted copillar[5]arene, which could
coordinate with Hg
2+ tightly through a TÀHg
2+
ÀT pairing to produce linear supramolecular polymer (Fig. 13) [29]. Moreover, a tetraphenylethylene (TPE) derivative
was synthesized with a nitrile motif at the end of alkyl chain, which exhibited strong
binding affinity with the pillar[5]arene. The copillar[5]arene and TPE derivative
could only form the host-guest complex, which could not restrict the rotation of TPE
motif, resulting in no fluorescence in the mixture solution. However, the addition of
Hg
2+ would lead to the formation of supramolecular network resulting from both the
coordination interaction and the host-guest interaction, in which fluorescence of TPE
would be on for restriction of TPE motif. Moreover, this system could selectively
bind with Hg
2+ , due to the unique coordination capacity of Hg
2+ toward the thymine
moieties, and shield the interference of other metal ions. Finally, the bonded Hg
2+
could be removed by the addition of S
2À , resulting in the generation of HgS
precipitate, to regenerate the sensor systems.
Lin and coworkers synthesized a bis-naphthalimide functionalized pillar[5]
arene (MP5), in which the naphthalimide group could act as a πÁÁÁπ stacking site for
the formation of linear supramolecular polymer as well as a fluorophore (Fig. 14) [30].
After the formation of the supramolecular polymer, it could further self-assemble into
the stable π-gel, with strong aggregation-induced fluorescence in the cyclohexanol.
Moreover, this supramolecular π-gel could successively sense Fe
3+ as well as efficiently
remove Fe
3+ in water. The addition of Fe
3+ into the gel would destroy the πÁÁÁπ stacking
between the naphthalimide group and form the cationÁÁÁπ interaction, which could also
maintain the structure of gels, while induce the quench in the fluorescence emission.
356
X. Wu et al.