base stimuli whereas the “silent” mode of the system could be regulated by the
oxidation/reduction reaction of ferrocene unit. This study laid a solid foundation
for the fabrication of advanced logic circuits with memories or sequential
functions.
Most of the molecular machines with switchable fluorescent output were studied
in the solution phase, which limited their practical applications. Therefore, Qu et al.
[15] introduced the above bistable [2]rotaxane system into SiO 2 nanoparticles
because of their chemical stability and optically transparent features (Fig. 2b).
Intriguingly, the fluorescence intensity could be reversibly modulated by the acid/
base stimuli in the solid state of the SiO 2 nanoparticles as well as in the solution state,
thus paving a bright avenue for the construction of smart stimuli-responsive surfaces
with tunable functions. Subsequently, they grafted the [2]rotaxane system into a
polymer chain again and successfully constructed a fluorescent switch based on a
polyrotaxane system, further expanding the application fields of solid-state fluorescent sensors (Fig. 2c) [16].
White-light-emitting devices have drawn wide attention in recent years, and
these devices are now being considered to be a promising solid-state lighting
source [17]. Tian and coworkers [18] reported a bistable [2]rotaxane with orthogonally tunable multicolor fluorescence features including white-light emission via
combining a rotaxane-type molecular switch and traditional fluorescent switch
(Fig. 3). A blue-light-emitting [2]rotaxane was constructed by N-propyl-1,8naphthalimide (PNA) as the stopper and two Fc electron donor-decorated
DB24C8 as the molecule shuttle. With the increase of base, the blue fluorescence
intensity of the [2]rotaxane was continuously strengthened due to the weakened
PET process between Fc unit and PNA group, accompanied by the decrease of
yellow fluorescence intensity of the perylene bisimide derivative (PBI) owing to
the aggregation of PBI molecule. Therefore, the emission color, containing whitelight emission, could be reversibly regulated by simply changing pH. These
systems provided a reliable method for the construction of multicomponent tunable
fluorescence molecular systems.
Mechanochemistry, activated by mechanical force instead of conventional
stimuli (i.e., pH, light, and heat), has been widely studied in the past few years.
However, the conventional mechanophores activated by cleaving covalent bonds
required a relatively high activation energy, and the process was usually irreversible [19]. Therefore, a linear polyurethane containing the rotaxane-based supramolecular mechanoluminophore with reversible on/off switching of its
photoluminescence properties was reported by Weder and coworkers [20]. As
shown in Fig. 4, the [2]rotaxane was fabricated via a 4,7-bis(phenylethynyl)-2,1,3benzothiadiazole (BTH)-decorated 1,5-dinaphtho[38]crown-10 cycle and an electronpoor 1,4,5,8-naphthalenetetracarboxylic diimide (NpI) motif. Tri(p-tert-butylphenyl)
phenylmethane stoppers were introduced into the system to lock in the structure. The
free crown ether cycle could emit bright fluorescence, while the solution of [2]
rotaxane showed no emission because the fluorescence of the BTH unit was
quenched by the NpI moiety. Then, the [2]rotaxane was grafted into polymer chains
through the reaction of two hydroxyl groups sites modified on the cycle and the
110
Y. Zhou et al.
oxidation/reduction reaction of ferrocene unit. This study laid a solid foundation
for the fabrication of advanced logic circuits with memories or sequential
functions.
Most of the molecular machines with switchable fluorescent output were studied
in the solution phase, which limited their practical applications. Therefore, Qu et al.
[15] introduced the above bistable [2]rotaxane system into SiO 2 nanoparticles
because of their chemical stability and optically transparent features (Fig. 2b).
Intriguingly, the fluorescence intensity could be reversibly modulated by the acid/
base stimuli in the solid state of the SiO 2 nanoparticles as well as in the solution state,
thus paving a bright avenue for the construction of smart stimuli-responsive surfaces
with tunable functions. Subsequently, they grafted the [2]rotaxane system into a
polymer chain again and successfully constructed a fluorescent switch based on a
polyrotaxane system, further expanding the application fields of solid-state fluorescent sensors (Fig. 2c) [16].
White-light-emitting devices have drawn wide attention in recent years, and
these devices are now being considered to be a promising solid-state lighting
source [17]. Tian and coworkers [18] reported a bistable [2]rotaxane with orthogonally tunable multicolor fluorescence features including white-light emission via
combining a rotaxane-type molecular switch and traditional fluorescent switch
(Fig. 3). A blue-light-emitting [2]rotaxane was constructed by N-propyl-1,8naphthalimide (PNA) as the stopper and two Fc electron donor-decorated
DB24C8 as the molecule shuttle. With the increase of base, the blue fluorescence
intensity of the [2]rotaxane was continuously strengthened due to the weakened
PET process between Fc unit and PNA group, accompanied by the decrease of
yellow fluorescence intensity of the perylene bisimide derivative (PBI) owing to
the aggregation of PBI molecule. Therefore, the emission color, containing whitelight emission, could be reversibly regulated by simply changing pH. These
systems provided a reliable method for the construction of multicomponent tunable
fluorescence molecular systems.
Mechanochemistry, activated by mechanical force instead of conventional
stimuli (i.e., pH, light, and heat), has been widely studied in the past few years.
However, the conventional mechanophores activated by cleaving covalent bonds
required a relatively high activation energy, and the process was usually irreversible [19]. Therefore, a linear polyurethane containing the rotaxane-based supramolecular mechanoluminophore with reversible on/off switching of its
photoluminescence properties was reported by Weder and coworkers [20]. As
shown in Fig. 4, the [2]rotaxane was fabricated via a 4,7-bis(phenylethynyl)-2,1,3benzothiadiazole (BTH)-decorated 1,5-dinaphtho[38]crown-10 cycle and an electronpoor 1,4,5,8-naphthalenetetracarboxylic diimide (NpI) motif. Tri(p-tert-butylphenyl)
phenylmethane stoppers were introduced into the system to lock in the structure. The
free crown ether cycle could emit bright fluorescence, while the solution of [2]
rotaxane showed no emission because the fluorescence of the BTH unit was
quenched by the NpI moiety. Then, the [2]rotaxane was grafted into polymer chains
through the reaction of two hydroxyl groups sites modified on the cycle and the
110
Y. Zhou et al.