Controlling Supramolecular Chirality of Two-Component Hydrogels by J

Helical or chiral nanostructures in nature, such as the right-handed B-form double helix of DNA and the triple helix of collagen, could provide critic...
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Article Cite This: J. Am. Chem. Soc. 2018, 140, 6467−6473

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Controlling Supramolecular Chirality of Two-Component Hydrogels by J- and H‑Aggregation of Building Blocks Guofeng Liu,†,∥ Jianhui Sheng,†,‡,∥ Hongwei Wu,† Chaolong Yang,† Guangbao Yang,† Yongxin Li,† Rakesh Ganguly,† Liangliang Zhu,*,‡ and Yanli Zhao*,†,§ †

Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, 637371, Singapore ‡ State Key Laboratory of Molecular Engineering of Polymers, Department of Macromolecular Science, Fudan University, Shanghai 200433, P.R. China § School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798, Singapore S Supporting Information *

ABSTRACT: While manipulating the helicity of nanostructures is a challenging task, it attracts great research interest on account of its crucial role in better understanding the formation mechanisms of helical systems. For the supramolecular chirality in self-assembly systems, one challenge is how to understand the origin of supramolecular chirality and inherent helicity information on nanostructures regulated by functionality-oriented stacking modes (such as J- and Haggregation) of building blocks. Herein, two-component hydrogels were prepared by phenylalanine-based enantiomers and achiral bis(pyridinyl) derivatives, where helical nanofibers with inverse handedness as well as controllable helical pitch and diameter were readily obtained through stoichiometric coassembly of these building blocks. The helix inversion was achieved by the transition between the J- and H-aggregation of bis(pyridinyl) derivatives, which was collectively confirmed by circular dichroism, scanning electron microscopy, Fourier transform infrared spectroscopy, and single X-ray crystallography. Interestingly, the helical coassemblies with opposite handedness could be obtained not only from the enantiomeric building blocks but also from the chiral monomers with the same configurational chirality by exchanging achiral additives. This work provides insight into the origin and helicity inversion of supramolecular chirality in molecular self-assembly systems and may shine light on the precise fabrication of chiral nanostructures for potential applications in smart display devices, optoelectronics, and biological systems.

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INTRODUCTION Helical or chiral nanostructures in nature, such as the righthanded B-form double helix of DNA and the triple helix of collagen, could provide critical functions and are known to endow special characteristics to life.1 By mimicking nature chiral nanostructures, artificial chiral nanostructures have displayed potential applications in chemistry,2 materials science,3−6 and biological systems.7,8 To construct chiral nanostructures, small molecular self-assembly is an efficient and extensively used strategy, since the building blocks could self-organize in a controllable pathway through noncovalent interactions including hydrogen bonding, halogen bonding, π−π stacking, van der Waals, and electrostatic interactions.8−16 Usually, helical and twisted nanostructures are easily aggregated from corresponding chiral building blocks; hence, the supramolecular chirality of nanostructures is highly dependent on the inherent molecular chirality of building blocks.17−20 On the other hand, chiral nanostructures could also be established from nonchiral building blocks under the induction of asymmetric stimuli including stirring modes, circularly polarized light, and chiral additives.21−23 A few studies have achieved regulation on © 2018 American Chemical Society

the supramolecular chirality of nanostructures by nonchiral factors, such as pH, light, temperature, achiral solvent, and additives.24−27 The reason is that the participation of chiral factors or nonchiral stimulus could greatly affect the stacking arrangement of building blocks and the chiral conformation of obtained assemblies.28,29 Since the stacking arrangement of building blocks plays a crucial role in the supramolecular chirality of assemblies, confirming functionality-oriented stacking modes (i.e., J- and H-aggregation) of building blocks would be highly helpful to predict the handedness of resulted nanostructures during the self-assembly process. As the J- and H-aggregation of πconjugated molecules could influence the photochemistry and photophysics of supramolecular materials, they have been frequently employed in the construction of organic photovoltaics30,31 and photoelectronics.32−38 For example, lightemitting properties of organic luminophores could be successfully tailored by the supramolecular chirality of Received: March 26, 2018 Published: May 7, 2018 6467

DOI: 10.1021/jacs.8b03309 J. Am. Chem. Soc. 2018, 140, 6467−6473

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Journal of the American Chemical Society

Figure 1. Schematic presentation of the helical inversion triggered by H-aggregation of DPDS and J-aggregation of EDPAz in the coassembly process with (left) LCHF or (right) DCHF. M represents left-handed helical nanofibers, and P represents right-handed helical nanofibers.

assemblies.3 However, no detailed mechanisms could predict exact supramolecular chirality and helicity inversion of assemblies to date, although a variety of interesting results and phenomena with different handedness have been reported.24,39−45 The reasons are that it is unpredictable to (1) facilely tune the supramolecular chirality of nanostructures through the exchange of J- and H-aggregation of building blocks and (2) revert their handedness and chiroptical activity in supramolecular hydrogel systems. Two-component supramolecular hydrogels, based on the self-assembly (coassembly) of building blocks with diverse chemical structures and physical functions orthogonally integrating at the molecular scale and synergistically organizing into supramolecular aggregates, offer a facile way to tailor the properties of the gels and endow supramolecular assemblies with switchable stimulus-responsiveness.46 In addition, the supramolecular chirality of gels could be precisely regulated by molecular chirality and spatial arrangement of programmable building blocks.16 Hence, two-component supramolecular gels are an ideal testbed for better understanding the mysteries of supramolecular chirality through the J- and H-aggregation of building blocks in the coassembled systems. Herein, phenylalanine-appended 1,4-cyclohexyl-dicarboxamide enantiomers (D/LCHF, whereas D represents D-phenylalanine isomer and L stands for L-phenylalanine isomer) were rationally designed to coassemble with equimolar bis(pyridinyl) derivatives (i.e., 4,4′-dipyridyl disulfide (DPDS) and 4,4′azopyridine (EDPAz)) for the construction of helical nanostructures with controllable handedness (Figure 1). The achiral DPDS and EDPAz are employed as guest linkers, which not only coassemble with LCHF or DCHF by cooperative intermolecular hydrogen bonding interactions but also endow the redox and light responsiveness of resulted hydrogels.24,46,47 After systematic studies, it was unexpectedly found that uniform helical nanofibers with opposite handedness were obtained from the coassembly of LCHF+DPDS (righthandedness, P-helicity) and LCHF+EDPAz (left-handedness, M-helicity), on account of the H-aggregation induced by DPDS and the J-aggregation triggered by EDPAz during the coassembly process. A counterpart result was also shown in the D-type gelators, where DCHF+DPDS assemble into Mhelical nanofibers and DCHF+EDPAz organize into P-helical nanostructures.

from Sigma-Aldrich and used without further purification. Selfstanding hydrogels were readily obtained by heating an equimolar mixture of phenylalanine-based enantiomers and bis(pyridinyl) derivatives in aqueous solution followed by standing at room temperature (Figure S1). The nanofibrous structures of coassembled hydrogels were systematically investigated by scanning electron microscopy (SEM). The equimolar mixture of LCHF and DPDS (LCHF+DPDS) leads to purely right-handed (P-type) helical nanofibers (Figure 2a),

Figure 2. SEM images of (a) LCHF+DPDS with P-helical nanofibers, (b) DCHF+DPDS with M-helical nanofibers, (c) LCHF+EDPAz with M-helical nanofibers, and (d) DCHF+EDPAz with P-helical nanofibers. (e) Pitch and (f) diameter of these helical nanofibers obtained from hydrogels with different handedness (cyan, P-helicity; pink, Mhelicity).

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whereas the equimolar mixture of DCHF and DPDS (DCHF +DPDS) presents helical nanofibers with M-helicity (Figure 2b). Interestingly, as compared with the P-helicity in LCHF +DPDS, LCHF and equimolar EDPAz (LCHF+EDPAz) synergistically organize into fully opposite M-helical nanofibers, while DCHF+EDPAz aggregate into P-type chiral ones (Figure

RESULTS AND DISCUSSION Controllable Handedness of Helical Nanostructures in Hydrogels. DCHF and LCHF were synthesized according to previous reports,16 and DPDS and EDPAz were purchased 6468

DOI: 10.1021/jacs.8b03309 J. Am. Chem. Soc. 2018, 140, 6467−6473

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Journal of the American Chemical Society

Figure 3. CD and UV−vis spectra of (a) D/LCHF+DPDS and (b) D/LCHF+EDPAz hydrogels obtained using a 0.1 mm quartz cuvette with the total gelator concentration at 2.0 mg/mL. Temperature-dependent CD and UV−vis spectral changes of (c) LCHF+DPDS and (d) LCHF+EDPAz hydrogels with 5 °C intervals (total concentration of 2.15 × 10−3 M, molar ratio of 1:1).

2c,d). These results suggest that helical coassemblies with opposite handedness could be not only obtained from the enantiomeric building blocks but also achieved from the chiral monomers with the same configurational chirality by exchanging achiral additives (DPDS and EDPAz). In addition, the helical pitch and diameter of these chiral nanostructures were well investigated. For CHF-based hydrogel systems, the helical pitch of D/LCHF+DPDS is in the range 128−152 nm, which is less than the pitch of helical fibers that fell in the 174−196 nm range in D/LCHF+EDPAz hydrogels (Figure 2e). Furthermore, the diameter of 28−48 nm for D/ LCHF+DPDS nanostructures is much smaller than that of D/ LCHF+EDPAz around 52 nm (Figure 2f). The results imply that both the helical pitch and diameter of coassemblies are closely related to the achiral bis(pyridinyl) derivatives used. Different helical pitch and diameter in these nanofibers may be ascribed to the compact stacking of DPDS-based hydrogels and relatively loose packing in EDPAz-based hydrogel systems. Chiroptical Activity of Coassembled Hydrogels. In order to further explore the fascinating helical coassembly, circular dichroism (CD) spectra of the obtained systems were recorded in detail. Since the UV−vis absorption of major chromophores is largely overlapped during the coassembly process, the CD spectrum was employed to reveal the helical stacking modes of the coassembled systems. For the DCHF +DPDS hydrogel, the CD spectrum exhibits negative peaks at 210 and 290 nm, while the mirror-imaged CD spectrum of the LCHF+DPDS hydrogel shows positive CD absorption at ∼210 and 290 nm (Figure 3a). According to the molecular CD spectra of D/LCHF depicted in Figure S2, the positive CD signal of LCHF+DPDS hydrogel around 210 nm is assigned to the chiral stacking of L-type phenylalanine chromophore and

the positive Cotton effect at 290 nm is ascribed to the induced supramolecular chirality of DPDS in P-type helical aggregates after being coassembled with LCHF. When comparing the LCHF+DPDS coassembled hydrogel with the self-assembled LCHF hydrogel, an obvious blue-shift from 218 to 210 nm was displayed in the inset of Figure 3a. More interestingly, the CD spectrum of the DCHF+EDPAz hydrogel in Figure 3b reveals strongly positive CD absorption at 238 and 358 nm assigned to the UV absorption peaks of DCHF at 220 nm and EDPAz at 286 nm, respectively, while the CD spectrum of LCHF+EDPAz displays a mirror-imaged curve with negative CD absorptions at 238 and 358 nm. In comparison with the negative Cotton effect of DCHF+DPDS in the 210−400 nm range, the DCHF +EDPAz hydrogel displays fully opposite positive CD absorption within 210−400 nm. This observation is consistent with the opposite handedness from SEM measurements. The DCHF+EDPAz hydrogel shows a positive CD signal around 238 nm on account of the helical stacking of the phenylalanine chromophore, which presents a remarkable red-shift as compared with the positive Cotton effect of self-assembled LCHF at 218 nm (the inset of Figure 3b). Comparing the molecular CD signal of LCHF at 219 nm (Figure S3), the CD signal of the LCHF+DPDS hydrogel exhibits a slightly blueshifted positive Cotton effect at 210 nm and the LCHF +EDPAz hydrogel shows an obviously red-shifted negative Cotton effect at 238 nm. These spectral shifts clearly indicate that the H-aggregation of phenylalanine chromophores occurs in LCHF+DPDS, while the J-aggregation of phenylalanine chromophores takes place in LCHF+EDPAz. Thus, the chiroptical activity inversion of the coassembled hydrogels between LCHF+DPDS and LCHF+EDPAZ mainly results 6469

DOI: 10.1021/jacs.8b03309 J. Am. Chem. Soc. 2018, 140, 6467−6473

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Journal of the American Chemical Society

Figure 4. (a) Anisotropy factor g values of CD spectra at 353 nm for coassembled hydrogels with varying molar ratios of LCHF to EDPAz (LCHF:EDPAz = 1:2, 1:1, 5:4, 2:1, and 5:1). (b) FT-IR spectra of LCHF+EDPAz, LCHF+DPDS, LCHF xerogel, EDPAz, and DPDS. (c) Packing structure in the single crystal of EDPAz stabilized by hydrogen bonding interactions. (d) Packing structure in the single crystal of DPDS driven by π−π stacking interactions. Schematic representation for (e) loose J-type packing of LCHF+EDPAz induced left-handed coassembly and (f) compact H-type stacking of LCHF+DPDS induced right-handed coassembly. The dashed lines in parts e and f represent the intermolecular hydrogen bonding interactions.

in the gel−sol coexisting system. After further heating, the g value reduced rapidly and the molecular chirality of LCHF was mainly observed. For the LCHF+EDPAz sample depicted in Figure 3c, the decreasing intensity of the negative CD peak at ∼294 nm was weakened when the temperature was increased over 45 °C (Figure S4b), suggesting the transition of the gel-tosol phase. Significantly, the negative CD peak at 219 nm decreased upon increasing the temperature to 45 °C and fully inverted into a positive CD signal after additional heating (Figures 3d and S4b), revealing the transformation of the chirality with the reversal of CD signals. As compared with the remaining positive CD absorption around 219 nm in the LCHF +DPDS system, the inversion of the chirality in the LCHF +EDPAz system during the gel-to-sol process clearly indicates the supramolecular chirality inversion between LCHF+EDPAz and LCHF+DPDS (Figure 2a,c). In comparison with the UV absorption maximum of the EDPAz molecule that appeared at 282 nm, the CD absorption maximum of the LCHF+EDPAz gel at 20 °C locates at 294 nm. This slight red-shift indicates a medium J-aggregation of EDPAz in the coassembly of LCHF +EDPAz. The anisotropy factor g values at 219 and 294 nm in Figure 3d clearly illustrate the disassociation of the coassembly and the transmission of chiral information between the supramolecular level and molecular scale triggered by heating.

from the H- and J-aggregation of phenylalanine chromophores during the coassembly process. Dynamic Chirality Transition from Supramolecular Level to Molecular Scale. To gain further insight into the Hand J-aggregation induced helicity inversion in these coassembled hydrogels, dynamic CD spectra of hydrogels based on LCHF were measured under the gelator concentration at 1.0 mg mL−1. The CD spectrum of LCHF+DPDS at 20 °C shows positive CD absorption peaks around 220 and 285 nm in the spectral region of achiral aromatic units in DPDS (Figure 3c), suggesting the construction of a helical conformation. After heating up to 70 °C, the positive CD peak at 285 nm gradually decreases and simultaneously redshifts to 293 nm, until completely disappearing under further heating. The LCHF+DPDS system at 90 °C reveals positive CD absorption at around 220 nm but CD silence at around 290 nm, suggesting the disassociation of helical coassemblies. More interestingly, the red-shift of the maximum CD signal from 285 to 293 nm corroborates the H-aggregation of DPDS in the LCHF+DPDS hydrogel. In addition, the anisotropy factor g value at 285 nm was summarized as a function of heating temperature in Figure S4. When the LCHF+DPDS system was treated below 75 °C, the g value remained more than 1.0 × 10−4, indicating that the supramolecular chirality was dominant 6470

DOI: 10.1021/jacs.8b03309 J. Am. Chem. Soc. 2018, 140, 6467−6473

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Journal of the American Chemical Society The supramolecular chirality was dominant below 60 °C, and the molecular chirality of LCHF was mainly shown upon further heating (Figure S4d). Thus, the interconversion of molecular chirality and supramolecular chirality could be reversibly tuned by changing the medium temperature on account of the association and disassociation of coassemblies mainly driven by hydrogen bonding interactions. In addition, it could be reasonably speculated that the H-aggregation of DPDS and J-aggregation of EDPAz are the major driving forces inducing the H- and Jaggregation of phenylalanine chromophores in the coassemblies of LCHF+DPDS and LCHF+EDPAz, respectively, finally resulting in inverse chiroptical activity and handedness of coassembled hydrogels. Exploring the Mechanism and Stoichiometry of Chiral Coassembly. To investigate the underlying mechanism and stoichiometry of coassembly based on phenylalanine enantiomers and bis(pyridinyl) derivatives, the CD and UV−vis spectra of coassembled hydrogels based on LCHF and EDPAz with different molar ratios (LCHF/EDPAz = 1:2, 1:1, 5:4, 2:1, and 5:1) were investigated in detail (Figure S5). For the molar ratio of 1:2 (LCHF+2EDPAz), the weakly positive Cotton effect at ∼208 nm was similar to that in the molecular CD spectrum (Figure S2a), indicating that the positive CD signal could be assigned to the molecular chirality of LCHF. This conclusion was further demonstrated by the CD silence around 275 nm as compared with the strong UV absorption of EDPAz (Figure S5). In contrast, coassembled hydrogels with molar ratios of LCHF to EDPAz at 1:1, 5:4, 2:1, and 5:1 show remarkable negative CD effects at ∼225 nm and 325−350 nm, ascribed to the UV absorption of phenylalanine and EDPAz, respectively (Figure S5). The anisotropy factor g value at 353 nm was summarized as a function of the molar ratio of LCHF to EDPAz (Figure 4a), which clearly illustrates that the preferred stoichiometry of the coassembly between LCHF and EDPAz is 1:1. The reasons are that the LCHF molecule could self-assemble into infinite assemblies for the formation of nanofibrous gels when insufficient EDPAz is used. On the other hand, excess EDPAz would induce the formation of discontinuous coassemblies on account of strong hydrogen bonding interactions between pyridinyl and carboxylic acid groups. Hence, remarkable supramolecular chirality from the helical packing of EDPAz is induced by the coassembly of LCHF and EDPAz with a rational molar ratio. As a control, EDPAz shows CD silence in aqueous solution (Figure S6). The results were further confirmed by gel tests illustrated in Figures 4a and S7. Fourier transform infrared spectroscopy (FT-IR) was employed to (1) explore the helical inversion and mechanisms of these coassembled hydrogels and (2) obtain insight about the interactions of these coassemblies at the molecular scale.16 When compared with the LCHF hydrogel presenting the carboxylic acid band (νCO of COOH) at 1738 cm−1, the carboxylic acid band of the LCHF+EDPAZ hydrogel was shown around 1731 cm−1 with an obvious decrease, and a new weak peak around 1948 cm−1 (Figures 4b and S8) assigned to the O−H stretching vibration resulted from the hydrogen bonding interaction newly formed between carboxylic acid and pyridinyl units. The strong hydrogen bonding interaction was further demonstrated by the 1H NMR spectra illustrated in Figure S9, where the proton signal assigned to the carboxylic acid group of LCHF was broadened and weakened greatly upon adding the DMSO-d6 solution of EDPAz. Moreover, the

FT-IR spectrum of the LCHF+EDPAz gel clearly displays welldefined amide I and II bands around 1644 and 1542 cm−1 (Figure 4b), demonstrating the participation of the amide units in hydrogen bonding interactions. Interestingly, for the LCHF +DPDS gel, in addition to the new peak located around 1947 cm−1 due to the O−H stretching vibration as well as amide I and II bands around 1645 and 1542 cm−1, an observable peak around 1700 cm−1 is assigned to the hydrogen bonding interaction between carboxyl and amide groups (see the orange region in Figure 4b). This observation indicates that the amide provides double hydrogen bonding with a carboxylic acid group in the coassembly of LCHF+DPDS. Thus, DPDS and EDPAz could lead to distinct aggregation modes of LCHF in the coassembly, which might be assigned to different stacking structures of DPDS and EDPAz during the coassembly process. To further confirm the stacking modes of DPDS and EDPAz in the coassembled hydrogels, single crystals of EDPAz and DPDS were obtained. It should be noted that the cocrystals could not be obtained probably due to the flexibility of LCHF and the competitiveness between gelation and crystallinity. One EDPAz molecule and two water molecules were observed in the single crystal unit cell of EDPAz (Figure S10). The crystal packing structure of EDPAz in Figure 4c clearly shows the absence of π−π stacking interactions, since the adjacent EDPAz molecules are packed in a staggered manner with two kinds of intermolecular hydrogen bonding interactions (Figures 4c, S11, and S12). One type of hydrogen bonding interaction is formed between nitrogen of pyridine and hydrogen of water (N···H− O−H: bond length of 2.822 Å, dihedral angle of 160.10°). The other one is the hydrogen bonding interaction between oxygen of water and hydrogen of another water (H−O···H−O−H: bond length of 2.759 Å, dihedral angle of 166.79°). In the case of the DPDS single crystal, typical crystal stacking of DPDS demonstrates strong interlayer π−π stacking interactions with a distance of 3.330 Å between the nitrogen atom and adjacent plane of the heteroaromatic ring (Figures 4d and S13−S15). The results suggest that DPDS easily adopts H-aggregation, while EDPAz is packed in J-aggregation with a staggered arrangement during the coassembly with LCHF. This conclusion was further consolidated by powder X-ray diffraction patterns, where no characteristic band was observed around 25.4° for EDPAz (Figure S16). However, the powder X-ray diffraction of DPDS shows a remarkable peak at 25.48° assigned to the characteristic π−π stacking interaction.46 It should be noted that both xerogels of LCHF+DPDS and LCHF+EDPAz show no obvious peak around 25.4° on account of weak crystallinity in the gel state. On the basis of these sound results, a mechanism of the coassembly was proposed in Figure 4e,f. For LCHF+EDPAz, strong hydrogen bonding interactions are first constructed between the pyridyl nitrogen atom and the HO unit of a carboxylic acid, driving the building blocks to coassemble in a head-to-tail mode (see the pink region in Figure 4e). Then, a fiber network is formed through the hydrogen bonding interactions between amide units (see the purple region in Figure 4e), inducing the monomer stacking in a staggered arrangement. These two kinds of associated hydrogen bonding interactions collectively stabilize the network of the coassembly, guide the building blocks to pack in a J-type manner, and organize into an M-helix (Figure 4e).46 Thanks to the strong π−π stacking interactions formed in DPDS and the double hydrogen bonding interactions depicted in the orange region of 6471

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absorption at 276 nm was finally increased 1.5 times after UV radiation for 240 min (Figure S19b).

Figure 4f, LCHF+DPDS could stack into a compact H-type arrangement and finally form a right-handed helical coassembly. Supramolecular Chirality of Coassembled Hydrogels Controlled by Glutathione and UV Light. Since DPDS contains a disulfide linkage and EDPAz possesses an azo group, glutathione (GSH) and UV-responsive properties of L-type coassembled hydrogels were investigated spectroscopically by CD/UV absorption techniques, respectively. The CD spectrum of the LCHF+DPDS hydrogel shows an obvious Cotton effect at ∼290 nm (assigned to the helical arrangement of DPDS) after the helical nanofiber formation and gelation in water. The CD intensity was gradually decreased on account of the consumption of DPDS after adding GSH solution, and the CD signal became silent after incubation for 2 h (Figure 5a). The

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CONCLUSION In summary, chiral fibrous structures with handedness inversion as well as controllable pitch and diameter have been successfully fabricated by the coassembly of phenylalaninebased enantiomers and achiral bis(pyridinyl) derivatives through the cooperative hydrogen bonding interactions. The helicity inversion herein is significantly triggered by the H- and J-aggregation of building blocks, two fundamental stacking modes for precisely regulating electronic properties of organic materials. The exploration of this strategy has been collectively demonstrated by SEM, CD, FTIR, and crystallography and further confirmed by dynamic CD investigations regulated by GSH solution and UV light irradiation. The present work not only provides valuable insight on the control of supramolecular chirality but also shines a light on the precise fabrication of chiral supramolecular nanosystems. It may find applications in the amplification and modulation of chirality in dynamic soft matter and functional nanomaterials.

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EXPERIMENTAL SECTION

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ASSOCIATED CONTENT

Preparation of Hydrogels. The DCHF+DPDS hydrogel (0.2 wt % DCHF+DPDS) was taken as a representative to present the preparation process. Equimolar DCHF and DPDS (total concentration: 2.0 mg/mL) were put in a glass vial, and the obtained system was heated to form a homogeneous solution. After standing at room temperature, the solution was solidified into the hydrogel. Crystal Growth of EDPAz and DPDS. In a typical experimental procedure, EDPAz and DPDS were dissolved respectively in acetone/ H2O with a molar ratio of 1:1. Slow evaporation of acetone led to needle-shaped crystals suitable for single crystal determination.

Figure 5. Time-dependent changes in the CD and UV−vis spectra of (a, b) LCHF+DPDS hydrogel after adding 3.0 equiv of GSH aqueous solution and (c, d) LCHF+EDPAz hydrogel under UV irradiation at 365 nm.

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/jacs.8b03309. Experimental procedures, supplemental figures, and single crystal details (PDF) X-ray data for DPDS (CIF) X-ray data for EDPAz (CIF)

results were corroborated by UV experiments, where the intensity of absorption at 275 nm gradually decreased and the UV signal at 323 nm enhanced sharply upon the addition of GSH (Figures 5b, S17, and S18). Interestingly, an obvious redshift (from 290 to 310 nm) was observed after adding GSH solution for 35 min, once again demonstrating the Haggregation of DPDS in the coassembly. Thus, the supramolecular chirality of such coassembled hydrogel is not only regulated by GSH but also highly dependent on the Haggregation of DPDS. On the other hand, the UV light responsiveness of the LCHF +EDPAz hydrogel was also investigated. The CD spectrum of LCHF+EDPAz shows obvious negative Cotton effects at 293 and 222 nm before the radiation under UV light at 365 nm (Figure 5c). Compared with the molecular UV absorption of EDPAz at 282 nm and LCHF at 210 nm, red-shifts occur in LCHF+EDPAz. More interestingly, a slight blue-shift from 293 to 285 nm was observed accompanied by the gradual decrease of the CD intensity at 293 and 222 nm due to the disassociation of the hydrogel induced by the photoisomerization of EDPAz under the irradiation of 365 nm light. The blueshift of the LCHF+EDPAz hydrogel was consistent with the Jaggregation of EDPAz in the coassembly stated above. The CD signal became nearly chirality silenced after exposure to 365 nm light for 240 min, which was further confirmed by the simultaneous UV absorption spectra in Figure 5d, where a blue-shift from 280 to 276 nm was present and the intensity of

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AUTHOR INFORMATION

Corresponding Authors

*[email protected] *[email protected] ORCID

Guofeng Liu: 0000-0003-1911-8546 Liangliang Zhu: 0000-0001-6268-3351 Yanli Zhao: 0000-0002-9231-8360 Author Contributions ∥

G.L., J.S.: These authors contributed equally to this work.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This research is supported by the Singapore Academic Research Fund (Nos. RG121/16, RG11/17, and RG114/17) and the Singapore National Research Foundation Investigatorship (No. NRF-NRFI2018-03). It is partially supported by the National Natural Science Foundation of China (No. 21628401). 6472

DOI: 10.1021/jacs.8b03309 J. Am. Chem. Soc. 2018, 140, 6467−6473

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DOI: 10.1021/jacs.8b03309 J. Am. Chem. Soc. 2018, 140, 6467−6473