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Fabrication of Helical Nanoribbon Polydiacetylene via Supramolecular Gelation: Circularly Polarized Luminescence and Novel Diagnostic Chiroptical Signals for Sensing Chunfeng Chen, Jie Chen, Tianyu Wang, and Minghua Liu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b10392 • Publication Date (Web): 19 Oct 2016 Downloaded from http://pubs.acs.org on October 23, 2016

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ACS Applied Materials & Interfaces

Fabrication of Helical Nanoribbon Polydiacetylene via Supramolecular Gelation: Circularly Polarized Luminescence and Novel Diagnostic Chiroptical Signals for Sensing Chunfeng Chen,1, 2 Jie Chen1,3 Tianyu Wang, 1 and Minghua Liu1-4 * 1

Beijing National Laboratory for Molecular Science (BNLMS), CAS Key Laboratory of Colloid,

Interface and Chemical Thermodynamics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China. 2

National Center for Nanoscience and Technology, Beijing 100190, P. R. China.

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University of Chinese Academy of Sciences, Beijing 100049, P. R. China.

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Collaborative Innovation Center of Chemical Science and Engineering, Tianjin 300072, P. R.

China. *E-mail: [email protected].

KEYWORDS Helical Nanoribbon, Polydiacetylene, Supramolecular chirality, Chiroptical sensing, Organogel

ACS Paragon Plus Environment

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ABSTRACT

Four kinds of commercially available diacetylene (DA) monomers with different chain length, diacetylene positions were fabricated into the organogels via mixing with a chaperone gelator, an amphiphilic L-histidine ester derivative LHC18 that can help the non-gelator to form gels. Upon photo irradiation with a 254 UV light, the white gels underwent topochemical reaction and turned into red or blue gels, depending on the DA monomer structures.

Through the gel

formation, the molecular chirality of LHC18 can be transferred to the polydiacetylene (PDA) and helical nanoribbon structures were obtained. The blue gels showed a clear response to stimuli such as pH variation, heating, mechanical force and organic solvents, and turned into red gels. Interestingly, the blue gel showed strong supramolecular chirality, which could be turned off or changed into red phase CD signals. Such changes in chiroptical signals depended on the external heating and various organic solvents. In the case of heating, the blue gel changed into red one, which showed both strong CD signals and circularly polarized luminescence. In the case of organic solvents, although all the tested solvents made the blue gel to red, only some of them could keep the CD signals, thus providing additional sensing capacity of the PDA system. So far, the blue-to-red color change and the “fluorescence on” was widely used as colorimetric and fluorogenic diagnostic signals for PDA, here we showed an additional chiroptical diagnostic signal for a more precise sensing by using the helical PDA.

Introduction Polydiacetylene (PDA) is one of the most investigated polymers that obtained by photopolymerization of the aligned monomers. When diacetylene (DA) monomers were orderly


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arranged in a required manner, the well-known topochemical reactions upon UV-irradiation through the 1, 4-addition could happen and provide the colored PDA.1-3 The PDA shows unique colorimetric (blue-to-red) 4-6 and fluorogenic7 (non-fluorescent to fluorescent) features that are widely used as colorimetric sensors for detecting various kinds of chemicals.8-13 In order to obtain the PDA, both the design of the DA monomer and the organization of the monomer unit are very important. For the molecular design, the covalent attachment of the certain headgroup to the DA skeleton is a usual way, while the introduction of the metal ions and the other small molecules to assist the arrangement of DA is also employed.

For the topochemical

polymerization, DA derivatives have been usually fabricated into ordered LB films,14-15 vesicles,16-20 layered materials or nanofibers21-27 and organogels,28-32 which would favor the photoreactions. On the other hand, PDA has a π-conjugated system that related to their color changes. In some cases, the π-conjugated system can be easily tuned to chiral conformation.33-35 Several works have shown that PDA could be fabricated into chiral polymers through the organization at the air/water interface,36 attaching the chiral headgroups,37 or by using the circular polarized light.23 Although these chiral PDA have been fabricated and characterized by the CD spectra as well as the SEM, their applications are still limited to those blue to red phase transition and the corresponding CD spectral changes. No further properties beyond were reported so far. During a series of work on the chiral self-assembly of the π-conjugated molecules, we have found that commercially available DA monomers, as shown in Scheme 1, can be fabricated into helical PDA polymers through the gelation via the assistance of a newly designed chaperon gelator. 38


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Scheme 1. An illustration on the basic points of this work. Compounds used in the work. When the chaperone gelator LHC18 and four diacetylene monomers were mixed separately in mixed DMF and water, they formed gels, which could subsequently undergo polymerization upon UV irradiation. The blue gel is composed of helical nanoribbon structure and show CD signals, which could serve as a diagnostic chiroptical signal for sensing. Upon forming the supramolecular gel and subjecting to polymerization, helical nanoribbon structured PDA can be obtained from some DA monomers. For this chiral nanostructured PDA, besides the conventional blue to red shift and fluorescence on properties, new chiroptical property such as “CD on”,

“CD off” and circularly polarized luminescence (CPL) emerged

upon external stimulus. Such properties can be further used to detect more precise interactions between the chiral PDA and chemicals, as illustrated in Scheme 1. We have found that when PCDA and the chaperone gelator formed a co-gel, the blue PDA gel with chiral nanoribbon structure could be obtained. Such blue gel showed a strong supramolecular chirality, which can be turned off or changed into red phase CD signals, depending on the external heating, mechanical force, pH change and various solvents. During the response to these stimuli, all the blue gels changed into undistinguishable red color. However, the chiroptical signals can further distinguish some of the chemicals, thus providing additional sensing capacity of the PDA system.


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Results Fabrication of PDA with helical nanoribbon structure via supramolecular gelation Four kinds of DA monomers terminated with carboxylic acid group were selected, as shown in Scheme 1. These monomers have different alkyl chain lengths and diacetylene positions to the headgroup, in which two of them are directly connected to the carboxylic acid group, while the other two have 8 methylene spacers. These molecules were selected in order to clarify the effect of the packing of alkyl chains, terminal headgroups on the polymerization. Although the individual DA compounds cannot form gel in any organic solvents, upon mixing with the LHC18, a chaperone gelator that help the other non-gelator to form organogels, in a 1:1 molar ratio, white organogels were formed in mixed DMF/water. The gel was formed through a general heat and cool cycle. The DA dispersion in DMF/water was heated to transparent solution at a higher temperature. After the solution was cooled down to room temperature, the gel was formed, which was verified by an inversed test tube method. That is, after the test tube is inversed, no flow means the formation of the gel. The gel is stable under dark. However, upon UV-irradiations with a 254 nm UV light, the gels turn into red or blue color immediately. It was observed that the color evolution is dependent on the structure of the DA monomers. While the others compound with LHC18 gel formed the red gel, the two-component gel of PCDA/LHC18 formed a blue gel. Figure 1 shows the image from gelation to polymerization and UV-Vis spectral changes of the PCDA/LHC18 gel as a function of irradiation time. Upon irradiations with 2 seconds, a new absorption band appears at 647 nm, which can be assigned to a blue phase of the PDA. Upon further irradiation, the intensity of the band increases. After 8 seconds of irradiation, no significant change of the intensity is observed and the absorption maximum finally stopped at 642 nm. While for the other gels, only red gels were obtained and these red


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gels were generally needed long time irradiation. This indicated that the gelation could really help the polymerization of the DA monomers. However, the alkyl chain length and the diacetylene position could change the polymerization. It seemed that PCDA/LHC18 formed the most ordered assemblies and facilitate the blue polymerization.

Figure 1. UV-Vis spectra of the PCDA/LHC18 gel in DMF/water before and after UV irradiation by UV 254 nm light. Previously, we have clarified that in many cases, the self-assembly of achiral molecules with the chiral molecules could cause the chiral transfer.39 In order to clarify if the above gels showed optical activity, we have further measured the CD spectra of the gels, as shown in Figure 2. It is found that the white gels of various monomers co-assembled with LHC18 have no CD signals due to the lack of absorption in the visible region, while the CD signals were gradually appeared after UV 254 nm irradiation. Interestingly, although the gels showed clear absorption spectra, not all of them showed CD spectra. The PCDA/LHC18 gel showed the positive Cotton effect at 670 nm, negative at 480 nm with a crossover at 562 nm (Figure 2B). This means that the Cotton effect was originated from the blue band in PCDA/LHC18 system. For the HDDB/LHC18 gel, only a positive CD spectrum was observed at 492 nm (Figure 2C). The chirality of HDDB/LHC18 is produced comparing the HDDA/LHC18 (Figure 2A), which shows


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the chirality of PDA can be tuned by changing the position of triple bond of diacetylene acid monomers. The gel HDDA/LHC18 is CD silent although the gels tuned into red color also upon photoirradiation. Meanwhile, the CD of polymerized assemblies HCDA/LHC18 also matches the red phase (Figure 2D). This means that through the gel formation, all the DA monomers were arranged to a topochemical favored arrangement that reaction occurred in these system. However, due to the packing differences, the chirality of LHC18 can be transferred to the PDA or not. In the case of HDDA monomer with shorter alkyl chain, the chirality was not transferred.

Figure 2. CD spectra of polydiacetylene after irradiation by UV light 254 nm: HDDA/LHC18 (A); PCDA/LHC18 (B); HDDB/LHC18 (C); HCDA/LHC18 (D).


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SEM observations The gels are general composed of two phases. In order to further clarify the structures formed in the gels, the gel was fabricated into xerogels and their morphologies were observed by the SEM. Figure 3 shows the SEM pictures for four kinds of xerogels.

One-dimensional

nanostructures are essentially formed. First the nanostructures are quite uniform, indicating that both the DA monomer and the LHC18 formed co-assemblies instead of forming nanostructure separately. Second, depending on the alkyl chain length and the position of diacetylene, the morphologies are slightly different. Twisted or helical nanoribbon structures are observed for PCDA/LHC18, HDDB/LHC18 and HCDA/LHC18 xerogels although some non-twisted nanobelts co-existed. While in the xerogels of HDDA/LHC18 the twist of the nanoribbon was not obvious, the crooking of the 1D nanostructure can be seen. After polymerization, the morphologies did not significantly change. These results indicate that through a simple mixing, both LHC18 and the DA monomers can form co-assembled nanostructures. Due to the chiral nature of the chaperone gelator LHC18, the chirality of LHC18 can be transferred to the coassemblies, leading to the helical nanostructures in some gels. In addition, the polymerization of DA did not cause the significant change of the morphologies, which might be due to the topochemical reaction. It should be noted that the CD signal is not necessarily related to the helical nanostructure. Many fibers or nanobelts showing CD signals do not express as helical or twisted nanostructures.40


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Figure 3. SEM images of the co-gels: HDDA/LHC18 (A1); PCDA/LHC18 (B1); HDDB/LHC18 (C1); HCDA/LHC18 (D1); SEM images of the polymerized co-gels after UV 254 nm irradiation: HDDA/LHC18 (A2); PCDA/LHC18 (B2); HDDB/LHC18 (C2); HCDA/LHC18 (D2). Colorimetric and chiroptical detection using blue gel The polymer backbone of PDAs, comprised of alternating ene-yne groups,41, 42 is responsible for intriguing stress-induced chromic (blue-to-red) transition. Such as, PDA has been extensively investigated as potential chemosensors.43, 44A unique property of the PDA is their colorimetric properties using the blue to red color changes. Our gels have similar properties. Although other


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gels are red, gel PCDA/LHC18 is blue gel. It showed a color change upon different stimulus. We have observed an instant clear color changes when the blue gel meets with many chemicals, pH, temperature and mechanics. In this system, we have found that the system could not only show similar color changes but also uncovered new phenomenon.

Figure 4. Multi-stimulation to red gel from the blue gel by heating, organic solvents, pH and mechanical: scheme of blue gel changed to red gel (A); CD spectra of heated-PDA from the blue to the red (B); the FL images of blue gel and red gel (C); CPL of the in situ polymerized red gel (D); CPL spectra of red gel after heating (E). First, the blue gel showed clear changes to pH, mechanics organic solvent and temperature (Figure 4A). At one glance, all these changes are similar to those of the other PDA system. However, we have found that while PCDA/LHC18 gel showed the blue to red changes, the gel caused by the heating can still keep the CD signals. Figure 4B and Figure S1 showed the CD and UV spectra of the gels after changing to red upon external response. Only the red gel by the heating showed the CD signal, in which the positive Cotton effect shifted from 670 nm to 554


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nm with the same shape. However, the other gel disappeared their CD signals, as show in Figure 4D. This means that many stimuli can destroy the chiral conjugation of the blue phase gel, while the heating can keep the chiral arrangement of the conjugate. More interestingly, only the red gel obtained by the heating show the circular polarized luminescence (CPL)45-48, as shown in Figure 4E. A negative CPL band at around 600 nm is observed, highlighting excited-state supramolecular chirality of these PDA assemblies. So far, emission from the red PDA has been widely reported, here, we report the first time the CPL from the chiral red PDA. In addition, the magnitude of CPL can be evaluated by the luminescence dissymmetry factor (glum). In the present case, the value is estimated to be 0.8 × 10-2, which is quite a large value for the organic polymers or assemblies.47 It should be mentioned that the mechanical force such as rubbing can produce heat. Therefore, it is really difficult to distinguish between true mechanochromism and mechanothermochromism for PDA.49

Interestingly, in our chiral gel, the heating-induced red

gel retained the CD signal, while the rubbing-induced gel eliminated the CD signal. Thus, the CD spectra might be useful to distinguish this slightly different mechanochromism and mechanothermochromism.

Second, the blue gel showed interesting response to cyclodextrin (CyD). When our blue gel dispersed in aqueous solution and met with the α-CyD (33mg/mL), the color changed into red, as shown in Fig.5. Interestingly, when we added the other cyclodextrins such as β- or γ-CyD, the speed to change the color was different, with the α-CyD showing the rapid change in 30 minutes, while the β-CyD or γ-CyD very slow. Meanwhile, when the blue co-assemblies interacted with α-CyD, the CD signal of the gel disappeared also (Figure S2).


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Figure 5 UV-Vis spectra of the blue gel response to α-CyD.

Previously, Kim et al have found that α-CyD could promote a blue-to-purple or blue-to-red color transition through the inclusion of the alkyl side chain by the α-CyD. Our color change is suggested to be due to the similar reason. Since the hydrocarbon chain fits the smaller cavity of α-CD better,50 it is reasonable that the PDA gels changed color faster than with β-CyD and γCyD. Third and most interestingly, the chiral PDA can be used to distinguish the organic solvents.51, 52 Figure 6 and S3 shows the CD spectra of the blue gel after interacting with various organic solvents. All the blue gel turned to red and most of them accompanied with the disappearance of the CD signals. Interestingly, when hexane or methanol was used, the gel turned into purple, the color among red and blue. Interestingly, when we measured the CD spectra of the red or purple gels, it was found that the red gels were CD silent, while the purple gel is CD active, as shown in Figure 6. This means that in some cases, the chirality of the PDA conjugate can be maintained. So far, the detection was only used based on the blue-red color change. Here, we showed that using the chiroptical properties, more sense detection can be performed. This adds new insight into the chiral PDA gels, which is the first report on such case.


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Figure 6. CD spectra of the in situ polymerized PCDA/LHC18 blue gels (blue lines) and those after exposing to solvents (red lines): to THF (red) (A) and to ethanol (red) (B). The CD signals respond to various organic solvents: showing CD signals (red); showing no CD signals (gray) (C). Discussion Based on the above results, a schematic illustration can be proposed for the formation of the chiral assemblies and their unique chiroptical properties, as showed in the Figure 7.


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Figure 7. Illustration on the packing, self-assembly and polymerization of LHC18 and DAs. The DA monomer interacted with the chaperon gelator through both electrostatic and Hbonding interactions, which facilitate the DA to be gelled. During the gel formation, the chirality of LHC18 transferred to DA. Upon polymerization, PDA becomes chiral also. Such PDA shows different chiroptical properties to α-CD, selected organic solvents, heating and pH due to the change of the conjugated backbone, as well as the cut of the chiral transfer route from LHC18 to PDA. See detail in the text.

Although the DA monomers cannot form gels and be polymerized, when they mixed with LHC18, they formed the co-gels, which could be further polymerized. The gel formation was due to the strong interaction of the carboxylic acid with the imidazole of LHC18, which could form the electrostatic as well as the H-bond interactions, as shown in Fig.7. In addition, due to the hydrophobic interactions between long alkyl chains and H-bond between the neighboring molecules, the alkyl chains can align in a multilayered parallel manner. Such strong interactions between the headgroups and the alignments of the alkyl chains facilitated the polymerization. Such interactions between and headgroups and the alignment of the alkyl chains were verified from the FT-IR and XRD measurements of the xerogels, as shown in supporting information


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Figure S4-S5. For various xerogels, the asymmetric and symmetric stretching vibrations of CH2 always appeared at 2920 and 2850 cm-1, respectively, suggesting the highly ordered packing of alkyl chains in the PDA gels.53, 54 In addition, the broad band around 1950-2220 cm-1,55, 56 which should be associated with N—H…O stretching bands of imidazolium carboxylate salts, confirming the interactions between carboxylic acids and the histidine head-groups of LHC18. Moreover, the amide I and II bands of LHC18 could be detected at about 1647 and 1544 cm-1, 57, 58

indicating the strong hydrogen bonding between different LHC18 molecules upon self-

assembly. Meanwhile, The stretching vibration of NH appear at 3330 cm-1, stretching vibration of NH appear at near 3317 cm-1, which also suggest interaction of hydrogen bonding between the amide groups of LHC18. In XRD, basically two sets of patterns can be found, as shown in Figure S6. One is in corresponding to the bilayer of LHC18, as designated as d1 in Figure 7, the other is d2, which is layer distance between DA molecules.

It was found that all the XRD patterns (Fig.S6) had a

layer distance of 3.5-3.6 nm for PCDA/LHC18, HDDA/LHC18 and HCDA/LHC18 xerogels, which is the bilayer distance of LHC18.

The other layer distances changed with the DA

monomer used. An additional longer and shorter distance set of 4.3 nm, 3.1 nm were found for the PCDA/LHC18, HDDA/LHC18 xerogels, respectively. This is just in accordance with the longest and shortest alkyl chains of the monomers. For HCDA/LHC18 xerogels, only one set of pattern was observed, which is due to the fact that the molecular length of LHC18 and HCDA is very close. For HDDB/LHC18 xerogels, the d1 layer distance was shortened to 3.0 nm, which might be due to the inclination of the alkyl chain. Another distance of around 1.9 nm might be the half of the bilayer of HDDB.


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Due to the co-assembly and the well-defined packing, the chirality of LHC18 can be transferred to the co-assemblies. It should be noted that such chiral transfer was related not only the interaction between the headgroups but also to the packing of the alkyl chains. Thus, we observed the supramolecular chirality of the gels composed of PCDA/LHC18, HDDB/LHC18 and HCDA/LHC18. However, in the case of HDDA/LHC18 with the shortest alkyl chain, the chirality was not transferred well, maybe due to the less ordered packing of the alkyl chains.

Furthermore, the packing will also influence the polymerization.

The

PCDA/LHC18 gel was polymerized into blue gels, while the other provided to the red gels since the PCDA has the longest alkyl chain and supposed to pack well. In addition, the supramolecular chirality of the co-assemblies can be expressed at a nanoscale, thus we obtained helical nanoribbons in some system. When external stimulus is applied to the chiral PDA gels, there will undergo double changes, which is different from the conventional PDA gels. One is the similar color change as to conventional PDA gels that the conjugate length may change. The other is the change in chirality, which relied on the cooperative interaction between LHC18 and the PDA. When different stimuli were applied the effects could be different. It is clear that all the stimuli can change the conjugation length of PDA, thus all lead the gel to change into red one. However, the broken of the interaction between LHC18 and PDA is different by varied stimuli. It seems that the heating can strength the interactions between the imidazole and carboxylic acids, thus keeping the chirality of the red gel and further producing the CPL.

Other stimuli usually

destroyed the interactions between them, thus leading to the disappearance of the CD signals. For the solvents, the situation is complicate. Those less polar solvents such as cyclohexane and THF will not destroy the electrostatic and H-bond between the imidazole and carboxylic acid.


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The alcohol can help the H-bond. These solvents can help the chiral transfer from LHC18 to PDA, thus maintaining the CD signals. Other polar solvents or toluene may destroy the electrostatic interactions between imidazole and carboxylic acid or π−π stacking between imidazoles. These solvents will cut the chiral transfer from LHC18 to PDA and lead to the disappearance of the CD signal. CONCLUSIONS In conclusion, the chiral PDA is obtained through the gel formation and some new insight into the chiroptical properties of the gel is found. Although the diacetylene monomers cannot form gels, the co-self-assembly with a chaperon gelator LHC18 lead to the gel formation, which can be subsequently polymerized. During such process, the chirality of LHC18 was transferred to the PDA assemblies that show new chiroptical properties. Such chiroptical properties are based on the color change of PDA as well as the chiral transfer from LHC18 to PDA. Although all the stimuli investigated can trigger the blue gel into red one, the cut of the chiral transfer route by different stimulas is different. Heating can strength the chiral transfer and thus keep the chirality of the red gel phase and further produce the CPL. Other stimuli such as mechanical force, pH and many organic solvents break the chiral transfer and thus lead to the disappearance of the CD signals. Some other solvents such as cyclohexane, THF and methanol, which could not destroy or even strength the H-bond between LHC18 and DA, will maintain the supramolecular chirality of red gel. Therefore, both colorimetric and chiroptical signals can be applied simultaneously to detect selected organic solvents. So far as PDA sensing, we showed new insight into the chiral PDA system, which is expected to be used in some precise detections. Experimental


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Materials Preparation. All the starting materials and solvents were obtained from commercial suppliers and used as received. All chemical solvents were purchased from Beijing Chemicals. 10,12-Heptadecadiynoic acid, 10,12-pentacosadiynoic acid, 2,4- Heptadecadiynoic acid and 2,4-Heneicosadiynoic acid were purchased from TCI, respectively. The amphiphilic gelator (LHC18) containing L-histidine derivatives and octadecyl isocyanate were synthesized by following the method previously reported by our group. Milli-Q water (18.2 MΩ·cm) was used in all cases. Gels Formation in Organic Solvents. A typical procedure for the gels formation in mixed solvent of N, N- Dimethylformamide (DMF) and water is as follows: 5 mg LHC18 dissolved in 300ul DMF until absolutely transparent in a sealed tube, then adding the 300ul water into the prepared hot solution. Upon cooling to the room temperature, a gel was obtained quickly. Gelation was confirmed by the absence of flow, as observed by the tube inversion method. Photo-polymerization. the photo-polymerization of the gel was performed by irradiation with a UV lamp (λ=254nm, 25W) at a distance of 10 cm from the cell. The progress of the reaction was monitored by the UV-Vis spectra at different time interval. UV-Vis Absorption Spectra. UV-vis spectra were recorded in quartz cuvettes (light path 0.1 mm) on a JASCO UV-550 spectrometer. Fluorescent Microscopy. Fluorescent microscopy were recorded on the Olympus FV1000-IX 81 confocal microscope system with 100X oil immersion objective, using high pressure mercury lamp as excitation source for fluorescent images. Circular-Polarizing Filters Spectra. CPL measurements were performed with a JACSO CPL-200 spectrometer. 0.1 mm cuvettes were used for measuring the CPL spectra of samples.


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Fluorescence Emission Spectra. Fluorescence spectra were recorded in quartz cuvettes (light path 0.1 mm) on a Hitachi F-4500 fluorescence spectrophotometer. The EX slit and EM slit were set as 5 nm, and the PMT voltage was set as 400 V. Excitation wavelengths are specified in the corresponding figure caption. Circular Dichroism (CD) Spectra. CD spectra were recorded in quartz cuvettes (light path 0.1 mm) on a JASCO J-810 spectrophotometer. For the measurement of the CD spectra, the quartz cuvettes were placed perpendicular to the light path of CD spectrometer and rotated within the quartz cuvettes plane to rule out the possibility of the birefringency phenomena and eliminate the possible angle dependence of the CD signal. Scanning Electron Microscopy (SEM). SEM images were recorded on a Hitachi S-4800 FESEM instrument with an accelerating voltage of 10 kV. Before SEM measurement, the samples on silicon wafers were coated with a thin layer of Pt to increase the contrast. X-ray Diffraction (XRD). XRD analysis was performed on a Rigaku D/Max-2500 X-ray diffractometer (Japan) with Cu Kα radiation (λ=1.5406 Å), which was operated at a voltage of 40 kV and a current of 200 mA. Samples were cast on glass substrates and vacuum-dried for XRD measurements

ASSOCIATED CONTENT Supporting Information: Additional UV-Vis, Circular Dichoism (CD) spectra, FT-IR spectra and XRD pattern of various gels. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION


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Corresponding Author * Minghua Liu , E-mail: [email protected]. ACKNOWLEDGMENT This work was supported by the Basic Research Development Program (2013CB834504), the National Natural Science Foundation of China (Nos. 21473219, 21321063 and 91427302), and the Fund of the Chinese Academy of Sciences (No. XDB12020200). REFERENCES (1) Neabo, J. R.; Rondeau-Gagne, S.; Vigier-Carriere, C.; Morin, J.-F., Soluble Conjugated One-Dimensional Nanowires Prepared by Topochemical Polymerization of a ButadiynesContaining Star-Shaped Molecule in the Xerogel State. Langmuir, 2013, 29, 3446-3452. (2) Neabo, J. R.; Tohoundjona, K. I. S.; Morin, J.-F., Topochemical Polymerization of a Diarylbutadiyne Derivative in the Gel and Solid States. Org. Lett, 2011, 13, 1358-1361. (3) Rondeau-Gagne, S.; Neabo, J. R.; Desroches, M.; Larouche, J.; Brisson, J.; Morin, J.-F., Topochemical Polymerization of Phenylacetylene Macrocycles: A New Strategy for the Preparation of Organic Nanorods. J. Am. Chem. Soc, 2013, 135, 110-113. (4) Yoon, J.; Jung, Y. S.; Kim, J. M., A Combinatorial Approach for Colorimetric Differentiation of Organic Solvents Based on Conjugated Polymer-Embedded Electrospun Fibers. Adv. Funct. Mater, 2009, 19, 209-214. (5) Wang, D.-E.; Wang, Y.; Tian, C.; Zhang, L.; Han, X.; Tu, Q.; Yuan, M.; Chen, S.; Wang, J., Polydiacetylene liposome-encapsulated alginate hydrogel beads for Pb2+ detection with enhanced sensitivity. J. Mater. Chem. A, 2015, 3, 21690-21698.


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Fabrication of Helical Nanoribbon Polydiacetylene ... - ACS Publications

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