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Unprecedented Strong Photoluminescences Induced from the Both Aggregation and Polymerization of Novel Nonconjugated #-Cyclodextrin Dimer Xiaolin Guan, Donghai Zhang, Tianming Jia, Yang Zhang, Li Meng, Qijun Jin, Hengchang Ma, Dedai Lu, Shoujun Lai, and Ziqiang Lei Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b04979 • Publication Date (Web): 22 Mar 2017 Downloaded from http://pubs.acs.org on March 24, 2017

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Industrial & Engineering Chemistry Research

Unprecedented Strong Photoluminescences Induced from the Both Aggregation and Polymerization of Novel Nonconjugated β-Cyclodextrin Dimer Xiaolin Guan, * Donghai Zhang, Tianming Jia, Yang Zhang, Li Meng, Qijun Jin, Hengchang Ma, Dedai Lu, Shoujun Lai, Ziqiang Lei*

Prof. X. L. Guan, D. H. Zhang, T. M. Jia, Y. Zhang, L. Meng, Q. J. Jin, A. B. Prof. H. C. Ma, Prof. D. D. Lu, Prof. Z. Q. Lei Key Laboratory of Eco-Environment-Related Polymer Materials Ministry of Education, Key Laboratory of Polymer Materials Ministry of Gansu Province, College of Chemistry and Chemical Engineering, Northwest Normal University, Lanzhou, Gansu 730070, P.R. China Prof. S. J. Lai School of Chemical Engineering, Lanzhou University of Arts and Science, Lanzhou, Gansu 730070, P.R. China * E-mail: [email protected]; [email protected]

Abstract: Although the fascinating emission of natural carbohydrates containing a large number of glucose units have been found and attracted much interest due to their potential applications in biomedical areas, the cyclodextrin similar to these carbohydrate has unfortunately not show analogous luminescent behaviors at room temperature. The objective of this study is to realize the strong fluorescence of cyclodextrin containing no conventional chromophore.

In

this

work,

diethylenetriamino-styryl-bridged

a

new

bis

(β-

cyclodextrin) dimer and its polymer are synthesized by convenient methods, and strong blue photoluminescence is observed even with the naked eye under UV lamp. Studies on the molecular structure and the property of aggregation-induced emission (AIE) show that the strong fluorescence emission 1 - Environment ACS Paragon -Plus


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are produced by the intermolecular hydrogen bonding of amide and hydroxyl groups in aggregation states. Thus, this study opens a new route of synthesizing fluorescent cyclodextrin containing unconventional chromophores for cell imaging, biosensing, and drug delivery.

1. Introduction Organic fluorescent polymers have become a principal focus and hot topic in many fields due to their broad applications in solar energy conversion, chemical determination, cellular imaging, drug delivery, and so on. 1-7 The traditional fluorescent polymers are constructed by conjugated main chain or π-electron systems, which are covalently bonded to render sufficient conjugations. However, some inherent drawbacks of these fluorescent polymers, such as poor photostability, high cytotoxicity, nonbiodegradability, poor water solubility and complex synthesis process, are harmful to their practical applications. Moreover, traditional fluorescent polymers usually show “aggregation-caused quenching” (ACQ) effect at high concentration or in solid state, which also hamper their applications at higher levels and in wide areas.

8, 9

But in recent years, it has been found that a few kinds of polymer only containing auxochromophores or unconventional chromophores such as aliphatic tertiary amine, carbonyl, ester, and amide can also emit strong fluorescence and exhibit a remarkable “aggregation-induced emission” (AIE) effect.10,

11

Obviously, the luminescent polymers

containing unconventional chromophores are more environmentally friendly, easy to be prepared, and hydrophilic. What's more important is that they meet the requirement of inducing emission at high concentration or in solid state for applications. The first reported luminescent polymers containing unconventional chromophores were poly(amido amine) (PAMAM) dendrimers and hyperbranched poly(amido amine)s.12-16 A growing number of this kind of fluorescent polymers containing tertiary amine moieties, such as poly(amino ester)s (PAE), poly(ether amide)s (PEA), and polyureas (PURE), subsequently were developed. The 2 - Environment ACS Paragon -Plus

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luminogen of these polymers is associated with the N-branched tertiary amine moiety and the oxidation of the tertiary amine is assigned to the emitting source.17 Lately, some distinct polymers containing only carbonyl and ester groups are also found to be luminescent with the AIE effect.18-20 For example, fluorescent poly [(maleic anhydride)-alt-(vinyl acetate)],21 polyisobutene

succinic

anhydrides22

and

multiblock

polymer

derived

by

poly

(trithiocarbonate) of N-isopropyl-acrylamide were successively reported.23 Aggregation of multiple carbonyl groups induced emission is usually adopted to explain the mechanism of the emission, and the interaction between carbonyl and phenyl groups was also used to explain the unconventional emission. 11 β-cyclodextrin (β-CD), a class of cyclic oligosaccharides with 7 D-glucose units, are known to be highly water-soluble, essentially nontoxic, and excellently biocompatible.24, 25 In the past decades, fluorescent CDs have attracted a lot of interest and been extensively used as excellent fluorescent chemosensors for molecule recognition.26-29 At present, non-fluorescent β-CDs were frequently converted into fluorescent CDs by the covalent attachment of one or two fluorophores to the CDs. However, there are still some problems for this method. For example, multiple complicated reactions are usually required during the procedure of the fluorescent labeling. Moreover, what's worse is that the attachment of organic fluorescent dyes might change the physical or chemical properties of β-CD and result in a negative effect on the nontoxic property and biocompatibility. Therefore, the exploration of luminescent βCD derivative containing unconventional chromophores is very attractive in the field of chemosensors and biological probes. Recently, Tang and co-workers reported an amazing discovery that rice is luminescent and emits a bright blue light at 382 and 433 nm, respectively.11, 30 Since starch is the major component of rice and is comprised of a large number of glucose units jointed by glycosidic bonds, multiple hydrogen bonds induced by the presence of oxygen atoms and hydroxyl groups is supposed to play an important role in its emission. It is well known that β-CD is 3 - Environment ACS Paragon -Plus


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produced in industrial quantities by the enzymatic degradation of starch.31,

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32

As a

carbohydrate similar to starch, it's theoretically possible that β-CD could be found the fascinating emission. However, it is regretful that β-CD does not show analogous luminescent behaviors at room temperature. Compared with starch, the inadequate numbers of electronrich units like oxygen and nitrogen atoms and weak hydrogen-bonding interactions in β-CD are the major reasons. Can β-CD derivative containing unconventional chromophores by adding on the quantity of oxygen and nitrogen atoms to increase hydrogen-bonding interactions emit light? There are few researches related to the issues of luminescent β-CD derivative containing unconventional chromophores have been conducted. Zhu and co-authors synthesized a strong fluorescent of (HPAA-CDs) based on the hyperbranched poly (amido amine)s (HPAAs) containing different amounts of β-CD.33 They found the introduction of big β-CD molecules enhanced the molecular rigidity of HPAA greatly, resulting in a dramatic improvement of photoluminescence. However, this is not an ideal method to prepare the fluorescent β-CD through introducing hyperbranched molecule due to the relatively complex synthesis procedure and irregular structure. Despite several works being conducted on the research of inherent fluorescence from β-CD derivative, the types of luminescent β-CD containing sample structure with oxygen and nitrogen atoms derivative are still very limited. Compared with hyperbranched polymers, some their linear analogues with sample and well defined structure are also found having the inherent fluorescence emission. For example, Chen studied the intrinsic photoluminescence properties of hyperbranched polyethylenimines (PEIs) and their linear counterpart (LPEIs) in absence of any classical fluorescent probes.34 The results indicated that linear polyamines are capable of producing strong intrinsic photoluminescence species without need of having a tridimensional branched structure. In this paper, aiming at obtaining strong fluorescent β-CD derivative containing unconventional chromophores with simple structure and synthetic method, we design and synthesis of a novel 4 - Environment ACS Paragon -Plus

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luminescent diethylenetriamino-styryl-bridged bis (β-cyclodextrin) dimer in the absence of any type of fluorescent probes (Scheme 1). Meanwhile, we systematically discuss the inherent fluorescence properties exhibited from the β-CD dimer and its polymer, which respectively originate from the aggregation by hydrogen bond and polymerization. To the best of our knowledge, this is the first example to use short linear ethylenimine to prepare the strong luminescent β-CD derivative with simple synthetic method. Moreover, it is worth being mentioned that the inclusion capability of the β-CD cavities in luminescent β-CD dimer and its polymer provides a possible application in the combination of biofluorescence imaging and drug delivery. OTs

TsCl

+

NaOH / H2O

β-CD

H2N

H N

KI NMP

NH2

6-OTs-β-CD H N

N H

NH2

+

DCC, HOSu HOOC

6-DETA-β-CD

O

NH

NH

HN

HN

NH

β-CD dimer

DMF

VPA

O

HN

COOH

O

K2S2O8

n

O

HN

H2O, N2 NH

HN

NH

HN

NH

poly(β-CD dimer)

Scheme 1. Synthetic routes towards β-CD dimer and poly (β-CD dimer).

2. Results and Discussion 2.1. Synthesis and Characterization of β-CD dimer and poly (β-CD dimer)

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The diethylenetriamino-styryl-bridged bis (β-cyclodextrin) dimer and its polymer were synthesized according to the synthetic routes shown in Scheme 1 and the detailed synthesis processes were shown in the Supporting Information. The β-CD dimer was synthesized in satisfactory yields starting from 6-O-monotosyl-βcyclodextrin (6-OTs-β-CD) by two-step reaction. Firstly, diethylenetriamine was connected with the β-CD from 6-OTs-β-CD using KI and N-methyl-2-pyrrolidone (NMP). 35, 36 Then, βCD dimer was synthesized by condensation reaction between amino (-NH2) in 6-DETA-β-CD and carboxyl (-COOH) in 2-vinylterephthalic acid (VPA) using dicyclohexylcarbodiimide (DCC) and N-hydroxysuccinimide (HOSu) in N, N-dimethylformamide (DMF). Polymer was synthesized by sample free radical polymerization in water using potassium persulfate (K2S2O8) as initiator. The β-CD dimer was characterized by 1H NMR,

13

C NMR (Figure S1, Supporting

Information), Fourier transform infrared (FT-IR) and mass spectrometry (MS) from which satisfactory analysis data were obtained. In the 1H NMR spectrum of β-CD dimer in DMSOd6, the new strong peaks at 7.86 ppm (imino group, -NH-), 2.64 ppm (methylene unit, -CH2linked with amide group) and 2.80 ppm (methylene unit, -CH2- linked with imino group) are assigned to the presence of the diethylenetriamine structure (Figure 1). Moreover, the new peaks present at the aromatic region of the 1H NMR spectra with chemical shift around 7.378.04 ppm and two characteristic peaks of vinyl group at 5.29 and 6.88 ppm indicate the conjugation of VAP to the β-CD dimer (Figure 1). Additionally, the formation of β-CD dimer is verified by the characteristic band for the amide group at 1659 cm-1 and the enhancement of the methylene peak at 2928 cm-1 in IR spectra (Figure S2, Supporting Information). The poly (β-CD dimer) was characterized by 1H NMR, FT-IR, and gel permeation chromatography (GPC) with polystyrene standards. 1H NMR spectra of the polymer show similar peaks to those in the spectrum of β-CD dimer except the absence of two characteristic 6 - Environment ACS Paragon -Plus

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peaks of vinyl group at 5.29 and 6.88 ppm, indicating the polymerization of the β-CD dimer (Figure 1). Additionally, the IR spectra of poly (β-CD dimer) also shows the characteristic band for the amide group at 1658 cm-1 and the methylene peak at 2930 cm-1, which is same as the IR spectra of β-CD dimer (Figure S2, Supporting Information). The result indicates that the structure of β-CD dimer was not destroyed during polymerization. The numberaverage and weight-average molecular weights of polymer were estimated to be 1.8 ×104 and 3.8×104, respectively, using GPC (Table S1, Supporting Information). The low degree of polymerization of dimer (n = 7) is probably induced by the strong stereo-hindrance effect.

Figure 1. 1H NMR spectra for β-CD dimer and poly (β-CD dimer ) in DMSO-d6. 2.2. Fluorescence of β-CD dimer and poly (β-CD dimer) We found with surprise that the aqueous solutions of β-CD dimer and poly (β-CD dimer) containing unconventional chromophores exhibit strong fluorescence, whereas the purified β-CD exhibits no fluorescence in visible light area (Figure 2). Meanwhile, We found that the poly (β-CD dimer) shows much stronger fluorescence with a maximum emission 7 - Environment ACS Paragon -Plus


wavelengths (λem) around 410 nm under the excitation at 300 nm compared with the β-CD dimer with λem around 460 nm under the excitation at 350 nm at the same concentration. The fluorescence quantum yield of β-CD dimer and poly (β-CD dimer) in solid are measured to be 3.23% and 5.31%，respectively. The fluorescence quantum yield of poly (β-CD dimer) is higher than β-CD dimer, which indicates that the aggregation-induced emission of poly (β-CD dimer) is stronger than β-CD dimer due to the higher degree of aggregation after polymerization. Moreover, the blue-shift in the emission spectra of β-CD dimer and poly (βCD dimer) is caused by the suppression of vibrational relaxation in the excited state.37 A question arising is what is the origin of the photoluminescence of dimer and polymer in solvents in absence of any type of fluorescent probes? Tang and co-workers have proposed the mechanism for the luminescence of natural polymers contain no conventional chromophore.

11

They pointed out that natural polymers are non-emissive because of the

absence of chromophore with sufficient electronic conjugation when molecularly isolated. However, the structural rigidification immediately takes place upon aggregation. As a result, the electron-rich units like oxygen and nitrogen atoms form clustoluminogens with smaller energy gaps and more extended electronic conjugations in the aggregates. 11 That is to say, strong and multiple hydrogen bonds existing in natural polymers due to the presence of oxygen atoms and nitrogen atoms should play a important role in the emission.

β -CD dimer polymer

poly(β-CD dimer)

600

Flourescence Intensity

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Ex

500

Em

400 β-CD dimer

300 200 100

β-CD

0 250

300

350

400

450

500

Wavelength (nm)

8 - Environment ACS Paragon -Plus

550

600

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Figure 2. Excitation spectra (left) and fluorescence spectra (right) of 1mg mL-1 β-CD, β-CD dimer and poly (β-CD dimer) in aqueous solution. (Inset: the photographs of β-CD, β-CD dimer and poly (β-CD dimer) in water under 365 nm UV light irradiation. In order to prove that the fluorescence of β-CD dimer is not induced by phenyl ring, we successfully synthesized diethylenetriamino-methylene-bridged bis (β-cyclodextrin) dimer (PCD) and the structure of PCD could be confirmed by FT-IR and 1H NMR (Figure S2 and Figure S3, Supporting Information). It is interesting that PCD shows much stronger fluorescence with maximum emission wavelengths (λem) around 448 nm under the excitation at 355 nm (Figure S4, Supporting Information). Compared with the β-CD dimer, the molecule structure of PCD is not containing phenyl ring, but the blue photoluminescence can be observed at high concentration. So we could conclude that the aggregation of oxygen atoms and nitrogen atoms is the main reason of the emssion of β-CD dimer. To identify that the fluorescence of β-CD dimer are induced by the multiple hydrogen bonds in the aggregates, the concentration and poor solvent effects on the emission of β-CD dimer were investigated, respectively. 2.3. AIE properties of β-CD dimer β-CD dimer shows good solubility in aqueous solution. When the dilute aqueous solutions of β-CD dimer at low concentrations ranging from 10-5 to 5×10-4 mol L-1 are excited at 360 nm, no visible photoluminescence (PL) is observed with rather low emission signals being recorded (Figure 3a). However, the fluorescence intensities at 450 nm of β-CD dimer increase intensely as the concentration increases from 10-3 to 5×10-2 mol L-1, and the emission of β-CD dimer has been lighted up at high concentration (Figure 3a). So, the above results indicate the AIE feature of β-CD dimer, which is induced by the multiple hydrogen bonds in the aggregates. Another experiment is arranged to add ethanol into β-CD dimer aqueous solution. Ethanol is chosen because it is a typical nonsolvent for β-CD dimer: the 9 - Environment ACS Paragon -Plus

dimer must


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aggregate in the aqueous mixtures with massive ethanol. Fluorescence spectra of β-CD dimer in water/ethanol system are shown in Figure 3b. Obviously, the fluorescence intensity of βCD dimer was increased in a nonlinear fashion with the volume fraction of ethanol increases. Meanwhile, β-CD dimer gives a bright blue emission with maxima at ~460 nm in the 10/90 water/ethanol mixture. This kind of light emission is termed as rigidification-induced emission (RIE). 38 With the volume fraction of ethanol increased, the dimer is less soluble in the water-ethanol system and more aggregated. As a result, the increasing of non-covalent intermolecular hydrogen bond interaction makes the aggregation of electron-rich units like oxygen and nitrogen atoms, which cause strong fluorescence. Because of the amide and hydroxyl groups carrying the rambling and ramshackle lone-pair electrons can vibrate and rotate, the β-CD dimer is non-emissive when dispersed in good solution. With the poor solution added, the aggregation of amide and hydroxyl groups occurs and the molecular conformation becomes rigidified. The electron clouds of electron-rich atoms are overlapped and shared, so the intermolecular through-space conjugation is coming into being, and blue photoluminescence can be observed in high volume fraction of ethanol solution.

Figure 3. (a) Fluorescence spectra of β-CD dimer at different concentrations (λex = 360 nm) and photographs under UV light (365 nm) at different concentrations. (b) Fluorescent spectra

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of 10-4 mol L-1 of β-CD dimer in different ethanol fractions (λex = 360 nm) and photographs of β-CD dimer under UV light (365 nm) in water/ethanol system. 2.4. Fluorescence Mechanism Figure 4a illustrates that the variety of fluorescence intensity of β-CD dimer solution with different temperature. The molecular motion is restricted at low temperature and tends to form clusters of various sizes, which caused the aggregation of amide and hydroxyl groups. Compared with the isolated molecules, the resulting clusters have smaller energy gaps and more extended electronic conjugations. With increased temperature, the intermolecular hydrogen bond is constantly damaged and molecular motion is becoming increasingly free. As a result, the fluorescence intensity of β-CD dimer is decreased because the degree of aggregation of amide and hydroxyl group is gradually weakened. In order to confirm the explanation as discussed above and gain deep insight into the temperature effect on the fluorescence of β-CD dimer, the temperature-variable 1H NMR analysis of the hydrogen bond in the β-CD dimer solution was performed. Two protons signals of -CO-NH- with δ= 7.86 ppm and -OH with δ= 5.65 ppm are chosen and discussed, since the corresponding protons signals can be affected by hydrogen bonding and therefore can provide the information about the hydrogen bonding between the amide and hydroxyl groups. Figure 4b shows the 1H NMR spectra of β-CD dimer recorded from 25 to 65 °C. It indicates the typical characteristic signal of -CO-NH- weakening and slightly shifting to high-filed, and the typical characteristic signal of -OH weakening and shifting to high-filed upon heating at temperature. These changes indicate the existence of intermolecular hydrogen bonding is disrupted with elevating temperatures.39 Therefore, the decreasing of fluorescence intensity of β-CD dimer can be ascribed to the weakened hydrogen bonding.



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Figure 4. (a) Fluorescence spectra for 5×10-3 mol L-1 of β-CD dimer in water at the different temperature from 0 to 70 °C (λex = 360 nm). (b) 1H NMR spectra for β-CD dimer at the different temperature from 25 to 65 °C in DMSO-d6. Moreover, the effects of pH on the fluorescence intensity of β-CD dimer also indicated that the fluorescence emission of β-CD dimer was produced by the intermolecular hydrogen bonding in aggregation states. The comparative tests at various pH values showed the relative fluorescence intensity of β-CD dimer changed with pH (Figure S5, Supporting Information). The results show that the fluorescence intensity is relatively stable in the pH range 3 to 11 while it decreased in either strong acid or strong base. Especially, the fluorescence intensity is reduced sharply with further basification from pH = 11 to pH = 13. It is well known that the intermolecular hydrogen bonding is easily destroyed by adding of the NaOH, which will cause the change of original aggregation state. The SEM images of β-CD dimer at strong alkali solution with pH =13 (Figure S6, Supporting Information) confirms the changing of aggregation state compared with the self-assemble morphology of the β-CD dimer at neutral condition (Figure 5a). It could be observed that the surface of aggregate is peeled and tend to curl, which caused by the fracture of hydrogen bond at strong alkali solution.


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Figure 5. SEM images of (a) β-CD dimer in highly concentrated solution; (b) β-CD dimer in solid state; (c) dried gels of β-CD dimer; (d) poly (β-CD dimer ) in highly concentrated solution; (e) Schematic illustration of the possible mechanism of nanofibers formation for βCD dimer in aggregate state. Furthermore, in 1H NMR spectra of β-CD dimer (Figure 1), the resonance intensity ratio of the peak h+j, due to two amino –NHs, to peak f, due to one amido –NH, is less than 2. The result indicates that the amino groups neighboring to CD ring are more restricted in rotation motion due to the intermolecular hydrogen bonding between amino –NHs in aggregation states. As a result, the conformational exchange of CD ring is also hampered and the extent of restricted intramolecular rotation (RIR) is enhanced, which induces the aggregation-induced emission. After polymeration, the resonance intensity ratio of the peak h+j to peak f is more smaller in 1H NMR spectra of poly (β-CD dimer) (Figure 1) due to the higher degree of aggregation. As a result, the conformational exchange of CD ring in poly (β-CD dimer) is further hampered and the AIE is reinforced when compared with β-CD dimer in the same concentration (Figure 2). The results indicate that both the amido group and the cyclodextrin (CD) ring are responsible for the AIE property because the electron clouds of electron-rich atoms of oxygen and nitrogen atoms are overlapped and shared in aggregate state. As we discussed above, the AIE by the intermolecular hydrogen bonding is the reason for the luminescence of β-CD dimer. In order to obtain more information about the aggregate 13 - Environment ACS Paragon-Plus


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behavior, the SEMs of β-CD dimer under different aggregate states, such as in highly concentrated solution, hydrogel state, solid state, and poly (β-CD dimer) were researched, respectively (Figure 5). In Figure 5a and Figure 5b, micrographs display very distinct fibrillary morphologies-like aggregates for β-CD dimer in solution and solid state. The fibers become more intertwined in solid state and the fluorescence emission become stronger. Meanwhile, after polymerization, the fibers of poly (β-CD dimer) also become more intertwined and the fluorescence emission is reinforced when compared with β-CD dimer in the same concentration (Figure 5d). The results indicate that the higher degree of aggregation is, the stronger luminescence of β-CD dimer is. The schematic representation of a possible aggregation mode is described as Figure 5e. A large number of hydroxys and amide groups of β-CD dimer can form strong and stable intermolecular hydrogen bonds, which caused the compact aggregation

40

and nanofiber structures. Moreover, the representative porous

aggregates obtained from dried gels of β-CD dimer when dissolved in the water and cooled down to the room temperature (Figure 5c) and the gels of β-CD dimer emits a bright blue light. On the basis of the information discussed above, it could be believed that in aggregation states, the amide and the hydroxyl units in β-CD dimer and poly (β-CD dimer) might form through-bond and through-space electronic conjugations due to the multiple hydrogenbonding interactions. Such conjugations are further reinforced by the formation of intermolecular hydrogen-bonds, giving rise to the strong emission. So, the SEM confirms that the intermolecular hydrogen bond is an important driving force for aggregate into the selfassembly structure.

3. Conclusions In this paper, we constructed a new luminescent β-CD dimer and its polymer containing noconventional chromophore and proved that the fluorescence emission originated from the intermolecular through-space conjugation by the hydrogen-bonding self-assembly of amide and hydroxyl groups in aggregation states. It was interesting that as the degree of aggregation 14 - Environment ACS Paragon-Plus

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increased in different states, the fluorescence emission intensity of the β-CD dimer increased rapidly. Meanwhile, an obvious AIE phenomenon was observed in the water-ethanol system. Compared with those fluorescent β-CDs by the covalent attachment of fluorophores in traditional ways, the β-CD dimer and polymer were synthesized by convenient methods and could emit strong luminescence with the nontoxic properties and biocompatibility. What is more, these results demonstrate that in the absence of high conjugated system, the nonfluorescen β-CD can also emit light fluorescence due to the clustering of oxygen and nitrogen functional groups. This research is aimed at providing a new route of synthesizing fluorescent β-CD derivative containing unconventional chromophores for cell imaging, biosensing, and drug delivery.

Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: Experimental section, FTIR spectrum of β-CD, β-CD dimer, poly (β-CD dimer) and PCD, 1H NMR spectrum and Fluorescence spectra of PCD, 13C NMR spectrum β-CD dimer, as well as SEM images of β-CD dimer and GPC data of poly (β-CD dimer).

Acknowledgements: Funding was partially provided by National Natural Science Foundation of China (51363019) and Specialized Research Fund for the Doctoral Program of Higher Education of China (20136203120002).

Keywords:

aggregation-induced

emission;

β-cyclodextrin

unconventional chromophores; fluorescence

References


dimer;

polymerization;


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For Table of Contents Only

A new luminescent β-cyclodextrin dimer and its polymer containing noconventional chromophore are synthesized by convenient methods. Studies on the property of AIE show that the fluorescence emission originated from the intermolecular through-space conjugation by the hydrogen-bonding self-assembly of amide and hydroxyl groups in aggregation states. The study opens a new route of synthesizing non-toxic fluorescent cyclodextrin for biological application.


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Unprecedented Strong Photoluminescences ... - ACS Publications

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