SCIENCE CHINA Chemistry •  MINI REVIEWS  •

doi: 10.1007/s11426-017-9070-1

· SPECIAL TOPIC · Porous Organic Polymers

Chiral covalent organic frameworks for asymmetric catalysis and chiral separation Guofeng Liu1, Jianhui Sheng1,3 & Yanli Zhao1,2* 1

Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore 2 School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore 3 Department of Macromolecular Science, Fudan University, Shanghai 200433, China Received March 24, 2017; accepted April 24, 2017; published online July 3, 2017

Covalent organic frameworks (COFs), covalently assembled from the condensation reactions of organic building blocks, are a fascinating class of functional porous materials with two- or three-dimensional crystalline organic structures. Generally, it is preferable to use symmetric and rigid building blocks to construct highly crystalline COFs with desired topology. On the other hand, the incorporation of chiral functional moieties in the building blocks would open up new applications such as asymmetric catalysis and chiral separation. This mini review highlights the principle strategies in the design and synthesis of chiral COFs. The interesting and potential applications of these chiral COFs for asymmetric catalysis and chiral separation are also summarized. This mini review aims to provide an up-to-date advancement of chiral COFs for asymmetric catalysis and chiral separation. asymmetric catalysis, building blocks, chiral separation, covalent organic frameworks, porous materials

Citation:

Liu G, Sheng J, Zhao Y. Chiral covalent organic frameworks for asymmetric catalysis and chiral separation. Sci China Chem, 2017, 60: doi: 10.1007/ s11426-017-9070-1

1   Introduction Covalent organic frameworks (COFs) are porous crystalline polymers assembled from organic building blocks through covalent bonds in a process termed reticular synthesis. Thanks to Yaghi and co-workers’ seminal work in 2005 [1], the reticular synthesis of COFs with extended two- or threedimensional (2D or 3D) structures entirely composed of light elements (such as boron, carbon, nitrogen, oxygen, and silicon) and reticulated organic molecules formed by covalent bonds via condensation reactions has been conceptually proposed. Since then, both chemists and materials scientists have exploited this concept in order to construct specific COFs with varying topological structures and complexity *Corresponding author (email: [email protected]) © Science China Press and Springer-Verlag Berlin Heidelberg 2017

[2–4]. Thus, extending the condensation reactions to make covalently linked 2D or 3D organic crystalline frameworks with high architectural and chemical robustness has been a long-standing objective. To date, more than one hundred COF structures with reticular porous frameworks have been rapidly produced by the condensation reactions of multi-dentate organic molecules linked by covalent bonds such as B–O, C=N, C=N(Ar), C=C, C–N, and B=N [5–14]. When constructing a 2D or 3D COF based on a desired topology, it is preferable to use rigid and well-defined molecular building blocks that remain unchanged during the preparation process. The challenge is that such a reticulation process must be carried out under synthetic conditions that maintain the integrity of the molecules, while allowing for microscopic reversibility in order to afford ordered crystalline products. In addition, the molecular chem.scichina.com   link.springer.com

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units used in reticulation to form specific linkages must possess in a chemically and geometrically defined fashion. In general, the reactions that fulfill the thermodynamically stable crystalline architectures are still very limited. Many organic building blocks and synthetic methods (such as solvothermal reaction and microwave-assisted method) have been employed, but finding suitable synthetic conditions for the construction of COFs is not easy. Presently, the vast majority of COFs are prepared by solvothermal reactions that include some special experimental conditions such as having reactions in a sealed and inert atmosphere, long reaction time, high temperature and right solvent composition. Finding appropriately operated conditions is the key to afford high quality of COFs, since these parameters ensure the fine balance between the reversibility of the reactions and the rate of crystallization [15].

advanced materials. 3.1   Strategic design of chiral COFs Chiral COFs remain difficult to be synthesized because crystallinity, porosity, and chiral functionality have to be simultaneously taken into account. The key bottleneck of constructing chiral COFs is the intrinsic mismatch between the symmetry for crystalline structure and asymmetry for chiral functionality. Generally, there are two approaches to introduce the chiral functional units into the networks of COFs: post-synthetic modification and bottom-up strategy.

3   Chiral COFs

3.1.1  Post-synthetic modification Post-synthetic modification has been extensively used to design or tailor the organic and inorganic functionalization onto the preformed frameworks of COFs [69,70]. Thus, it is a facile approach to fabricate the chiral COFs via post-modification of achiral porous supports with chiral moieties. Jiang and co-workers [71] successfully constructed a type of imine-linked chiral COFs by pore surface engineering. The chiral COFs consist of three-components: 5,10,15,20-tetrakis(4'-tetraphenylamino) porphyrin, 2,5-bis(2-propynyloxy) terephthalaldehyde (BPTA), and 2,5-dihydroxytere-phthalaldehyde (DHTA). In this COFs system, the porphyrin units occupy the vertices of COFs network, and a mixture of BPTA and DHTA are located at the edge of frameworks with varying molar ratios. By integrating the ethynyl groups with different content into the edge, the chiral pyrrolidine units are subsequently anchored quantitatively into the framework through post-synthetic modification of click reaction (Figure 1). Thus, the density of chiral pyrrolidine units in the pore channels can be systematically designed and controllably synthesized by this engineering methodology. This strategy, however, leads to uneven distribution and less loading of chiral functionalities. In addition, not all chemical functionalities can be modified into the pores of COFs. For example, the covalent bonds may be too strong to be sufficiently reversible. Therefore, some functionality units must be added into existing frameworks.

In the recent years, chiral porous materials have emerged as an attractive research area toward promising applications in catalysis, separation, and recognition. In this regard, porous crystalline chiral COFs with well-defined structures are highly desired for applications in chiral separation, and asymmetric heterogeneous catalysis. However, the establishment of chiral COFs is still a hard bone because it has to achieve simultaneously the balance and conflict of asymmetry and crystallinity. To date, only a few chiral COFs have been successfully constructed due to their challenging synthesis, although the incorporation of suitable chiral moieties in the building blocks of COFs would afford some exciting

3.1.2  Bottom-up strategy The direct construction of porous materials from chiral building blocks with enantiomeric purity is a promising but challenging approach. Very recently, Yan et al. [72] developed a bottom-up approach to produce chiral COFs for high-resolution chromatographic application. In this work, the chiral monomer CTp was firstly synthesized by the esterification reaction of 1,3,5-triformylphloroglucinol (Tp) and (+)-diacetylL-tartaric anhydride. Three chiral COFs were then obtained by the condensation of CTp with 1,4-phenylenediamine, benzidine (BD) and 2,5-dimethyl-p-phenylenediamine, respectively (Figure 2). Considering good solvent and thermal sta-

2   Functionalization of COFs While the reticular synthesis of COFs is still at an early stage of its development, currently, the field is mostly driven by potential future applications together with investigating the basic chemistry of the frameworks and the design principles. Owing to strong covalent interactions between light elements, COFs possess a number of unique features such as rigid structures, low densities, high thermal and chemical stability, permanent porosity, and large surface areas, which make them highly promising in gas storage [16–23] and separation [24–26]. Similarly, owing to their large surface areas and porosities, COFs have also been considered for catalytic applications [27–29]. In addition, the incorporation of suitable functional moieties or groups in the building blocks would open up new potentials as advanced materials for applications in energy conversion and storage [30–37], environmental conservation [38–41], photocatalysts [42–44], photoluminescence [45,46], chemical sensors [47–51], proton conduction [52–63], semiconductors [64], and drug delivery and release [65–68].

 

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   (a) Figure 1        Illustration for the synthesis of imine-linked chiral COFs via the strategy of post-synthetic modification; (b) a graphical representation of chiral COFs with different densities of catalytic sites on the pore walls. Adapted with permission from Ref. [71], Copyright 2014 the Royal Society of Chemistry (color online).

   Schematic Figure 2        illustrations for the synthesis of chiral COFs based on CTp and their bound capillary columns. Reprinted from Ref. [72], Copyright 2016 Macmillan Publishers Ltd. (color online).

bility of these chiral COFs, the authors subsequently established chiral COF-bound capillary columns under an in situ synthesis strategy to perform high-resolution chiral separation. Different from the incorporation of the chiral centers in the building blocks of Tp, Wang and co-workers [73] developed two chiral COFs, named LZU-72 and LZU-76, by directly reticulating achiral Tp and dianiline-functionalized chiral pyrrolidine units together. In this work, the key design is that the chiral pyrrolidine moieties are incorporated into the middle phenyl ring to afford the rigid building block of 4,4'-(1H-benzo[d]-imidazole-4,7-diyl)di-

aniline, which not only perfectly maintain the rigidity of the 4,4'-diamino-p-terphenyl backbone, but also can effectively employ the chirality of pyrrolidine. The building block of (S)-4,4'-(2-(pyrrolidin-2-yl)-1H-benzo[d]imidazole-4,7-diyl)dianiline anchored with chiral pyrrolidine was then successfully synthesized and used for the production of chiral COFs (Figure 3). This facile strategy perfectly integrates the asymmetric chirality with the symmetric backbone. The method is highly versatile to attach different chiral moieties for the construction of various chiral COFs. In fact, all the chiral COFs discussed above are prepared by attaching or anchoring the chiral functionalities on the walls

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   Schematic Figure 4        synthesis of the chiral COFs embedded with chiral skeleton. Reprinted with permission from Ref. [74], Copyright 2016 the American Chemical Society (color online).

   Schematic Figure 3        representation for the direct construction of chiral COFs, LZU-72 and LZU-76. Reprinted with permission from Ref. [73], Copyright 2016 the American Chemical Society (color online).

of frameworks rather than embedding in the frameworks. In a different approach, Cui et al. [74] selected enantiopure tetraaryl-1,3-dioxolane-4,5-dimethanol (TADDOL)-derived tetraaldehyde condensed with 4,4'-diaminodiphenylmethane to form 2D COFs, where the chiral function is embedded into the frameworks (Figure 4). In this work, TADDOLs possess versatile chiral auxiliaries and distribute four aryl substituents in propeller type conformation, which are beneficial to promote crystalline COF growth. In addition, the 1,4-diol moiety in TADDOLs is helpful to form intramolecular and intermolecular hydrogen bonding, thereby providing structures with particular rigidity. Due to the strong hydrogen-bonding ability and a parallelogram arrangement of the coplanar aldehyde groups associated with a semirigid backbone, two 2D chiral COFs were successfully produced and used as efficient heterogeneous catalysts for the asymmetric addition of diethylzinc to aldehydes. 3.2   Applications of chiral COFs Most of the interesting applications produced from COFs are highly associated with their conjugated structures and ordered

nanopores. Compared with the short-range structural order of traditional covalent polymers, COFs contain the organic subunits with reversible covalent bonds that tend to form well-defined crystalline structures with regular pore channels, which could potentially work as organic zeolites. In addition to the high coordination of the nitrogen atoms with various metal ions, imine-based COFs exhibit quite good stability in most organic solvents, water, acid, and base [75]. All of these features make imine-based COFs possessing a great potential in the heterogeneous catalysis [69]. COFs are typically crystallized under mild conditions, which may allow the construction of chiral COFs by rational choices of enantiopure building blocks or templates. Chiral COFs are of particular interest because of the increasing demand of advanced materials for heterogeneous asymmetric catalysis and chiral separation. The chiral COFs catalysts combine lots of remarkable features, such as enhanced activity, excellent recyclability, broad applicability, and high capability. And they can remain well catalytic performance even under continuous flow conditions. Although a number of COFs with smart functions such as proton-conducting have been reviewed [63], the brief summary of chiral COFs used for asymmetric catalysis and chiral separation are still not reported. 3.2.1  Asymmetric catalysis One of the unavoidable problems of organic catalysis in heterogeneous systems is the expensive cost of catalysts lacked good recyclability. However, most heterogeneous catalysts rooted in linear polymer carriers display low activities to the

 

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catalytic sites. Thus, it is necessary to develop immobilized, easily recoverable and reusable catalysts. In order to develop chiral COFs as effective heterogeneous asymmetric catalysts, some critical prerequisites must be met. Firstly, the COF catalysts should remain the integrity under the conditions of high temperature and display high stability in complex solvent environments such as water, acid, base, and most of organic solvents. Next, there should be some chiral catalytic active sites embedded or attached in the networks of COFs. Fortunately, COFs constructed from Schiff-base chemistry display high stability in organic solvents and water, thus they meet the first criterion as robust organic catalysts. In addition, by taking advantage of post-synthetic modified approach and bottom-up synthetic strategy, chiral functional moieties can be successfully introduced into the imine-based COF networks, which provide chiral catalytic active sites for asymmetric catalysis. These facts strongly motivated both chemists and materials scientists to explore the performance of chiral COFs as heterogeneous catalysts in asymmetric catalysis. During recent few years, chiral COFs have been successfully demonstrated as heterogeneous catalysts and showed excellent catalytic performance in classical asymmetric catalysis. Jiang et al. [71] demonstrated an example for the fabrication of chiral COFs by the post-synthesis modification. In this work, S-pyrrolidine units were successfully employed to functionalize the pore channel of COFs with chiral moieties. The functionalized chiral COFs were then applied as metal-free heterogeneous catalysts for chiral organocatalysis with high activity, excellent enantioselectivity and good recyclability. Due to the pore surface engineering, the density of chiral pyrrolidine units on the networks can be systematically designed and controllably synthesized, which subsequently influences the crystallinity, porosity and catalytic activities. In addition, this research team also constructed a 2D COFs with high stability, good crystallinity and excellent porosity through the reinforcement of interlayer interactions [76]. After modified through post-synthetic functionalization, two distinct chiral COFs were produced by appending chiral units and catalytic sites on their pore walls. Similarly, the catalytic nano-space can be fine-tuned by the percentage of chiral functional groups introduced in the building blocks (Figure 5). Notably, the catalytic nano-space with different sizes plays a key role in tuning the activity of the metal-free catalysts. The resulting chiral COF-based catalysts display high activity, good enantioselectivity, recyclability and environmental benignity in Michael addition reactions in water under ambient conditions. The COF catalysts could retain the original crystalline structure after treating with various solvents for one week, indicated by powder X-ray diffraction and Brunauer-Emmett-Teller (BET) experiments (Table 1). Wang et al. [73] reported that two chiral COFs attached with pyrrolidine on the walls of networks could act as struc-

   Schematic Figure 5        representations for the channel-wall structure of chiral organocatalytic COFs. Reprinted with permission from Ref. [76], Copyright 2015 Macmillan Publishers Ltd. (color online).

Table 1   BET surface area, pore sizes, and stability of some chiral used for catalysis COFs

BET surface area (m2/g)

Pore size (nm)

Stability a) (°C)

Ref.

LZU-72

1114

1.3–2.0

450

[73]

LZU-76

758

1.2–2.2

300

[73]

CCOF-1

266

1.02

380

[74]

CCOF-2

335

1.06

380

[74]

[Pyr]x-H2P-COF [(S)-Py]x-TPBDMTP-COFs

63–960 1612–1970

1.4–1.9 2.86–3.07

r.t.

b)

[71]

400

c)

[76]

a) The temperature was measured by thermogravimetric analysis; b) room temperature in water/EtOH (1:1, v/v); c) the structure of the COF remains stable after treating in organic solvents (dimethyl formamide (DMF), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), MeOH, and cyclohexanone), water (100 °C), NaOH aqueous solution (14 mol/L), or HCl aqueous solution (10 mol/L) for one week.

turally robust and highly active heterogeneous organocatalysts. The chiral COFs displayed robust structural stability and highly chemical stability even under acidic conditions. The straight channels within these two crystalline COFs could provide efficient access to the chiral-pyrrolidine sites for heterogeneous organocatalysis. The COFs exhibited excellent

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enantioselectivity and easy recyclability in the asymmetric aldol reactions to afford the desired aldol products. Moreover, Cui et al. [74] constructed 2D COFs with chiral functionalities embedded into the frameworks by imine condensations of enantiopure TADDOL-derived tetraaldehydes with 4,4'-diaminodiphenylmethane. Taking advantage of the chiral dihydroxy groups encoded into the skeleton of COFs, the chiral COFs with high stability in organic solvents were employed as efficient and recyclable heterogeneous catalysts for asymmetric addition of diethylzinc to aldehydes with high enantioselectivity (Figure 6). The results greatly expand the scope of chiral COF materials design and applications in practically useful enantioselective processes. 3.2.2  Chiral separation On account of the large surface area, ordered and permanent porosity, good solvent stability and high thermal stability, COFs should be a good candidate to be used for separation of small molecules both in high resolution gas chromatography (GC) and high performance liquid chromatography (HPLC) [77,78]. Meanwhile, the separation of enantiomers is a requisite in pharmacology and biology because of profoundly different pharmacology and biological interactions of pure enantiomers [79]. Chromatographic techniques based on chiral stationary phases have been extensively used to separate and acquire the enantiopure compounds. Thus, it should be interesting and significant to explore the promising applications of COFs as chiral stationary phase for the separation of enantiomers. As discussed above, Yan and co-workers [72] have developed several chiral COF-bound capillary columns via an in situ growth approach for chiral capillary GC separation. The chiral COF-based stationary phases show weak dispersion forces and moderate electron donor and acceptor ability as well as part of dipolar and acidic character. These chiral COFbound capillary columns present high resolution for the separation of (±)-1-phenylethanol, (±)-1-phenyl-1-propanol, (±)methyl lactate, and (±)-limonene, which can be effectively separated within 5 min under excellent repeatability and reproducibility. More interestingly, (+)-diacetyl-L-tartaric an-

   Schematic Figure 6        representation for the asymmetric catalysis by chiral COFs. Reprinted with permission from Ref. [74], Copyright 2016 the American Chemical Society (color online).

hydride-functionalized capillary column as the control group was found no chiral separation, indicating that the chiral separation mainly occurs inside the pore of the chiral COFs.

4   Summary and outlook Chiral porous materials are of particular interest because of the increasing demand of materials for asymmetric catalysis and separation as well as for better understanding fundamental aspects in chirality. In this mini review, we focused on recent noteworthy strategies to construct chiral COFs and their potential applications in the field of asymmetric catalysis and chiral separation. COFs are 2D crystalline frameworks with 3D networks and permanently ordered channels. The channels located in COFs are collectively resulted from covalent condensation and layer-by-layer structural stacking. Table 1 shows the BET surface area, pore sizes, and stability of some chiral COFs for catalysis. With the help of synthetic strategies, several highly stable crystalline chiral COFs have been carefully customized. However, there are still severe barriers against the facile fabrication of newly developed chiral COFs. Especially for the chiral COFs constructed by bottom-up strategy, they have to meet simultaneously the requirements for the symmetry of crystallinity and the asymmetry of chiral functionalization. Based on reticular synthesis, symmetric structures are most likely to form when high-symmetry building blocks are used. In comparison with other porous materials like silica and carbon, COFs show a great potential in heterogeneous catalysis because of their structural regularity. For example, COFs could be employed to not only incorporate catalytic species in the porous channels [69], but also covalently embed catalytically active sites in the skeleton [74] as well as anchor catalytic species on the wall of channels [73]. Furthermore, the density of catalytic sites in COFs can be systematically designed and controllably synthesized via the structural engineering methodology [71,76]. In addition, the intrinsic chirality endows chiral COFs with a promising capability for asymmetric organic catalysis. COF-based catalysts have not been utilized to catalyze industrial reactions so far. However, some useful reactions such as Suzuki-Miyaura coupling reaction [69] could be achieved by COF-based catalysts for potential industrial applications. Thus, the future direction of research efforts in this field is to rationally design chiral building blocks and endow 2D/3D chiral COFs with tunability in compositions and topological structures for adapting the applications in chiral recognition and sensing, separation, and heterogeneous catalysis. Although just several chiral COFs have been developed and applied in the asymmetric catalysis and separation, it is expected that these pioneered strategies and applications will pave a promising way for fabricating highly stable chiral COFs toward industrial and commercial applications.

 

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    This Acknowledgments          work was supported by the Singapore Academic Research Fund (RG112/15, RG19/16). 32     The authors declare that they have no conflict of Conflict of interest      interest. 1 2 3 4

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Côté AP, Benin AI, Ockwig NW, O'Keeffe M, Matzger AJ, Yaghi OM. Science, 2005, 310: 1166–1170 Hunt JR, Doonan CJ, LeVangie JD, Côté AP, Yaghi OM. J Am Chem Soc, 2008, 130: 11872–11873 Wan S, Guo J, Kim J, Ihee H, Jiang D. Angew Chem Int Ed, 2008, 47: 8826–8830 Liu Y, Ma Y, Zhao Y, Sun X, Gándara F, Furukawa H, Liu Z, Zhu H, Zhu C, Suenaga K, Oleynikov P, Alshammari AS, Zhang X, Terasaki O, Yaghi OM. Science, 2016, 351: 365–369 El-Kaderi HM, Hunt JR, Mendoza-Cortés JL, Côté AP, Taylor RE, O'Keeffe M, Yaghi OM. Science, 2007, 316: 268–272 Han SS, Mendoza-Cortés JL, Goddard III WA. Chem Soc Rev, 2009, 38: 1460–1476 Feng X, Ding X, Jiang D. Chem Soc Rev, 2012, 41: 6010–6022 Ding SY, Wang W. Chem Soc Rev, 2013, 42: 548–568 Waller PJ, Gándara F, Yaghi OM. Acc Chem Res, 2015, 48: 3053–3063 Sakaushi K, Antonietti M. Acc Chem Res, 2015, 48: 1591–1600 Das S, Heasman P, Ben T, Qiu S. Chem Rev, 2017, 117: 1515–1563 Diercks CS, Yaghi OM. Science, 2017, 355: eaal1585 Xiang Z, Cao D, Dai L. Polym Chem, 2015, 6: 1896–1911 Huang N, Wang P, Jiang D. Nat Rev Mater, 2016, 1: 16068 Segura JL, Mancheño MJ, Zamora F. Chem Soc Rev, 2016, 45: 5635–5671 Li Z, Feng X, Zou Y, Zhang Y, Xia H, Liu X, Mu Y. Chem Commun, 2014, 50: 13825–13828 Huang N, Chen X, Krishna R, Jiang D. Angew Chem Int Ed, 2015, 54: 2986–2990 Xiang Z, Mercado R, Huck JM, Wang H, Guo Z, Wang W, Cao D, Haranczyk M, Smit B. J Am Chem Soc, 2015, 137: 13301–13307 Wei H, Chai S, Hu N, Yang Z, Wei L, Wang L. Chem Commun, 2015, 51: 12178–12181 Stegbauer L, Hahn MW, Jentys A, Savasci G, Ochsenfeld C, Lercher JA, Lotsch BV. Chem Mater, 2015, 27: 7874–7881 Pyles DA, Crowe JW, Baldwin LA, McGrier PL. ACS Macro Lett, 2016, 5: 1055–1058 Baldwin LA, Crowe JW, Pyles DA, McGrier PL. J Am Chem Soc, 2016, 138: 15134–15137 Zeng Y, Zou R, Zhao Y. Adv Mater, 2016, 28: 2855–2873 Kang Z, Peng Y, Qian Y, Yuan D, Addicoat MA, Heine T, Hu Z, Tee L, Guo Z, Zhao D. Chem Mater, 2016, 28: 1277–1285 Fu J, Das S, Xing G, Ben T, Valtchev V, Qiu S. J Am Chem Soc, 2016, 138: 7673–7680 Biswal BP, Chaudhari HD, Banerjee R, Kharul UK. Chem Eur J, 2016, 22: 4695–4699 Pachfule P, Kandambeth S, Díaz Díaz D, Banerjee R. Chem Commun, 2014, 50: 3169–3172 Fang Q, Gu S, Zheng J, Zhuang Z, Qiu S, Yan Y. Angew Chem Int Ed, 2014, 53: 2878–2882 Shinde DB, Kandambeth S, Pachfule P, Kumar RR, Banerjee R. Chem Commun, 2015, 51: 310–313 Xu F, Xu H, Chen X, Wu D, Wu Y, Liu H, Gu C, Fu R, Jiang D. Angew Chem Int Ed, 2015, 54: 6814–6818 DeBlase CR, Hernández-Burgos K, Rotter JM, Fortman DJ, dos S.

33 34

35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56

57

58 59 60

7

Abreu D, Timm RA, Diógenes ICN, Kubota LT, Abruña HD, Dichtel WR. Angew Chem Int Ed, 2015, 54: 13225–13229 Liao H, Wang H, Ding H, Meng X, Xu H, Wang B, Ai X, Wang C. J Mater Chem A, 2016, 4: 7416–7421 Yoo JT, Cho SJ, Jung GY, Kim SH, Choi KH, Kim JH, Lee CK, Kwak SK, Lee SY. Nano Lett, 2016, 16: 3292–3300 Vazquez-Molina DA, Mohammad-Pour GS, Lee C, Logan MW, Duan X, Harper JK, Uribe-Romo FJ. J Am Chem Soc, 2016, 138: 9767–9770 Patra BC, Khilari S, Satyanarayana L, Pradhan D, Bhaumik A. Chem Commun, 2016, 52: 7592–7595 Bai L, Gao Q, Zhao Y. J Mater Chem A, 2016, 4: 14106–14110 Chandra S, Roy Chowdhury D, Addicoat M, Heine T, Paul A, Banerjee R. Chem Mater, 2017, 29: 2074–2080 Ding SY, Dong M, Wang YW, Chen YT, Wang HZ, Su CY, Wang W. J Am Chem Soc, 2016, 138: 3031–3037 Aiyappa HB, Thote J, Shinde DB, Banerjee R, Kurungot S. Chem Mater, 2016, 28: 4375–4379 Huang N, Zhai L, Xu H, Jiang D. J Am Chem Soc, 2017, 139: 2428–2434 Sun Q, Aguila B, Perman J, Earl LD, Abney CW, Cheng Y, Wei H, Nguyen N, Wojtas L, Ma S. J Am Chem Soc, 2017, 139: 2786–2793 Thote J, Aiyappa HB, Deshpande A, Díaz Díaz D, Kurungot S, Banerjee R. Chem Eur J, 2014, 20: 15961–15965 Stegbauer L, Schwinghammer K, Lotsch BV. Chem Sci, 2014, 5: 2789–2793 Vyas VS, Haase F, Stegbauer L, Savasci G, Podjaski F, Ochsenfeld C, Lotsch BV. Nat Commun, 2015, 6: 8508 Dalapati S, Jin E, Addicoat M, Heine T, Jiang D. J Am Chem Soc, 2016, 138: 5797–5800 Lin G, Ding H, Yuan D, Wang B, Wang C. J Am Chem Soc, 2016, 138: 3302–3305 Wang P, Kang M, Sun S, Liu Q, Zhang Z, Fang S. Chin J Chem, 2014, 32: 838–843 Das G, Biswal BP, Kandambeth S, Venkatesh V, Kaur G, Addicoat M, Heine T, Verma S, Banerjee R. Chem Sci, 2015, 6: 3931–3939 Li Z, Zhang Y, Xia H, Mu Y, Liu X. Chem Commun, 2016, 52: 6613–6616 Karmakar A, Kumar A, Chaudhari AK, Samanta P, Desai AV, Krishna R, Ghosh SK. Chem Eur J, 2016, 22: 4931–4937 Zhang Y, Shen X, Feng X, Xia H, Mu Y, Liu X. Chem Commun, 2016, 52: 11088–11091 Chen L, Furukawa K, Gao J, Nagai A, Nakamura T, Dong Y, Jiang D. J Am Chem Soc, 2014, 136: 9806–9809 Dogru M, Bein T. Chem Commun, 2014, 50: 5531–5546 Ding H, Li Y, Hu H, Sun Y, Wang J, Wang C, Wang C, Zhang G, Wang B, Xu W, Zhang D. Chem Eur J, 2014, 20: 14614–14618 Chandra S, Kundu T, Kandambeth S, Babarao R, Marathe Y, Kunjir SM, Banerjee R. J Am Chem Soc, 2014, 136: 6570–6573 Calik M, Auras F, Salonen LM, Bader K, Grill I, Handloser M, Medina DD, Dogru M, Löbermann F, Trauner D, Hartschuh A, Bein T. J Am Chem Soc, 2014, 136: 17802–17807 Cai SL, Zhang YB, Pun AB, He B, Yang J, Toma FM, Sharp ID, Yaghi OM, Fan J, Zheng SR, Zhang WG, Liu Y. Chem Sci, 2014, 5: 4693–4700 Jin S, Supur M, Addicoat M, Furukawa K, Chen L, Nakamura T, Fukuzumi S, Irle S, Jiang D. J Am Chem Soc, 2015, 137: 7817–7827 Ma H, Liu B, Li B, Zhang L, Li YG, Tan HQ, Zang HY, Zhu G. J Am Chem Soc, 2016, 138: 5897–5903 Xu H, Tao S, Jiang D. Nat Mater, 2016, 15: 722–726

8 61 62 63 64

65 66 67 68 69

 

   Sci China Chem   

Liu et al.

Chandra S, Kundu T, Dey K, Addicoat M, Heine T, Banerjee R. Chem Mater, 2016, 28: 1489–1494 Medina DD, Petrus ML, Jumabekov AN, Margraf JT, Weinberger S, Rotter JM, Clark T, Bein T. ACS Nano, 2017, 11: 2706–2713 Meng X, Wang HN, Song SY, Zhang HJ. Chem Soc Rev, 2017, 46: 464–480 Feldblyum JI, McCreery CH, Andrews SC, Kurosawa T, Santos EJG, Duong V, Fang L, Ayzner AL, Bao Z. Chem Commun, 2015, 51: 13894–13897 Fang Q, Wang J, Gu S, Kaspar RB, Zhuang Z, Zheng J, Guo H, Qiu S, Yan Y. J Am Chem Soc, 2015, 137: 8352–8355 Bai L, Phua SZF, Lim WQ, Jana A, Luo Z, Tham HP, Zhao L, Gao Q, Zhao Y. Chem Commun, 2016, 52: 4128–4131 Vyas VS, Vishwakarma M, Moudrakovski I, Haase F, Savasci G, Ochsenfeld C, Spatz JP, Lotsch BV. Adv Mater, 2016, 28: 8749–8754 Tan J, Namuangruk S, Kong W, Kungwan N, Guo J, Wang C. Angew Chem Int Ed, 2016, 55: 13979–13984 Ding SY, Gao J, Wang Q, Zhang Y, Song WG, Su CY, Wang W. J Am Chem Soc, 2011, 133: 19816–19822

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Nagai A, Guo Z, Feng X, Jin S, Chen X, Ding X, Jiang D. Nat Commun, 2011, 2: 536 Xu H, Chen X, Gao J, Lin J, Addicoat M, Irle S, Jiang D. Chem Commun, 2014, 50: 1292–1294 Qian HL, Yang CX, Yan XP. Nat Commun, 2016, 7: 12104 Xu HS, Ding SY, An WK, Wu H, Wang W. J Am Chem Soc, 2016, 138: 11489–11492 Wang X, Han X, Zhang J, Wu X, Liu Y, Cui Y. J Am Chem Soc, 2016, 138: 12332–12335 Ascherl L, Sick T, Margraf JT, Lapidus SH, Calik M, Hettstedt C, Karaghiosoff K, Döblinger M, Clark T, Chapman KW, Auras F, Bein T. Nat Chem, 2016, 8: 310–316 Xu H, Gao J, Jiang D. Nat Chem, 2015, 7: 905–912 Yang CX, Liu C, Cao YM, Yan XP. Chem Commun, 2015, 51: 12254–12257 Liu LH, Yang CX, Yan XP. J Chromatogr A, 2017, 1479: 137–144 Liu GF, Zhang D, Feng CL. Angew Chem Int Ed, 2014, 53: 7789–7793