Post-Synthetic Modification of Nonporous Adaptive Crystals of Pillar[4

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Post-Synthetic Modification of Nonporous Adaptive Crystals of Pillar[4]arene[1]quinone by Capturing Vaporized Amines Errui Li, Kecheng Jie, Yujuan Zhou, Run Zhao, and Feihe Huang J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.8b10192 • Publication Date (Web): 16 Oct 2018 Downloaded from http://pubs.acs.org on October 17, 2018

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Journal of the American Chemical Society

Post-Synthetic Modification of Nonporous Adaptive Crystals of Pillar[4]arene[1]quinone by Capturing Vaporized Amines Errui Li, Kecheng Jie, Yujuan Zhou, Run Zhao, and Feihe Huang State Key Laboratory of Chemical Engineering, Center for Chemistry of High-Performance & Novel Materials, Department of Chemistry, Zhejiang University, Hangzhou 310027, P. R. China; Fax and Tel: +86-571-8795-3189; Email: [email protected]; [email protected] ABSTRACT: Post-synthetic modification in crystalline solids without disruption of crystallinity is very important for exerting control that is unattainable over chemical transformation in solution. This has been achieved in porous crystalline frameworks via solid-solution reactions to endow them with multiple functions. However, this is rather rare in nonporous molecular crystals, especially via solid-vapor reactions. Herein, we report unique solid-vapor post-synthetic modification of nonporous adaptive crystals (NACs) of a pillar[4]arene[1]quinone (EtP4Q1) containing four inert 1,4-diethoxybenzene units and one active benzoquinone unit. Amine vapors that can be physically adsorbed by EtP4Q1 NACs react with the EtP4Q1 backbone via Michael addition with in situ formation of new crystal structures. First, amines are physically adsorbed into cavities of EtP4Q1 molecules and slowly react due to their juxtapsition with the benzoquinone units. Amines that are too bulky to enter EtP4Q1 NACs do not react. Moreover, the process displays both reactant-size and -shape selectivities because of the rigid cavity of EtP4Q1 and the different binding strengths of various amines with EtP4Q1.

1. INTRODUCTION Post-synthetic modification in crystalline solids without disruption of crystallinity is very important for applications ranging from pharmaceuticals to energy and transport such as gas storage and catalysis.1 Very common cases are post-synthetic modifications of porous crystalline frameworks such as metalorganic frameworks (MOFs) and covalentorganic frameworks (COFs) whose crystallinity and rigid pore structures remain after post-synthetic modifications.2,3 These have been realized by reactants entering accessible pores to react with active moieties. The task-specific post-synthetic modification in these porous crystals has led to various targeted applications, such as offering binding sites for specific guests, providing active groups for catalysis, narrowing pore sizes, or altering pore shapes for demanding gas separations, etc.2,3 However, such post-synthetic modification without disruption of crystallinity has been rarely reported in porous molecular crystals.4 Since porous molecular crystals are soluble in common organic solvents, a typical post-synthetic modification of porous molecules often takes place in a homogeneous solution where reactants and porous molecules are dissolved, thus destroying their initial crystallinity and porosity. A solid-vapor reaction in porous molecular crystals might be a solution to retain the initial crystallinity. However, post-synthetic modifications in either porous crystalline frameworks or porous organic crystals via solid-vapor reactions have been rarely reported.5 The major concern is that most organic reactions in a solid-vapor phase are not efficient. Moreover, most of the reactants are not easy to vaporize, which is an inherent challenge for such reactions. The post-synthetic modification of nonporous molecular crystals are even more difficult. The loss of accessible pores in

nonporous crystals drives reactants away from reactive groups inside these crystals. There have been very limited reports about solid-vapor reactions within nonporous crystals via bond-breaking and forming steps to transport reactants.6 The past decade has witnessed the development of pillararenes as a new class of supramolecular macrocyclic hosts.7 Their rigid and symmetrical structures, as well as their easy functionalization,8 further broaden their hostguest properties and applications.9 Our group has pioneered research on pillararene-based nonporous adaptive crystals (NACs).10 NACs are nonporous in the initial crystalline state, but preferred guest vapors induce intrinsic porosity with various sizes and shapes, along with crystal structural transformations. Upon removal of guest molecules, the crystal structure transforms back to the original nonporous state. This unique behavior has been applied in the adsorption of hazardous volatile species and the separation of important hydrocarbon feedstocks.10 On the basis of their unique adaptive behavior, pillararene-based NACs might be ideal candidates for post-synthetic modification with preservation of crystallinity due to the appearance of accessible pores upon guest capture. Herein, we report a unique solid-vapor post-synthetic modification in NACs of a pillar[4]arene[1]quinone (EtP4Q1) containing four inert 1,4-diethoxybenzene units and one reactive benzoquinone unit (Scheme 1). Vapors of aliphatic amines, including propylamine (C3N), butanamine (C4N), pentylamine (C5N), 1,4-butanediamine (C4N2), isoamylamine (isoC5N) and cyclopentylamine (cyC5N), are physically adsorbed and chemically attached to EtP4Q1 NACs with in situ formation of new crystal structures. The post-synthetic modification entirely depends on the physical adsorption procedure. First, amine molecules are physically adsorbed into the cavities of EtP4Q1 molecules; then these

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amines slowly react via efficient Michael addition due to their juxtaposition with the benzoquinone units (Scheme 1c). Amines that are too bulky to enter EtP4Q1 NACs such as cyclohexylamine (cyC6N) do not react with EtP4Q1 NACs. It is worth mentioning that neither the process nor the reaction itself have been reported for pillararenes. Moreover, the process displays both reactant-size and -shape selectivities because of the rigid cavity of EtP4Q1 and the different binding strengths of various amines with EtP4Q1.

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We first obtained a series of single crystals by slow evaporation of linear alkylamine solutions of EtP4Q1. In the crystal structure of C3N-loaded ‘EtP4Q1’ (C3N@EtP4Q1-2C3N), one C3N molecule is encapsulated in the cavity of the macrocycle, forming a [2]pseudorotaxane (Figure 1a). Intriguingly, two C3N molecules are directly attached to the ortho position of carbonyl groups on the benzoquinone unit. This crystal structure also revealed that during the crystal growth, not only supramolecular complexation but also chemical reactions between EtP4Q1 and C3N took place, thus generating a new pillar[5]arene derivative EtP4Q1-2C3N. In addition, three hydrogen atoms on C3N have CH/π interactions with the arene units of EtP4Q1-2C3N. The distances are between 2.779 and 3.009 Å, shorter than the longest interatomic distance in a CH/π interaction (3.05 Å) (Figure 1a).9a In the packing mode, C3N@EtP4Q1-2C3N assembles into slip-stacked structures (Figure 1a and S4). Similarly, in the crystal structure of C4Nor C5N-loaded ‘EtP4Q1’ (C4N@EtP4Q1-2C4N or C5N@EtP4Q1-2C5N), one C4N or C5N molecule is encapsulated in the cavity of EtP4Q1-2C4N or EtP4Q1-2C5N with two C4N or C5N molecules chemically-attached to the EtP4Q1 backbone, forming a [2]pseudorotaxane. The encapsulated guest molecules are also stabilized by multiple CH/π interactions (Figure 1b and 1c). Different from EtP4Q1-2C3N structure, each EtP4Q1-2C4N or EtP4Q1-2C5N molecule is parallel to adjcant molecules to form one-dimensional channel structures. The hydrogen bonding interactions between two adjacent one-dimensional channels further stabilize them (Figure S5 and S6). The success of in situ solution growth of linear alkylamine-appended EtP4Q1 crystals motivated us to investigate the possibility of linear alkanediamines, which may be beneficial for the further modification of pillararenes.12 In the same way, single crystals of C4N2-appended EtP4Q1 were obtained by slow evaporation of an EtP4Q1 butanediamine solution. In the crystal structure, two C4N2 molecules have been introduced at the ortho positions of carbonyl groups on the benzoquinone unit of EtP4Q1 to generate new product EtP4Q1-2C4N2. Meawhile, one C4N2 molecule is physically encapsulated in the cavity, forming a [2]pseudorotaxane (C4N2@EtP4Q1-2C4N2) (Figure 1d). It is worth mentioning that each EtP4Q1-2C4N2 molecule has an unreacted amine group on both rims, which provides active sites for further modifications. In addition, four hydrogen atoms on C4N2 have CH/π interactions with the arene units of EtP4Q1-2C4N2. Unlike the structure of C4N@EtP4Q1-2C4N, C4N2@EtP4Q1-2C4N2 has hydrogen bonding between two adjacent C4N2@EtP4Q1-2C4N2 complexes besides interchannel hydrogen bonding interactions, which may further stabilize the structure (Figure S7).

Scheme 1. (a) Chemical structure of EtP4Q1. (b) Chemical reaction of benzoquinone and amines through Michael addition. (c) Schematic representation of the attachment of amines to nonporous EtP4Q1 crystals.

2. RESULTS AND DISCUSSION In situ solution growth of alkylamine-appended EtP4Q1 crystals. It has been reported that 1,4-benzoquinone undergoes the Michael addition reaction with aliphatic amines or aromatic amines to selectively afford 2,5-bis(alkyl/arylamino)-1,4-benzoquinones in solution under aerobic conditions (Scheme 1b).11 We assumed that the incorporation of a benzoquinone unit into the macrocyclic backbone of pillararenes would make it possible to post-synthetically modify the pillararenes through the reaction of the benzoquinone unit with aliphatic amines in solution. According to a previously published procedure, EtP4Q1, which contains four inert 1,4-diethoxybenzene units and one active benzoquinone unit, was synthesized by partial oxidation of EtP5 with ammonium cerium nitrate in a mixture of tetrahydrofuran and water.8a Due to the good solubility of EtP4Q1 in different aliphatic amines, single crystals of alkylamine-appended EtP4Q1 were successfully obtained by an in situ solution growth method.

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Figure 1. Single crystal structures: (a) C3N@EtP4Q1-2C3N; (b) C4N@EtP4Q1-2C4N; (c) C5N@EtP4Q1-2C5N; (d) C4N2@EtP4Q1-2C4N2; (e) isoC5N@EtP4Q1-2isoC5N. In the single crystal structures: C gray, O red, H white; Certain H atoms are omitted for clarity.

It has been previously reported that branched alkanes can not be encapsulated in the cavity of pillar[5]arene either in solution or in the solid state due to the cavity-size limitation of pillar[5]arene (ca. 4.7 Å).10a We deduced that only two molecules of branched alkylamine would be chemically-appended on EtP4Q1 without physical encapsulation. With this deduction, we obtained single crystals of isoC5N-appended EtP4Q1 by slow evaporation of an EtP4Q1 isoamylamine solution. To our surprise, the resultant single crystal structure possesses structure similar to that obtained from linear alkylamines. In the crystal structure, two isoC5N molecules are attached to the ortho positions of the benzoquinone unit to generate EtP4Q1-2isoC5N (Figure 1e). Unexpectedly, one isoC5N molecule is encapsulated in its cavity, forming a [2]pseudorotaxane (isoC5N@EtP4Q1-2isoC5N). From the top view, side view and packing mode of isoC5N@EtP4Q1-2isoC5N (Figure 1e and S8), the skeleton of the macrocyclic host is not significantly distorted with the branched guest in its cavity. It is worth mentioning that there are rare reports about the solid state structures of complexes of pillar[5]arene or its derivatives with branched aliphatic compounds.710 In addition, five hydrogen atoms on isoC5N have CH/π interactions with the arene units of EtP4Q1-2isoC5N. Likewise, hydrogen

bonding interactions exist between adjacent EtP4Q1-2isoC5N molecules to form parallel one-dimensional channels, even though their cavities are penetrated by relatively bulky isoC5N molecules (Figure S8). Single-component solid-vapor post-synthetic modification experiments. The effecient in situ solution growth of amine-appended EtP4Q1 crystals prompted us to consider the possibility of in situ solid-vapor post-synthetic modification of desolvated EtP4Q1 crystals. To do so, we activated as-synthesized EtP4Q1 in vacuo at 100 °C overnight to afford desolvated EtP4Q1. It was confirmed by powder X-ray diffraction (PXRD) to be crystalline (referred to as EtP4Q1α, Figure S2). N2 sorption experiments showed the nonporous nature of EtP4Q1α (Figure S3). To test the possibility of solid-vapor post-synthetic modification, we exposed EtP4Q1α crystals to different aliphatic amine vapors at room temperature. Interestingly, vapochromic phenomena occurred during the adsorption. Upon exposure to aliphatic amine vapors, the color of the crystals gradually changed. It took one or two days to complete the color changes from dark red to black, dark purple, gray, or wine (Figure 2a). These phenomena were followed by diffuse reflectance spectroscopy (Figure 2b). After exposure to different aliphatic amines, the absorption bands in the crystals



at 600–700 nm increased in intensity. Among them, the slight color difference between EtP4Q1α and EtP4Q1α after adsorption of cyC5N or cyC6N was reflected in the proximity of their absorption bands.

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are direct demonstrations of the successful solid-vapor attachment of the aliphatic amines to the EtP4Q1 macrocyclic skeleton with crystal structural transformations, resulting in the color changes.

Figure 2. (a) Photographs showing color changes when 25 mg of EtP4Q1α crystals were exposed to aliphatic amine vapors. (b) Diffuse reflectance spectra of EtP4Q1α crystals (black line) and crystals after exposure to C3N (red line), C4N (blue line), C5N (green line), C4N2 (magenta line), isoC5N (dark yellow line), cyC5N (navy line), and cyC6N (brown line) vapors.

Figure 3. PXRD patterns of EtP4Q1: (I) EtP4Q1α; (II) EtP4Q1α after adsorption of C3N; (III) simulated from single crystal structure of C3N@EtP4Q1-2C3N; (IV) EtP4Q1α after adsorption of C4N; (V) simulated from single crystal structure of C4N@EtP4Q1-2C4N; (VI) EtP4Q1α after adsorption of C5N; (VII) simulated from single crystal structure of C5N@EtP4Q1-2C5N; (VIII) EtP4Q1α after adsorption of C4N2; (IX) simulated from single crystal structure of C4N2@EtP4Q1-2C4N2; (X) EtP4Q1α after adsorption of isoC5N; (XI) simulated from single crystal structure of isoC5N@EtP4Q12isoC5N.

The mechanism behind the color changes was studied by 1H NMR, Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and PXRD experiments. 1H NMR spectra showed that one EtP4Q1 molecule could physically capture nearly one aliphatic amine molecule despite the nonporosity of EtP4Q1α. Meanwhile, all the 1H NMR spectra of the host molecules underwent some changes (Figure S9S20). Especially, the original Ar-H signals of EtP4Q1 disappeared and some new Ar-H signals appeared, indicating chemical transformations of EtP4Q1. FT-IR spectra revealed new peaks at 33603250 cm1, representing the amino stretching vibration (Figure S21), confirming the capture of amines. The TGA results also confirmed the quantitative physical adsorption and chemical adsorption processes. There was a weight loss of one aliphatic amine molecule at 100 C and 200 C, respectively, representing the physical desorption and chemical desorption processes (Figure S22). PXRD experiments were carried out to monitor the structural transformations. En masse, the PXRD patterns of EtP4Q1α after adsorption of C3N, C4N, C5N, C4N2 or isoC5N were different from EtP4Q1α and in good agreement with the simulated patterns from single crystal structures of C3N@EtP4Q1-2C3N, C4N@EtP4Q1-2C4N, C5N@EtP4Q1-2C5N, C4N2@EtP4Q1-2C4N2, and isoC5N@EtP4Q1-2isoC5N, respectively (Figure 3 and S23S27). Hence, the adsorption of these amines by EtP4Q1α triggers a crystal transformation from EtP4Q1α to C3N@EtP4Q1-2C3N, C4N@EtP4Q1-2C4N, C5N@EtP4Q1-2C5N, C4N2@EtP4Q1-2C4N2, and isoC5N@EtP4Q1-2isoC5N, respectively. The above results

In order to reveal the mechanism, C4N was chosen as a model amine. Time-dependent solid-vapor adsorption experiments showed that the color of EtP4Q1α crystals gradually changed from dark red to dark purple when they were exposed to C4N vapor (Figure 4a). Time-dependent 1H NMR spectra were gathered (Figure 4b). In the first 12 h, proton signals related to EtP4Q1 were almost unchanged, while proton signals corresponding to C4N started to appear. This indicated a pure physical adsorption process of C4N in EtP4Q1α at the beginning. Afterwards, a new Ar-H proton signal appeared at 6.86 ppm and gradually strengthened, accompanied by weakening of the original Ar-H signals of EtP4Q1. This revealed the chemical reaction of C4N with EtP4Q1. Eventually, EtP4Q1 was converted into a new compound, EtP4Q1-2C4N. The C4N vapor sorption isotherm was also obtained. As can be seen from Figure 4c, the adsorption of C4N vapor by EtP4Q1α occured at a certain pressure (P/P0 = 0.2), indicating a gate-opening behavior for the physical adsorption. Chemical adsorption started at a higher pressure (P/P0 = 0.6) after physical adsorption was finished. It is worth mentioning that a large amount of C4N can not be released even at reduced pressure, indicating the stable storage of C4N in EtP4Q1α. The amount of the unreleased C4N was caculated to be 3


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Journal of the American Chemical Society Based on the above mentioned results of time-dependent 1H NMR, PXRD, and vapor sorption isotherm experiments (Figure 4, bdc), the overall mechanism can be explained as follows: when nonporous EtP4Q1α crystals were exposed to C4N vapor, the inherent ‘pores’ of EtP4Q1 were induced to accommodate C4N, along with a crystal structural transformation from EtP4Q1α to C4N@EtP4Q1; afterwards, C4N molecules encapsulated in the cavities of EtP4Q1 molecules slowly reacted with the macrocycles due to the juxtaposition between amines and benzoquinone units. The mono-modified hosts with empty cavities continued to capture C4N into their cavities for another modifcation, which was confirmed by mass spectrometric peaks related to the mono-modified host (Figure S29 and S30). When both physical adsorption and chemical modifications were finished, EtP4Q1α was completely transformed into C4N@EtP4Q1-2C4N.

times the amount of physically-adsorbed C4N, which may be due to the formation of C4N@EtP4Q1-2C4N. The chemical bonds between chemically-adsorbed C4N and EtP4Q1 are stable enough for the storage, while the stable physical storage of C4N in the cavities of EtP4Q1-2C4N can be ascribed to the multiple CH/ interactions between C4N and EtP4Q1-2C4N. Time-dependent PXRD experiments were performed to verify the structural changes during the adsorption process (Figure 4d). The crystal structure of EtP4Q1α started to change instantly upon exposure to C4N vapor. A phase transition was completed after 12 h, a time when the physical adsorption process came to an end as demonstrated by the time-dependent 1H NMR experiment. The structure at this time was EtP4Q1 physically-loaded with C4N (referred to as C4N@EtP4Q1). Another phase transition started afterwards and was finished in the end, indicating the complete transformation from EtP4Q1α to C4N@EtP4Q1-2C4N.

Figure 4. (a) Photographs showing time-dependent color changes of EtP4Q1α upon uptake of C4N. (b) Time-dependent 1H NMR spectra (500 MHz, CDCl3, 298 K) of EtP4Q1α upon exposure to C4N vapor. (c) Vapor sorption isotherm of EtP4Q1α towards C4N. Solid symbols: adsorption; open symbols: desorption. (d) Time-dependent PXRD patterns of EtP4Q1α upon exposure to C4N vapor. (e) Schematic representation of the post-synthetic modification in EtP4Q1α by capturing C4N vapor.

To confirm our inferences, cyclic alkylamines including cyC5N and cyC6N, which might be too bulky to enter the cavity of EtP4Q1, were employed. However, some

characterizations suggested that cyC5N was successfully attached to EtP4Q1 while cyC6N was not. Upon exposure to cyC5N vapor, the 1H NMR spectrum of EtP4Q1α showed a



significant change, indicating that chemical reactions on EtP4Q1α took place (Figure 5a and S31). A 2D NOSEY experiment was carried out to confirm the encapsulation of cyC5N in EtP4Q1-2cyC5N. NOE correlation signals were expressly observed between the peaks of protons H1 and H2 of cyC5N and those of proton Hd on EtP4Q1-2cyC5N (Figure S32), indicating that cyC5N was encapsulated into the cavity of EtP4Q1-2cyC5N in solution. Since the single crystal structure of cyC5N-appended EtP4Q1 was not obtained by the in situ solution growth method, we dissolved in situ solid-vapor post-synthetic cyC5N-appended EtP4Q1 crystals in methanol and got a preliminary single crystal structure of EtP4Q1-2cyC5N by slow evaporation (Figure S33). Meanwhile, the PXRD patterns showed that the post-synthetic modification induced a crystal structural transformation to a new structure, which is in good agreement with the simulated PXRD pattern from the single crystal structure of EtP4Q1-2cyC5N (Figure S34). We concluded that the successful attachment of cyC5N to EtP4Q1 depends on the suitable cavity size of EtP4Q1 for cyC5N. However, the results obtained for cyC6N are quite different. When EtP4Q1α was exposed to cyC6N vapor for 48 h, no reaction occured as confirmed by 1H NMR (Figure 5c and S35). Whereas EtP4Q1α was dissolved in the cyC6N solution, the 1H NMR spectrum obtained after the solvent was evaporated changed significantly (Figure S36). These phenomena on the other hand confirmed the solid-vapor post-synthetic modification mechanism: In the solution phase, cyclohexylamine can react with quinone units without entering into the cavity due to the presence of excess cyC6N molecules that are close to quinones. In the solid state, cyC6N molecule is too bulky to enter the cavity of EtP4Q1. Hence, the physical adsorption of cyC6N with a gate-opening behavior in EtP4Q1α crystals can not be triggered, thus preventing cyC6N from engaging the reactive benzoquinone sites on EtP4Q1. On the contrary, cyC5N with a smaller molecular size was attached to EtP4Q1 in the same way as linear or branched amines. The above experiments also revealed a reactant size-selectivity of the post-synthetic modification of EtP4Q1α crystals.

modification experiments. Besides the observed reactant size-selectivity, reactant-shape selectivity was also tested. Here, we chose C5 amines with linear, branched and cyclic shapes as model reactants. When EtP4Q1α was exposed to an equimolar mixture of C5N and isoC5N vapors or C5N and cyC5N vapors, the 1H NMR spectra showed that in both cases the final major products were EtP4Q1-2C5N (Figure 6 and S37S38). PXRD experiments confirmed the crystal structural transformation from EtP4Q1α to C5N@EtP4Q1-2C5N (Figure 6a and 6b) for both cases. These results revealed that the post-synthetic modification of EtP4Q1α had a reactant-shape selectivity towards the linear C5 amine. The selectivity was determined by the different binding affinities of EtP4Q1 with linear, branched and cyclic reactants. In the physical adsorption process, EtP4Q1α preferentially adsorbed C5N rather than isoC5N or cyC5N to form C5N@EtP4Q1 due to the higher binding strength between C5N and EtP4Q1. Then C5N molecules encapsulated in the cavities of EtP4Q1 molecules slowly reacted with the macrocycles to form C5N@EtP4Q1-2C5N. Thus, the macrocyclic skeleton plays a crucial role in the reactant sorting process.

Figure 6. (a) PXRD patterns: (I) EtP4Q1α after exposure to C5N; (II) EtP4Q1α after exposure to an equimolar mixture of C5N and isoC5N; (III) EtP4Q1α after exposure to isoC5N. (b) PXRD patterns: (I) EtP4Q1α after exposure to C5N; (II) EtP4Q1α after exposure to an equimolar mixture of C5N and cyC5N; (III) EtP4Q1α after exposure to cyC5N. (c) Schematic representation of the amine-shape-selective post-synthetic modification in EtP4Q1α crystals.

Reversibility of the solid-vapor post-synthetic modification. To test whether the solid-vapor post-synthetic modification was reversible, we heated a sample of C4N@EtP4Q1-2C4N at 110 °C under vacuum for 12 h. However, this treatment only removed the physically-adsorbed C4N, while EtP4Q1-2C4N remained stable according to an 1 H NMR experiment (Figure S39). A PXRD experiment showed that the guest-free EtP4Q1-2C4N sample became amorphous. Upon exposure to C4N vapor, the amorphous EtP4Q1-2C4N sample was transformed back to crystalline C4N@EtP4Q1-2C4N (Figure 7a). Similar phase transitions were also observed for C4N2@EtP4Q1-2C4N2, isoC5N@EtP4Q1-2isoC5N, and cyC5N@EtP4Q1-2cyC5N, respectively (Figure S40S45). This indicated that the physical adsorption process was totally reversible. When

Figure 5. 1H NMR spectra (500 MHz, CDCl3, 298 K): (a) EtP4Q1α after exposure to cyC5N; (b) EtP4Q1α; (c) EtP4Q1α after exposure to cyC6N.

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C4N@EtP4Q1-2C4N was heated in a nitrogen atmosphere at a higher temperature (300 °C), the mass spectrum of the resultant powder showed a peak corresponding to the molecular weight of EtP4Q1-C4N (Figure S46). This result indicated that EtP4Q1-2C4N was decomposed into EtP4Q1-C4N by releasing one post-synthetically modified C4N molecule at the higher temperature. Differential scanning calorimetry (DSC) of C4N@EtP4Q1-2C4N also confirmed the above result (Figure 7b). The broad exothermic peak at 93 C corresponded to the physical loss of C4N. Another broad endothermic peak at 233 C was ascribed to the release of one post-synthetically modified C4N molecule. Meanwhile, the skeleton of pillararene derivative was totally decomposed at 424 C without release of another C4N molecule. Moreover, the TGA analysis agreed well with the DSC result (Figure S22). Thus, only one molecule of chemically attached aliphatic amine can be released before the macrocyclic skeleton is decomposed, indicating the irreversible nature of the post-synthetic modification.

example, the new method avoids further purification procedure, and thus can be used to synthesize pillararene deiveratives that are hard to purify. In the near future, post-synthetically modified pillararene crystals will be designed and synthesized for targeted applications such as organic contaminant removal, toxicant detection, chiral separations, etc.

3. EXPERIMENTAL SECTION Materials. All reagents were commercially available and used as supplied without further purification. According to a previously published procedure, EtP4Q1 was synthesized by partial oxidation of EtP5 with ammonium cerium nitrate in a mixed solution of tetrahydrofuran and water,13 purified by column chromotography, and dried in vacuo at 100 °C overnight to afford the desolvated activated crystalline EtP4Q1α (see details in the Supporting Information). Synthesis of EtP4Q1-2C3N. An open 5 mL vial containing 0.025 g of activated EtP4Q1α crystals was placed in a sealed 20 mL vial containing 2 mL of an n-propylamine solution at room temperature for 24 h. The obtained crystals were exposed to air for 0.5 h to remove the surface-physically adsorbed n-propylamine vapor to provide EtP4Q1-2C3N as black crystals (0.028 g, yield: 95%). 1H NMR (500 MHz, CDCl3, 298 K)  (ppm): 6.86 (s, 2H), 6.686.66 (t, J = 10 Hz, 6H), 3.933.48 (m, 30H), 1.431.15 (m, 28H), 0.69 (s, 6H) (Figure S48). 13C NMR (125 MHz, CDCl3, 298 K)  (ppm): 179.60, 149.35, 148.92, 148.82, 148.28, 146.37, 127.75, 127.45, 127.08, 126.20, 114.22, 114.04, 113.75, 106.41, 76.26, 76.01, 75.75, 63.35, 62.89, 62.81, 62.60, 46.15, 29.44, 29.15, 28.68, 22.55, 14.21, 14.04, 13.83, 13.75, 10.08 (Figure S4). mp 73.174.7 C. FTICRMS: m/z calcd for C57H74O10N2Na [EtP4Q1-2C3N + Na]+: 969.5241, found 969.5211, error 3 ppm. Synthesis of EtP4Q1-2C4N. An open 5 mL vial containing 0.025 g of activated EtP4Q1α crystals was placed in a sealed 20 mL vial containing 2 mL of an n-butylamine solution at room temperature for 24 h. The obtained crystals were exposed to air for 0.5 h to remove the surface-physically adsorbed n-butylamine vapor to provide EtP4Q1-2C4N as dark purple crystals (0.029 g, yield: 97%). 1H NMR (500 MHz, CDCl3, 298 K)  (ppm): 6.86 (s, 2H), 6.66 (s, 6H), 3.933.53 (m, 30H), 1.451.16 (m, 32H), 0.67 (s, 6H) (Figure S49). 13C NMR (125 MHz, CDCl3, 298 K) δ (ppm): 179.57, 149.40, 149.03, 148.75, 148.32, 146.41, 127.65, 127.62, 127.48, 127.00, 126.31, 114.16, 114.04, 113.93, 106.20, 76.27, 76.01, 75.76, 63.36, 62.85, 62.78, 62.69, 44.21, 31.36, 29.20, 29.17, 28.69, 18.78, 14.20, 14.04, 13.81, 13.77, 12.51 (Figure S6). mp 67.869.1 C. FTICRMS: m/z calcd for C59H78O10N2Na [EtP4Q1-2C4N + Na]+: 997.5554, found 997.5533, error 2 ppm. Synthesis of EtP4Q1-2C5N. An open 5 mL vial containing 0.025 g of activated EtP4Q1α crystals was placed in a sealed 20 mL vial containing 2 mL of an n-pentylamine solution at room temperature for 24 h. The obtained crystals were exposed to air for 0.5 h to remove the surface-physically adsorbed n-pentylamine vapor to provide EtP4Q1-2C5N as dark purple crystals (0.029 g, yield: 87%). 1H NMR (500 MHz, CDCl3, 298 K)  (ppm): 6.79 (s, 2H), 6.59 (s, 6H), 3.813.42 (m, 30H), 1.421.08 (m, 36H), 0.62 (s, 6H) (Figure S50). 13C

Figure 7. (a) PXRD patterns: (I) C4N@EtP4Q1-2C4N; (II) C4N@EtP4Q1-2C4N after removal of the physically-adsorbed C4N guest; (III) guest-free EtP4Q1-2C4N after adsorption of C4N. (b) DSC curve of C4N@EtP4Q1-2C4N. (c) Schematic representation of the reversibility of the post-synthetic modification of EtP4Q1α crystals.

Conclusions In summary, we for the first time report a unique solid-vapor post-synthetic modification of NACs of EtP4Q1 by capturing vaporized amines. Amine vapors that can be physically adsorbed by EtP4Q1 NACs can be chemically attached to the EtP4Q1 backbone via Michael addition with concommitant in situ formation of new crystal structures. Each physically adsorbed amine molecule is located in the cavity of EtP4Q1; this amine then slowly reacts due to the juxtaposition with the encapsulated amine molecule and the benzoquinone unit. Amine vapors that are too bulky to enter into EtP4Q1 NACs cannot be chemically attached to EtP4Q1. Moreover, the solid-vapor post-synthetic modification of EtP4Q1 NACs shows both reactant-size and -shape selectivities because of the rigid cavity of EtP4Q1 and the binding strength differences of various amines with EtP4Q1. Moreover, this unique behavior together with modification methods for pillararenes offers plenty of possibilities for future studies. For



NMR (125 MHz, CDCl3, 298 K)  (ppm): 179.47, 149.41, 149.05, 148.76, 148.32, 146.33, 127.67, 127.57, 127.02, 126.37, 114.30, 114.11, 113.93, 105.98, 76.27, 76.02, 75.76, 63.34, 62.80, 62.73, 44.45, 29.29, 29.17, 28.96, 28.69, 27.81, 21.19, 14.19, 14.02, 13.80, 13.77, 12.81 (Figure S8). mp 66.567.9 C. FTICRMS: m/z calcd for C61H83O10N2 [EtP4Q1-2C5N + H]+: 1003.6048, found 1003.6026, error 2 ppm. Synthesis of EtP4Q1-2C4N2. An open 5 mL vial containing 0.025 g of activated EtP4Q1α crystals was placed in a sealed 20 mL vial containing 2 mL of a 1,4-butanediamine solution at room temperature for 48 h. The obtained crystals were exposed to air for 0.5 h to remove the surface-physically adsorbed 1,4-butanediamine vapor to provide EtP4Q1-2C4N2 as gray crystals (0.030 g, yield: 94%). 1H NMR (500 MHz, CDCl3, 298 K)  (ppm): 6.86 (s, 2H), 6.726.68 (d, J = 20 Hz, 6H), 3.943.55 (m, 30H), 2.25 (s, 4H), 1.451.19 (m, 32H) (Figure S51). 13C NMR (125 MHz, CDCl3, 298 K)  (ppm): 179.92, 149.47, 149.15, 149.00, 148.70, 148.22, 127.77, 127.60, 127.16, 126.01, 114.82, 114.30, 114.04, 113.75, 107.43, 63.61, 63.00, 62.88, 62.79, 44.34, 40.29, 29.28, 29.13, 28.89, 28.69, 26.64, 14.27, 14.20, 13.97, 13.93 (Figure S10). mp 96.898.7 C. FTICRMS: m/z calcd for C59H81O10N4 [EtP4Q1-2C4N2 + H]+: 1005.5953, found 1005.5932, error 2 ppm. Synthesis of EtP4Q1-2isoC5N. An open 5 mL vial containing 0.025 g of activated EtP4Q1α crystals was placed in a sealed 20 mL vial containing 2 mL of an isopentylamine solution at room temperature for 24 h. The obtained crystals were exposed to air for 0.5 h to remove the surface-physically adsorbed isopentylamine vapor to provide EtP4Q1-2isoC5N as dark purple crystals (0.030 g, yield: 95%). 1H NMR (500 MHz, CDCl3, 298 K)  (ppm): 6.85 (s, 2H), 6.666.62 (t, J = 20 Hz, 6H), 3.913.48 (m, 30H), 1.451.12 (m, 30H), 0.87 (s, 12H) (Figure S52). 13C NMR (125 MHz, CDCl3, 298 K)  (ppm): 179.32, 149.59, 149.37, 149.09, 148.77, 148.37, 146.04, 127.75, 127.57, 127.47, 127.07, 126.47, 114.19, 114.04, 113.67, 105.67, 76.26, 76.01, 75.76, 63.35, 63.28, 62.86, 62.77, 42.74, 38.11, 29.32, 29.20, 28.80, 28.69, 24.73, 21.44, 14.17, 13.96, 13.76, 13.73 (Figure S12). mp 66.768.7 C. FTICRMS: m/z calcd for C61H82O10N2Na [EtP4Q1-2isoC5N + Na]+: 1025.5867, found 1025.5834, error 3 ppm. Synthesis of EtP4Q1-2cyC5N. An open 5 mL vial containing 0.025 g of activated EtP4Q1α crystals was placed in a sealed 20 mL vial containing 2 mL of a cyclopentylamine solution at room temperature for 24 h. The obtained crystals were exposed to air for 0.5 h to remove the surface-physically adsorbed cyclopentylamine vapor to provide EtP4Q1-2cyC5N as wine colored crystals (0.030 g, yield: 94%). 1H NMR (500 MHz, CDCl3, 298 K)  (ppm): 6.86 (s, 2H), 6.676.62 (t, J = 25 Hz, 6H), 4.53 (s, 2H), 3.923.57 (m, 28H), 1.371.13 (m, 40H) (Figure S53). 13C NMR (125 MHz, CDCl3, 298 K)  (ppm): 179.47, 149.31, 148.93, 148.85, 148.40, 145.45, 127.72, 127.50, 127.09, 126.31, 114.37, 114.08, 113.76, 105.67, 76.25, 76.00, 75.74, 63.35, 62.95, 62.86, 62.60, 54.20, 33.49, 33.17, 29.56, 29.18, 28.68, 23.02, 22.56, 14.23, 13.95, 13.90, 13.72 (Figure S14). mp 82.984.0 C. MALDI-TOF MS: m/z calcd for C61H81O10N2 [EtP4Q1-2cyC5N + H]+: 1001.5891, found 1001.5904, error 2 ppm. Single crystal growth. Single crystals were grown by slow

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evaporation: 5 mg portions of dry EtP4Q1α were transfered into small glass sample vials and dissolved in 2 mL of C3N, C4N, C5N, C4N2 or isoC5N, respectively. The resultant homogenous solutions were allowed to slowly evaporate at room temperature for 57 days to afford dark purple crystals. Aliphatic amine vapor uptake measurements. For each single-component aliphatic amine vapor-phase experiment, an open 5 mL vial containing 20 mg of guest-free EtP4Q1α adsorbent was placed in a sealed 20 mL vial containing 2 mL of an aliphatic amine for 12 days until the color of the crystals completely changed.

ASSOCIATED CONTENT Supporting Information Experimental details and supporting data. This material is available free of charge via the Internet at http://pubs.acs.org. Experimental details, crystallography, and other materials (PDF) X-ray crystallographic data for EtP4Q1·C3N (CIF) X-ray crystallographic data for EtP4Q1·C4N (CIF) X-ray crystallographic data for EtP4Q1·C5N (CIF) X-ray crystallographic data for EtP4Q1·C4N2 (CIF) X-ray crystallographic data for EtP4Q1·iosC5N (CIF)

AUTHOR INFORMATION Corresponding Author [email protected]; [email protected]

Notes The authors declare no competing ﬁnancial interest.

ACKNOWLEDGMENT Here we gratefully acknowledge the National Natural Science Foundation of China (21434005, 91527301) for financial support.

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Post-Synthetic Modification of Nonporous Adaptive Crystals of Pillar[4

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