Bent Anthracene Dimers as Versatile Building Blocks for

Jul 26, 2019 - Conspectus. This Account provides a comprehensive summary of our 1-decade-long investigations into bent anthracene dimers as versatile ...
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Bent Anthracene Dimers as Versatile Building Blocks for Supramolecular Capsules Michito Yoshizawa* and Lorenzo Catti

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Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan CONSPECTUS: This Account provides a comprehensive summary of our 1-decade-long investigations into bent anthracene dimers as versatile building blocks for supramolecular capsules. The investigations initiated in 2008 with the design of an anthracene dimer with a meta-phenylene spacer bearing two substituents on the convex side. Using the bent polyaromatic building block, we began to develop novel supramolecular capsules from two different synthetic approaches. One is a coordination approach, which was pursued by converting the building block into a bent ligand with two pyridine units at the terminal positions. The ligands quantitatively assemble into an M2L4-type capsule through coordination bonding with metal ions. The other is a π-stacking approach, which was followed by utilizing the block as a bent amphiphilic molecule with two trimethylammonium groups at the spacer. In water, the amphiphiles spontaneously assemble into a micelle-type capsule through the hydrophobic effect and π-stacking interactions. Simple modification of the building block allowed us to prepare a wide variety of coordination capsules as well as π-stacking capsules, bearing different hydrophilic side-chains, terminal substitutions, connecting units, polyaromatic panels, or spacer units. The coordination capsule possesses a rigid cavity, with a diameter of ∼1 nm, surrounded by multiple anthracene panels. The spherical polyaromatic cavity binds various synthetic molecules (e.g., paracyclophanes, corannulene, BODIPY, and fullerene C60) in aqueous solutions. With the aid of the polyaromatic shell, photochemically and thermally reactive radical initiators and oligosulfurs are greatly stabilized in the cavity. Biomolecules such as hydrophilic sucrose and oligo(lactic acid)s as well as hydrophobic androgenic hormones are bound by the capsule with high selectivity. In addition, long amphiphilic poly(ethylene oxide)s are threaded into the closed shell of the capsule(s) to generate unusual pseudorotaxane-shaped host−guest complexes in water. In contrast, the π-stacking capsule furnishes a flexible cavity, adaptable to the size and shape of guest molecules, encircled by multiple anthracene panels. In water, the capsule binds hydrophobic fluorescent dyes (e.g., Nile red and DCM) in the cavity. Simple grinding of the bent amphiphile with highly hydrophobic nanocarbons such as fullerenes, nanographenes, and carbon nanotubes (followed by sonication) as well as metal-complexes such as Cu(II)-phthalocyanines and Mn(III)tetraphenylporphyrins leads to the efficient formation of water-soluble host−guest complexes upon encapsulation. Red emission from otherwise water-deactivated Eu(III)-complexes is largely enhanced in water through encapsulation. Moreover, the incorporation of pH- and photoswitches into the amphiphile affords stimuli-responsive π-stacking capsules, capable of releasing bound guests by the addition of acid and light irradiation, respectively, in water. The host functions of the coordination and π-stacking capsules are complementary to each other, which enables selection of the capsule-type depending on the envisioned target. We are convinced that continued investigation of the present supramolecular capsules featuring the bent anthracene dimer and its derivatives will further increase their value as advanced molecular tools for synthetic, analytical, material, biological, and/or medical applications. skeleton. So far, a large quantity of “bent” organic molecules, such as diphenylmethane, meta-diethynylbenzene, metaterphenyl, glycoluril, 9,10-dihydro-9,10-ethanoanthracene, Tröger’s base, and their derivatives (Figure 1), have been employed as useful supramolecular building blocks.2−4 The resultant supramolecular capsules and cages display intriguing molecular binding/recognition abilities as well as unusual physical/chemical phenomena in their cavities, which cannot be observed both in bulk solution and in the solid state without the supramolecular hosts.

1. INTRODUCTION In supramolecular chemistry, in other words, molecular assembly chemistry, the suitable selection or rational design of key building blocks is of prime importance for the synthesis of functional supramolecular architectures.1 One of the reasons is that the properties of the building blocks can be condensed, amplified, or altered upon assembly. Particularly, supramolecular structures of capsular or cagelike fashion can reinforce the effect of the selected building blocks via their inner cavities, in which bound guest molecules effectively interact with multiple building blocks at the same time. Their number, position, and orientation can furthermore often be precisely adjusted through the choice of the suitable capsular or cagelike © XXXX American Chemical Society

Received: June 4, 2019

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3. COORDINATION CAPSULES 3.1. Synthesis, Structure, and Fluorescence

Our first coordination capsule established in 2011 is featuring a highly symmetrical M2L4 structure with a spherical polyaromatic shell (Figure 4a),7 unlike previously reported M2L4 cages composed of wirelike frameworks.8 Norifumi Kishi started to synthesize bispyridine ligand 2 bearing two hydrophilic methoxyethoxy groups in four steps from 1. He demonstrated that the treatment of the ligands with Pd(II) ions gives rise to M2L4 capsule 3 in a quantitative fashion (Figure 4b). X-ray crystallographic analysis of 3, in collaboration with Dr. Kenji Yoza (Bruker AXS), revealed its capsular nanostructure possessing an isolated cavity with a diameter and volume of ∼1.2 nm and ∼580 Å3, respectively (Figure 4c). In the same period, isostructural M2L4 capsules were prepared by Zhiou Li using various metal ions (e.g., Zn(II), Cu(II), Pt(II), Ni(II), Co(II), and Mn(II) ions).9 She found that the Zn-capsule emits strong blue fluorescence (ΦF = 81%) in CH3CN upon UV light irradiation, whereas the Pdand Pt-capsules are nonemissive. Notably, the Cu-capsule displays solvent-dependent ON/OFF emission properties. Kishi also prepared a photoresponsive Ag(I)-linked M2L2 tube binding fullerenes as a template and a fluorescent Hg(II)-linked M2L4 capsule, convertible into a nonfluorescent M2L2 tube depending on the M/L ratio, in collaboration with the Hayashi group (Kyoto University) and Prof. Hsiu-Fu Hsu (Tamkang University).10,11

Figure 1. Representative, bent building blocks for previous supramolecular capsules and cages.

In 2008 at the Tokyo Institute of Technology (Tokyo Tech), our fresh research group began to develop new supramolecular capsules inspired by fullerene nanostructures that consist of spherical polyaromatic frameworks,5 using our original building block. We first designed anthracene dimer 1 with a meta-phenylene spacer bearing two substituents on the convex side (Figure 2a). Steric repulsion between the orthosubstituents forces the anthracene and phenylene rings into an orthogonal conformation and thus generates a rigid and bent polyaromatic framework (Figure 2b). On the basis of this simple but emergent building block, we further designed two types of polyaromatic capsules using coordination bonds or πstacking interactions/hydrophobic effect. In this Account, we describe the syntheses, structures, and host functions of the supramolecular capsules developed in our group over the course of the past decade.

3.2. Modification of the Bent Ligand

2. WHY THE BENT ANTHRACENE DIMER? Our building block 1 (R = -OCH3) provides the following features: (1) two-step reaction access (>90% yield) from commercially available 1,3-dimethoxybenzene on multigram scale without purification by column chromatography. (2) The dihedral angle (120°) prevents infinite columnar stacking and instead prompts the formation of partially overlapped, discrete stacks. (3) The attachment of hydrophilic substituents on the spacer generates a bent amphiphilic compound with a hydrophilic convex surface and a hydrophobic concave pocket. (4) Various hydrophilic substituents can be attached to the convex side to enhance or tune the water solubility (see Figure 3). (5) The functionalization of the anthracene panels is readily available via halogenation. (6) The connection of the building blocks by other spacers affords multibent polyaromatic frameworks. (7) The replacement of the anthracene panels with other panels can alter the character of the bent framework. Finally, (8) the phenylene spacer is also replaceable with other spacers to modify the distance or angle of the two panels. With multifeatured compound 1 in hand, we set out to develop new supramolecular capsules with valuable functions.6

An analogue of Pd-capsule 3 with naphthylene spacers was synthesized by Tsubasa Yuki in 2015, possessing an anisotropically expanded cavity (Figure 5a,b).12 Kohei Yazaki and Shogo Noda obtained M2L4 capsules bearing cationic acridinium and redox-active dihydrophenazine panels, respectively, using the corresponding bent ligands in 2016 (Figure 5c,d).13 More recently, Takahiro Tsutsui prepared a Pt(II)-linked M2L4 cage possessing a cavity covered by desymmetrized bispyridine ligands with a single anthracene panel (Figure 5e,f).14 The open cavity enables binding of larger pigments, which cannot be encapsulated by the closed cavity of 3. 3.3. Anticancer Activity

Dr. Anife Ahmedova (Univesity of Sofia) clarified in 2016 that the anticancer activities of Pt(II)/Pd(II)-linked capsules 3 toward leukemic cells (HL-60 and SKW-3) are superior to that of cisplatin.15 Additionally, pronounced toxicities of the capsules toward cisplatin-resistant cells were observed. Importantly, the cytotoxic selectivities of the capsules against noncancerous/cancerous kidney cells (HEK-293) were up to 5-fold higher than that of cisplatin.

Figure 2. (a) Bent anthracene dimer 1 and (b) its DFT optimized structure. B

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Figure 3. Overview of the modular variations of building block 1.

Figure 5. (a) Naphthylene-based ligand and (b) the corresponding M2L4 cage (R = -H for clarity). (c) Acridinium- and (d) dihydrophenazine-based ligands. (e) Desymmetrized ligand and (f) the corresponding M2L4 cage. Unless otherwise indicated, the optimized structures throughout the text were obtained by forcefield calculation (with the FORCITE module of Materials Studio (Accelrys Software Inc.)).

Figure 4. (a) Concept of our first coordination capsule: an M2L4 capsule with a polyaromatic shell. (b) Formation of 3 and (c) its crystal structure (R = -H for clarity).

host and guest. In 2015, Masahiro Yamashina successfully prepared highly fluorescent host−guest complexes in water using Pt-capsule 3 with 12 methoxyethoxy groups, which enhance its water solubility.17 The emissivity of fluorescent dyes is usually quenched by the proximity to transition metal ions so that coordination cages and capsules displaying strong guest emission are uncommon.3b Capsule 3 itself is nonemissive despite bearing anthracene fluorophores. However, upon encapsulation of pentamethyl BODIPY, coumarin 153 (C153), or Nile red, Yamashina found that the resultant host− guest complexes show strong fluorescence (Figure 6c), in collaboration with the Tahara group (RIKEN). Notably, the emission color of the BODIPY guest could be modulated upon coencapsulation.17

3.4. Host Capabilities Toward Synthetic Molecules

Owing to the ∼1 nm sized, hydrophobic cavity surrounded by multiple anthracene panels, Pd-capsule 3 displayed wideranging host capabilities toward synthetic molecules (Figure 6a) in aqueous solutions, which was first demonstrated by Kishi in collaboration with Prof. Jay S. Siegel (Tianjin University).7,16 The capsule quantitatively encapsulated, e.g., one molecule of [2.2]paracyclophane or two molecules of corannulene in the cavity, through the hydrophobic effect and π−π/CH−π interactions. From a C60/C70 mixture or fullerene soot, exclusive encapsulation of C60 by 3 was accomplished (Figure 6b), due to the complementary size and shape of the C

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AMMVN is enhanced by >640 times as compared with that of free AMMVN (Figure 7b).18 The observed, unusual stability stems from the tighter encapsulation and effective compression of C-shaped AMMVN by the rigid frameworks of 3 (Figure 7d). Stabilized reagents 3·AIBN and 3·AMMVN could be utilized for typical radical polymerizations after spontaneous release of the initiators in organic solvent. Oligosulfurs are uncommon inorganic guest molecules,19 and the mass spectrometry (MS) analysis displays only their fragment peaks, because of their instability under MS conditions. In 2017, Sho Matsuno revealed that capsule 3 quantitatively encapsulates two molecules of cyclooctasulfur (S8) upon stirring in water (Figure 8a).20 The standard

Figure 6. (a) Synthetic guests for 3 and (b) selective fullerene encapsulation by 3. (c) Fluorescent host−guest complexes.

3.5. Modulation of Guest Reactivities

Our next investigation focused on the stabilization of reactive reagents. We envisioned that the polyaromatic shell of 3 could protect bound radical initiators from UV light, due to the light shielding effect. In 2014, Yamashina demonstrated the remarkable stability of 2,2′-azobis(isobutyronitrile) (AIBN) against light within 3.18 Upon quantitative encapsulation by 3, the fully insulated AIBN was significantly stabilized toward UV light and the half-life (τ1/2) was >380 times longer than that of free AIBN (Figure 7a,c). A larger AIBN derivative, AMMVN, is a highly reactive initiator triggered by heating. He encountered that upon encapsulation, the thermal stability of

Figure 8. (a) Encapsulation of S8 by 3 and its ESI-TOF MS spectrum. (b) In situ synthesis of S12 from (S6)2 within 3. Structures of (c) 3· (S8)2 and (d) 3·S12 (R = -H for clarity).

electrospray ionization-time-of-flight mass spectrometry (ESITOF MS) analysis of product 3·(S8)2 displayed its intrinsic MS peaks, without the cluster decomposition. Thanks to the protection of the bound guests (Figure 8c) and the promotion of efficient ionization, tetracationic 3 acted as an ionic capsular matrix for the detection of the exact molecular weight of S8. Remarkable stabilization of otherwise labile S6 by 3 was observed not only under MS conditions but also in an ambient solution state (Figure 8b). ESI-TOF MS analysis of 3·(S6)2 showed the target MS peaks. Oligosulfurs are photosensitive and decompose into complex polymers upon light irradiation. Nevertheless, Matsuno challenged and eventually succeeded in in situ selective synthesis of cyclic S12 from (S6)2 within 3 (Figure 8b), upon light irradiation (425 nm) in the glassy state. The product structure was confirmed by NMR, MS, molecular modeling studies (Figure 8d), and Raman analysis, in collaboration with the Yamamoto group (Tokyo Tech). He opened up a new function of capsule 3 as a molecular flask4 for inorganic synthesis. 3.6. Selective Recognition of Biomolecules

The water-solubility and the relatively large cavity of capsule 3 prompted us to examine its recognition ability toward biomolecules. Xanthines exhibit different bioactivities depend-

Figure 7. Stabilization of radical initiators (a) AIBN and (b) AMMVN by 3. Crystal structures of (c) 3·AIBN and (d) 3·AMMVN (R = -H for clarity). D

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monosaccharides resulted in no host−guest complex formation. Combined with the 2D NMR analysis, theoretical calculation studies in collaboration with the Hayashi group indicated that the observed, strict SU recognition stems from (i) an effective steric match and (ii) multiple CH−π interactions between the hydrocarbon-based guest backbone and the polyaromatic host cavity (Figure 10b). The recognition method of 3 is in marked contrast to that of natural saccharide receptors that rely on multiple hydrogenbonding interactions. Yamashina further explored the binding ability of 3 toward artificial sugar substitutes. Chlorinated SU (i.e., sucralose) and amino acid-based aspartame were captured by 3, in accordance with bioreceptors, stronger than natural sugars, due to increased hydrophobicity and additional π−π interactions, respectively (Figure 10c).22 We next picked oligo(lactic acid)s, which are relevant to biodegradable materials, to study their host−guest interactions in water. In 2018, Shunsuke Kusaba demonstrated that tetra(lactic acid) (4LA) is preferentially bound by 3 from a complex mixture of oligo(lactic acid)s (Figure 11a).23 The

ing only on the number of methyl groups. In 2016, Matsuno found out that capsule 3 exclusively binds caffeine (CF) molecules from a mixture of three xanthines, i.e., CF, theobromine (TB), and theophylline, in water (Figure 9a).21

Figure 9. (a) Selective caffeine recognition by 3. CH3−π interactions within (b) 3·(CF)2 and (c) 3·(TB)2 (R = -H for clarity).

Selective CF binding was possible even from instant coffee. Xray crystal analysis of the host−guest complexes evidenced that multiple CH3−π interactions are essential for the recognition (Figure 9b,c). Beyond our expectations, Yamashina discovered in 2017 that D-sucrose (SU), a highly hydrated biomolecule with several isomers, can be selectively encapsulated by capsule 3 even in water.22 Simple mixing of 3 with highly hydrophilic SU in water led to the formation of host−guest complex 3·SU in >85% yield (Figure 10a). On the other hand, mixing with other disaccharides (e.g., D-trehalose and D-maltose) as well as

Figure 11. (a) Preferential oligo(lactic acid) binding by 3 and (b) the structure and host−guest interactions of 3·4LA (R = -H for clarity).

binding constant for water-soluble 4LA by the hydrophobic cavity was relatively high even in water. The X-ray crystallographic analysis of 3·4LA clarified the importance of multiple, host−guest CH−π/hydrogen-bonding interactions for the binding (Figure 11b). In addition, the formation of the host−guest complex was an enthalpically favorable process (ΔH = −40 kJ mol−1 and TΔS = −8.3 kJ mol−1 at 25 °C), as indicated by ITC analysis. The remarkable stabilization of lactide against hydrolysis was also observed within 3. Very recently, unique recognition of male sex hormones was achieved by Yamashina. A human androgen receptor selectively binds “male” androgenic hormones over “female” progestogenic and estrogenic hormones. However, synthetic receptors with such an ability have not been developed so far. He demonstrated that capsule 3 encapsulates male testosterone (TES) in >98% selectivity from a 1:1:1 as well as 1:100:100 mixture of TES and female progesterone (PRG) and β-estradiol (ESD) in water (Figure 12a).24 Competitive binding studies further elucidated the high affinity of 3 toward various male hormones: TES ≈ dihydrotestosterone (♂) > androstenedione (♂) > androsterone (♂) ≫ PRG > 17αhydroxyprogesterone (♀) > ESD > estriol (♀) (Figure 12c). The observed, remarkable selectivity arises from multiple host−guest CH/OH−π/hydrogen-bonding interactions in the cavity, established by the crystal structure analysis of 3·TES (Figure 12b). More importantly, the spherical cavity of 3 was converted to an elliptical one through encapsulation of TES. This guest-induced conformational change plays a key role in the present shape discrimination of the large and rigid

Figure 10. (a) Selective sucrose recognition by 3 in water and (b) the structure of 3·SU. (c) Binding order of artificial and natural sugars by 3. E

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Figure 13. (a) Cramming of 5EO and threading of 10EO into 3 in water. Structures of (b) 3·5EO and (c) 3·10EO (R = -H for clarity). (d) Formation of pseudorotaxane-shaped complex (3)2·22EO.

Figure 12. (a) Selective testosterone binding by 3. (b) Structure and host−guest interactions of 3·TES (R = -H for clarity). (c) Binding order of male/female hormones by 3.

3.8. Double and Peanut-Shaped Capsules

Unlike intensive studies on molecular cages and capsules with a single cavity, capsular structures providing multiple cavities have been seldom explored.26 Conceptually combining capsule 37 and a wire-framed double cage27 developed by the Chand group (Indian Institute of Technology, Madras), we designed a polyaromatic M3L4 double capsule with two isolated cavities. In 2017, Kohei Yazaki synthesized tripyridine ligand 4a containing two building blocks 1 and succeeded in the quantitative formation of M3L4 double capsule 5a upon treatment with Pd(II) ions (Figure 14a), in collaboration with the Chand group.28 The crystal structure, obtained with support by Dr. Hiroyasu Sato (Rigaku Corporation), elucidated its ∼3 nm-long dumbbell-shaped framework consisting of two polyaromatic spheres linked together (Figure 14b). Each of the cavities (∼500 Å3 in volume) is fully encircled by eight anthracene panels. Double capsule 5a quantitatively bound two molecules of C60 in the two cavities, yet under concomitant dissociation of the central Pd(II) ion. Yazaki obtained the peanut-shaped M2L4 capsule 5a′ including two C60 molecules, when a DMSO solution of 5a and C60 was heated at 110 °C (Figure 14c).28 Similar host−guest complexes were formed quantitatively using C70 and metallofullerene Sc3N@C80. The selective heteroleptic encapsulation of one elliptical diamantane and two planar phenanthrenes was accomplished using 5a, due to the cooperative volume changes of the linked cavities upon guest encapsulation (Figure 14c).28,29 Very recently, we updated the peanut-shaped capsule by employing bipyridine ligand 4b with a phenylene spacer. Due to the reduction of the metal-binding sites, Kyosuke Matsumoto selectively obtained peanut-shaped M2L4 capsule 5b in CH3CN/H2O and an ML2 double tube in DMSO

biomolecules. Yamashina furthermore set up a fluorescent detection system for a nanogram amount of TES.24 The emission of host−guest complex 3·C153 decreased, when the guest was displaced by more hydrophobic TES in the cavity. 3.7. Cramming and Threading of Linear Amphiphiles

Oligo- and poly(ethylene oxide)s, showing weak interactions with aliphatic/aromatic frameworks, are widely usable amphiphiles in materials chemistry and biochemistry. In 2018, Yamashina came across unusual host−guest structures composed of 3 and such oligomers in water.25 He found that one molecule of short penta(ethylene oxide) (5EO) is quantitatively bound by 3 with a roughly coiled conformation (Figure 13a,b), which was clearly characterized by X-ray crystallographic analysis supported by Dr. Takashi Kikuchi (Rigaku Corporation). Similarly, the tetramer to the octamer were crammed into the closed cavity of 3 in water. Unexpectedly, Yamashina also found that capsule 3 even binds decamer 10EO, with an extended length of ∼4 nm, to form pseudorotaxane-shaped 3·10EO quantitatively in water (Figure 13a,c).25 The relatively strong host−guest interactions (Ka = 1.1 × 106 M−1) were elucidated by ITC analysis conducted by Kusaba. Moreover, poly(ethylene oxide)s with ∼7 nm in extended length (e.g., 22EO) were bound by the capsules to predominantly give unique 2:1 host−guest complex (3)2·22EO in water (Figure 13d). By ITC analysis, the enthalpy and entropy changes for the 2:1 complex formation were estimated to be both large negative values (ΔH = −131 kJ mol−1 and TΔS = −99.6 kJ mol−1 at 25 °C).25 The large entropy loss is mainly caused by the restricted motion of the long chains of the poly(ethylene oxide)s upon their threading into the capsules. F

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Figure 15. (a) Interconvertible peanut-shaped capsule 5b and its fullerene encapsulation. (b) Crystal structure of 5b·(C60)2 (sliced representation, R = -H for clarity).

Figure 14. (a) Formation of double capsule 5a and (b) its crystal structure (R = -H for clarity). (c) Formation of peanut-shaped host− guest complex 5a′·(C60)2 and a heteroleptic complex.

(Figure 15a), as interconvertible structures.30 Capsule 5b encapsulated two molecules of C60 under mild conditions, in contrast to 5a. The crystal structure of 5b·(C60)2 eventually provided clear evidence for the close proximity yet noncontact of the fullerene dimer, with a van der Waals separation of 3 Å (Figure 15b). Matsumoto also investigated the electronic properties of 5b·(C60)2, which generates unusual (C60•−)2, C60•−·C602−, and (C602−)2 species upon sequential reduction, in collaboration with the Haga group (Chuo University).30

Figure 16. (a) Concept of our first π-stacking capsule: a micellar capsule composed of bent polyaromatic amphiphiles. (b) Formation of capsule 7 and its optimized structure.

Thanks to its bent polyaromatic surfaces and highly watersoluble substituents, the amphiphiles spontaneously and quantitatively assembled into spherical capsule 7, with an average formula of (6)5 and an average core diameter of ∼1 nm, in water (Figure 16b). The product size and shape in both the solution and dry state were analyzed by AFM, which is usually impossible in the case of conventional micelles, with the support of Shiho Moriguchi and Akinori Kogure (Shimadzu Analytical & Measuring Center, Inc.). The capsular assembly is sufficiently stable in water under elevated temperatures (up to ∼70 °C) and in a wide pH range (pH 1−13), due to the hydrophobic effect and π-stacking interactions between the anthracene panels. The cationic hydrophilic groups of 6 are replaceable by anionic sulfonate (6′) or zwitterionic sulfobetaine groups so that the electrostatic properties on the outer surfaces of 7 are readily adjustable.32,33

4. π-STACKING CAPSULES 4.1. Synthesis and Structure

On the basis of typical micelles bearing hydrophobic aliphatic chains, we designed a micellar capsule composed of hydrophobic, bent polyaromatic frameworks (Figure 16a). In 2013, 100 years since the first introduction of the word “micelle” by McBain,31 we reported π-stacking capsules as a new class of micellar assemblies, termed “aromatic micelle”, providing wideranging host capabilities in water.32 Kei Kondo initially synthesized amphiphile 6 with two trimethylammonium groups in four steps from building block 1 (R = -OCH3). G

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conversion into cis/trans-amphiphilic molecules (R = -OCH2CH2CH2SO3Na) was accomplished by Akira Suzuki in 2013 (Figure 18a).37 Whereas the S-shaped transamphiphile yielded oligomeric aggregates in water, the Cshaped cis-amphiphile quantitatively generated a spherical dimeric capsule under the same conditions. The capsule showed host−guest charge-transfer interactions upon encapsulation of quinones.37 In 2016, Suzuki further elongated the bent amphiphilic structure and synthesized a U-shaped anthracene tetramer in >80% selectivity (Figure 18b) from a mixture of the three isomers.38 A dimeric capsule spontaneously formed from the U-shaped amphiphiles acted as a fluorescent probe to decode the structural information on monoterpenes. Very recently, Tomoya Nishioka connected two molecules of 6′ by an acetylene unit to create a new gemini-type amphiphile (Figure 18c).39 The gemini amphiphiles assembled into a well-defined capsule (∼2 nm in core diameter), providing high stability in water at high temperature (>130 °C), due to highly effective π-stacking interactions.

Starting from 6, Kondo prepared its derivatives bearing various substituents, such as -Br, -CN, and -CCPh, on the anthracene panels (Figure 17a).34 The corresponding π-stacking capsules

4.4. Water Solubilization of Organic Dyes and Nanocarbons

Figure 17. Modulation of bent amphiphiles through (a) functionalization and (b) replacement of the anthracene panels.

Kondo revealed that, taking advantage of the adaptable polyaromatic shell, π-stacking capsule 7 incorporates a very wide range of hydrophobic aromatic molecules into the cavity in water. Fluorescent dyes such as Nile red (NR) and dicyanomethylenepyran derivative DCM were encapsulated in 7 by means of simply stirring a mixture of 6 and the corresponding dye in water (Figure 19a,b).32 The resultant solutions of the host−guest complexes with NR and DCM guests were blue and red, respectively. Notably, moderate red fluorescence (ΦF = 23%) from the guest was observed upon irradiation of 7·(DCM)n at the host absorption band (370 nm), due to efficient host-to-guest energy transfer (>95% efficiency). The local environment within 7 was also investigated by steady-state and time-resolved spectroscopy, in collaboration with the Tahara group.40 In 2015, Kondo established a grinding protocol for the facile water-solubilization of various nanocarbons using 6 through encapsulation (Figure 19a, right).41 The typical procedure is to grind a mixed solid of 6 and C60 (in a 2:1 ratio) for ∼1 min using a mortar and pestle. Following sequential water addition, centrifugation, and filtration for the removal of excess C60 gave rise to a clear brown solution of 7·C60. The quantitative

were formed in water in a manner similar to 7. On the other hand, the fluorescent properties of the resultant capsules were largely changed depending on the substituents. In 2015, Yusuke Okazawa elucidated the usability of other (poly)aromatic panels apart from the anthracene panels as frameworks for the capsule. He synthesized bent amphiphiles with phenanthrene, naphthalene,33 pentamethylbenzene (8), and benzene rings (Figure 17b).35 Interestingly, the fluorescent intensities of the phenanthrene- and naphthalene-based amphiphiles were enhanced by 1.3 and >2 times, respectively, through capsule formation in water. These observations represent an aggregation-induced enhanced emission (AIEE) effect. The new AIEE-active capsules also displayed emission enhancement upon guest encapsulation.33 Pentamethylbenzene-based amphiphiles 8 enhanced the water-solubility of fluorescein and Eosin Y upon encapsulation.35 4.3. Elongation of the Bent Amphiphile

An anthracene trimer with two meta-phenylene spacers (R = -OH) was initially synthesized by Junji Iwasa36 and its

Figure 18. Elongated bent amphiphiles and their structures: (a) a C-shaped trimer, (b) a U-shaped tetramer, and (c) a gemini-type tetramer. H

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6.41 The obtained clear black solution of 7·SWCNT is stable enough in water for >1 month (Figure 19g). In the same way, multiwalled CNTs with wider diameters (∼10 nm) were readily solubilized upon encapsulation by 7. 4.5. Water Solubilization of Metal-Complexes

Whereas unfunctionalized Cu(II)-phthalocyanine (CuPc) and their larger derivatives (Figure 20a) show no solubility in

Figure 19. (a) Schematic representation of the guest encapsulation by 7. (b) Fluorescent, (c) fullerene, and (d) nanographene guests for 7. (e) Optimized structure of 7·C60. (f) STM image of released DCO on Au(111). (g) Water solubilization of SWCNT using 6.

Figure 20. (a) Metal-phthalocyanine guests for 7 and (b) structure of 7·(CuPc)2. (c) Metal-porphyrin guests for 7. (d) Catalytic epoxidation of chlorostyrene by 7·MnPrF in water.

formation of the host−guest complex (based on 6) and the detailed structure were confirmed by the combination of UVvisible, DLS, AFM, and molecular modeling analyses (Figure 19e). The same grinding protocol afforded water-soluble host−guest complexes incorporating not only higher fullerenes (e.g., C70, C84, and C120; Figure 19c) but also various nanographenes, such as pentacene, coronene, hexabenzocoronene, ovalene, and dicoronylene (DCO; Figure 19d), in collaboration with the Matsuo group (The University of Tokyo) and the Yoshimoto group (Kumamoto University). The planar guests were efficiently accommodated in stacked fashions. In 2018, Sakura Origuchi revealed that the encapsulated DCO guests can be gradually released from 7 under acidic conditions, resulting in the formation of a highly ordered adlayer on a Au(111) surface (Figure 19f).42 Owing to the strong bundling peculiarity, water-solubilization of single-walled carbon nanotubes (SWCNT) was performed by a combination of grinding and sonication with

water, simply grinding the metal-complexes with 6 led to the formation of water-soluble host−guest complexes (Figure 20b), as investigated by Kondo in 2016. 43 He also demonstrated that the bound CuPc guests can be released from 7 into bulk solvent, when the host structure is disassembled upon addition of polar organic solvent. The guests were furthermore released onto glass or polymer plates by casting of the host−guest solution followed by washing with methanol to remove only 6. In the same period, Takumi Omagari showed that metaltetraphenylporphyrins (MPr) are bound by 7 to form watersoluble 1:1 host−guest complexes 7·MPr (Figure 20c).44 Among them, he employed 7·MnPr as a capsular catalyst for the epoxidation of styrenes in water. Catalytic conversion of 2chlorostyrene yielded the corresponding epoxide in high yield and efficiency (81% yield and turnover number of 1350) within 1 h at room temperature using a capsular catalyst I

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Accounts of Chemical Research bearing perfluorinated derivative MnPrF without imidazole ligands (Figure 20d). In contrast, the reaction barely proceeded using unencapsulated MnPrF in organic solvent (THF) under similar conditions (2% yield). The observed, high catalytic performance stems from (i) the enforced proximity of the catalytic center and the substrates and (ii) the smooth replacement of the slightly hydrophilic products by the more hydrophobic substrates within 7. 4.6. Encapsulation-Induced Emission Enhancement

Unlike organic fluorescent dyes, Eu(III)-complexes with multiple chelating ligands emit intense red luminescence in aprotic solvents, yet the emission is completely quenched in the presence of aqueous solvents. Tomokuni Kai revealed that the high emissivity of Eu-1 in an anhydrous CH3CN solvent (ΦF = 54%) can be maintained to a high degree even in water (ΦF = 48%) upon encapsulation by capsule 9 composed of pentamethylbenzene-based amphiphiles 8 (Figures 17b and 21a).45 Surprisingly, the weak red emission from free Eu-2 in Figure 22. (a) pH-responsive amphiphile 10 and (b) guest release from 11 in water upon addition of acid. (c) Dye guests for 11.

subsequently released them by simple addition of HCl (Figure 22b,c). Dr. Lorenzo Catti and Natsuki Kishida succeeded very recently in the incorporation of photo switches into the capsular frameworks and accomplished the photoresponsive guest release from the new π-stacking capsules.47 As the photo switch, they employed an ortho-dianthrylbenzene unit and synthesized the corresponding bent amphiphiles 12o (Figure 23a). The amphiphiles quantitatively assembled into spherical capsule 13, with a core diameter of ∼2 nm, in water through πstacking interactions and the hydrophobic effect. Unlike metasubstituted 6, the capsular structure quickly and quantitatively disassembled into the monomeric species by light irradiation, through structural conversion from open 12o to closed 12c. Notably, regeneration of 13 took place by photoirradiation or heating of 12c. With the aid of the wide-ranging host capability, the photoinduced, quantitative release of various guests, such as NR, C60, CuPc, and ZnPr was demonstrated by using 13 in water (Figure 23b,c,e). The uptake and release functions were furthermore applied to the fluorescence modulation of slightly water-soluble C314. About 10-fold emission enhancement was observed upon UV light irradiation of 13·(C314)2 through guest release (Figure 23d).

Figure 21. (a) Encapsulation of Eu(III)-complexes by 9 composed of amphiphiles 8 and the emission data (λex = 375 nm) in water and (b) structure of 9·Eu-2.

CH3CN was enhanced by >6 times within 9 in water (ΦF = 27%), accompanied by the elongation of its emission lifetime (∼3-fold). The observed photophysical properties are most probably caused by the steric protection of the Eu-complexes against water molecules and the restricted rotation of its aromatic rings upon tight encapsulation by 9 (Figure 21b). Accordingly, encapsulation-induced emission enhancement (EIEE) of the Eu(III)-complexes was demonstrated using the π-stacking capsule in water.

5. SUMMARY AND OUTLOOK We have presented our investigations into a bent anthracene dimer and its derivatives as versatile building blocks for supramolecular capsules over the past decade. Since the first design and synthesis of our coordination and π-stacking capsules (Figures 4 and 16), we have explored their characteristic functions derived mainly from their cavities surrounded by the polyaromatic panels in water. The studies revealed that the host functions of these two kinds of capsules are complementary to each other. Namely, the coordination capsules act as rigid molecular receptors with high selectivity and preference, yet the π-stacking capsules act as flexible molecular containers with high adaptability to the size and shape of guest molecules. As future perspectives, through their further investigation,48 we aim to make the present capsules valuable “molecular tools” for synthetic, analytical, material, biological, and/or medical researchers. In addition, we

4.7. Stimuli-Responsive Capsules

To expand the usability of the π-stacking capsules, we examined the incorporation of stimuli-responsive switches into 6 to create new supramolecular capsules with both guest uptake and release functions in water. In 2017, Mai Kishimoto developed a pH-responsive capsule comprising amphiphiles 10 with two acridine panels, which convert to cationic and hydrophilic panels upon protonation by the addition of acid (Figure 22a).46 She revealed that the assembly and disassembly of capsule 11 occur reversibly in water under neutral and acidic conditions, respectively (≥10 cycles). In addition, 11 encapsulated a variety of hydrophobic dyes such as coumarin 314 (C314) and subphthalocyanine in neutral water and J

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Accounts of Chemical Research Biographies

Michito Yoshizawa received his Ph.D. degree from Nagoya University in 2002. He was a JSPS postdoctoral fellow in 2002− 2003 and Assistant Professor in the Fujita group at The University of Tokyo in 2003−2008. He has been appointed Associate Professor at Chemical Resources Laboratory (2008−2016) and Laboratory for Chemistry and Life Science, Institute of Innovative Research (2016− present), Tokyo Institute of Technology. He was a Visiting Professor at University of Strasbourg in 2006 and 2014. His research interests focus on the development of functional polyaromatic nanospaces. Lorenzo Catti received his Master’s degree in organic chemistry from the Technical University of Munich in 2013 under the supervision of Prof. Konrad Tiefenbacher. In 2016, he moved with the Tiefenbacher group to the University of Basel and, in 2017, completed his Ph.D. research on the application and development of resorcinarene-based supramolecular catalysts. He is currently a JSPS/AvH postdoctoral fellow in the Yoshizawa group at the Tokyo Institute of Technology.

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ACKNOWLEDGMENTS M.Y. thanks all of his group members with whom he worked together at Tokyo Tech. In addition, notable research support from Prof. Munetaka Akita, Dr. Yuya Tanaka, Hitomi Otomo, Prof. Kimihisa Yamamoto and his staff (Laboratory for Chemistry and Life Science, Tokyo Tech), Dr. Yoshihisa Sei, and Dr. Motoya Suzuki (Technical Department, Tokyo Tech), and Dr. Jeremy K. Klosterman (University of California San Diego) are greatly acknowledged.

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Figure 23. (a) Light-induced conversion of amphiphile 12o to 12c and (b) guest release from 13 in water upon light irradiation. (c) UV−visible spectra (H2O, r.t.) before/after guest release. (d) Fluorescence spectra (H2O, r.t., λex. = 445 nm) before/after guest release. (e) The structure of 13·(NR)2.

anticipate that the utilization of other bond types, e.g., hydrogen,2a ionic,49 or dynamic covalent bonds,50 for the assembly of the present building blocks will lead to the generation of new and exciting supramolecular capsules, which we hope to explore in our future studies.

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REFERENCES

(1) (a) Lehn, J.-M. Supramolecular Chemistry: Concepts and Perspectives; VCH: Weinheim, Germany, 1995. (b) Steed, J. W.; Atwood, J. L. Supramolecular Chemistry, 2nd ed.; Wiley: Chichester, U.K., 2009. (2) (a) Hof, F.; Craig, S. L.; Nuckolls, C.; Rebek, J., Jr. Molecular encapsulation. Angew. Chem., Int. Ed. 2002, 41, 1488−508. (b) Chakrabarty, R.; Mukherjee, P. S.; Stang, P. J. Supramolecular coordination: self-assembly of finite two- and three-dimensional ensembles. Chem. Rev. 2011, 111, 6810−6918. (c) Cook, T. R.; Zheng, Y. R.; Stang, P. J. Metal-organic frameworks and selfassembled supramolecular coordination complexes: comparing and contrasting the design, synthesis, and functionality of metal-organic materials. Chem. Rev. 2013, 113, 734−777. (d) Harris, K.; Fujita, D.; Fujita, M. Giant hollow MnL2n spherical complexes: structure, functionalisation and applications. Chem. Commun. 2013, 49, 6703− 6712. (e) Yoshizawa, M.; Klosterman, J. K. Molecular architectures of multi-anthracene assemblies. Chem. Soc. Rev. 2014, 43, 1885−1898. (f) Chen, L.-J.; Yang, H.-B.; Shionoya, M. Chiral metallosupramolecular architectures. Chem. Soc. Rev. 2017, 46, 2555−2576. (g) Rizzuto, F. J.; von Krbek, L. K. S.; Nitschke, J. R. Strategies for binding multiple guests in metal-organic cages. Nat. Rev. Chem. 2019, 3, 204−222. (3) (a) Dsouza, R. N.; Pischel, U.; Nau, W. M. Fluorescent dyes and their supramolecular host/guest complexes with macrocycles in aqueous solution. Chem. Rev. 2011, 111, 7941−7980. (b) Xu, L.; Wang, Y.-X.; Yang, H.-B. Recent advances in the construction of fluorescent metallocycles and metallocages via coordination-driven self-assembly. Dalton Trans. 2015, 44, 867−890. (c) Diaz-Moscoso, A.; Ballester, P. Light-responsive molecular containers. Chem. Commun. 2017, 53, 4635−4652. (4) (a) Yoshizawa, M.; Klosterman, J. K.; Fujita, M. Functional molecular flasks: new properties and reactions within discrete, selfassembled hosts. Angew. Chem., Int. Ed. 2009, 48, 3418−3438. (b) Brown, C. J.; Toste, F. D.; Bergman, R. G.; Raymond, K. N. Supramolecular catalysis in metal-ligand cluster hosts. Chem. Rev. 2015, 115, 3012−3035. (c) Galan, A.; Ballester, P. Stabilization of

AUTHOR INFORMATION

Corresponding Author

*Fax: (+81)45-924-5230. E-mail: [email protected]. jp. ORCID

Michito Yoshizawa: 0000-0002-0543-3943 Lorenzo Catti: 0000-0003-0727-0620 Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Funding

Our recent research projects were supported by JSPS KAKENHI (Grant No. JP17H05359, JP18H01990, JP19H04566) and “Support for Tokyotech Advanced Researchers (STAR)”. L.C. thanks the JSPS and Humboldt Postdoctoral Fellowship. Notes

The authors declare no competing financial interest. K

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Accounts of Chemical Research reactive species by supramolecular encapsulation. Chem. Soc. Rev. 2016, 45, 1720−1737. (d) Zhang, Q.; Catti, L.; Tiefenbacher, K. Catalysis inside the hexameric resorcinarene capsule. Acc. Chem. Res. 2018, 51, 2107−2114. (e) Sinha, I.; Mukherjee, P. S. Chemical transformations in confined space of coordination architectures. Inorg. Chem. 2018, 57, 4205−4221. (5) (a) Kroto, H. W.; Heath, J. R.; O’Brien, S. C.; Curl, R. F.; Smalley, R. E. Nature 1985, 318, 162−163. (b) Hirsch, A.; Brettreich, M. Fullerenes: Chemistry and Reactions; Wiley-VCH: Weinheim, Germany, 2005. (6) Studies on other structures using this or similar building blocks: (a) Yazaki, K.; Kishi, N.; Akita, M.; Yoshizawa, M. A bowl-shaped organic host using bispyridine ligands: selective encapsulation of carbonyl guests in Water. Chem. Commun. 2013, 49, 1630−1632. (b) Yazaki, K.; Sei, Y.; Akita, M.; Yoshizawa, M. A polyaromatic molecular tube that binds long hydrocarbons with high selectivity. Nat. Commun. 2014, 5, 5179. (c) Sekiguchi, S.; Kondo, K.; Sei, Y.; Akita, M.; Yoshizawa, M. Engineering stacks of V-shaped polyaromatic compounds with alkyl chains for enhanced emission in the solid state. Angew. Chem., Int. Ed. 2016, 55, 6906−6910. (d) Jono, K.; Suzuki, A.; Akita, M.; Albrecht, K.; Yamamoto, K.; Yoshizawa, M. A polyaromatic molecular clip that enables the binding of planar, tubular, and dendritic compounds. Angew. Chem., Int. Ed. 2017, 56, 3570−3574. (e) Yazaki, K.; Catti, L.; Yoshizawa, M. Polyaromatic molecular tubes: from strategic synthesis to host functions. Chem. Commun. 2018, 54, 3195−3206. (f) Kuroda, K.; Yazaki, K.; Tanaka, Y.; Akita, M.; Sakai, H.; Hasobe, T.; Tkachenko, N. V.; Yoshizawa, M. A pentacene-based nanotube displaying enriched electrochemical and photochemical activity. Angew. Chem., Int. Ed. 2019, 58, 1115−1119. (7) (a) Kishi, N.; Li, Z.; Yoza, K.; Akita, M.; Yoshizawa, M. An M2L4 molecular capsule with an anthracene shell: encapsulation of large guests up to 1 nm. J. Am. Chem. Soc. 2011, 133, 11438−11441. (b) Yoshizawa, M.; Yamashina, M. Coordination-driven nanostructures with polyaromatic shells. Chem. Lett. 2017, 46, 163−171. (8) (a) Debata, N. B.; Tripathy, D.; Chand, D. K. Self-assembled coordination complexes from various palladium(II) components and bidentate or polydentate ligands. Coord. Chem. Rev. 2012, 256, 1831− 1945. (b) Han, M.; Engelhard, D. M.; Clever, G. H. Self-assembled coordination cages based on banana-shaped ligands. Chem. Soc. Rev. 2014, 43, 1848−1860. (9) (a) Li, Z.; Kishi, N.; Hasegawa, K.; Akita, M.; Yoshizawa, M. Highly fluorescent M2L4 molecular capsules with anthracene shells. Chem. Commun. 2011, 47, 8605−8607. (b) Li, Z.; Kishi, N.; Yoza, K.; Akita, M.; Yoshizawa, M. Isostructural M2L4 molecular capsules with anthracene shells: synthesis, crystal structures, and fluorescent properties. Chem. - Eur. J. 2012, 18, 8358−8365. (10) (a) Kishi, N.; Akita, M.; Kamiya, M.; Hayashi, S.; Hsu, H.-F.; Yoshizawa, M. Facile catch and release of fullerenes using a photoresponsive molecular tube. J. Am. Chem. Soc. 2013, 135, 12976−12979. (b) Kishi, N.; Akita, M.; Yoshizawa, M. Selective hostguest interactions of a transformable coordination capsule/tube with fullerenes. Angew. Chem., Int. Ed. 2014, 53, 3604−3607. (11) (a) Kishi also studied in the Nitschke group (University of Cambridge) for several months during his Ph.D. course. (b) Foster, J. A.; Parker, R. M.; Belenguer, A. M.; Kishi, N.; Sutton, S.; Abell, C.; Nitschke, J. R. Differentially addressable cavities within metal-organic cage-cross-linked polymeric hydrogels. J. Am. Chem. Soc. 2015, 137, 9722−9729. (12) Yamashina, M.; Yuki, T.; Sei, Y.; Akita, M.; Yoshizawa, M. Anisotropic expansion of an M2L4 coordination capsule: host capability and frame rearrangement. Chem. - Eur. J. 2015, 21, 4200−4204. (13) (a) Yazaki, K.; Sei, Y.; Akita, M.; Yoshizawa, M. Polycationicshelled capsular and tubular nanostructures and their anionic-guest binding properties. Chem. - Eur. J. 2016, 22, 17557−17561. (b) Yazaki, K.; Noda, S.; Tanaka, Y.; Sei, Y.; Akita, M.; Yoshizawa, M. An M2L4 molecular capsule with a redox switchable polyradical shell. Angew. Chem., Int. Ed. 2016, 55, 15031−15034.

(14) Tsutsui, T.; Kusaba, S.; Yamashina, M.; Akita, M.; Yoshizawa, M. Open versus closed polyaromatic nanocavity: enhanced host abilities for large dyes and pigments. Chem. - Eur. J. 2019, 25, 4320− 4324. (15) (a) Ahmedova, A.; Momekova, D.; Yamashina, M.; Shestakova, P.; Momekov, G.; Akita, M.; Yoshizawa, M. Anticancer potencies of Pt(II)- and Pd(II)-linked M2L4 coordination capsules with improved selectivity. Chem. - Asian J. 2016, 11, 474−477. (b) Ahmedova, A.; Mihaylova, R.; Momekova, D.; Shestakova, P.; Stoykova, S.; Zaharieva, J.; Yamashina, M.; Momekov, G.; Akita, M.; Yoshizawa, M. M2L4 coordination capsules with tunable anticancer activity upon guest encapsulation. Dalton Trans. 2016, 45, 13214−13221. (16) Kishi, N.; Li, Z.; Sei, Y.; Akita, M.; Yoza, K.; Siegel, J. S.; Yoshizawa, M. Wide-ranging host capability of a Pd(II)-linked M2L4 molecular capsule with an anthracene shell. Chem. - Eur. J. 2013, 19, 6313−6320. (17) Yamashina, M.; Sartin, M. M.; Sei, Y.; Akita, M.; Takeuchi, S.; Tahara, T.; Yoshizawa, M. Preparation of highly fluorescent hostguest complexes with tunable color upon encapsulation. J. Am. Chem. Soc. 2015, 137, 9266−9269. (18) Yamashina, M.; Sei, Y.; Akita, M.; Yoshizawa, M. Safe storage of radical initiators within a polyaromatic nanocapsule. Nat. Commun. 2014, 5, 4662. (19) Other representative example: Mal, P.; Breiner, B.; Rissanen, K.; Nitschke, J. R. White phosphorus is air-stable within a selfassembled tetrahedral capsule. Science 2009, 324, 1697−1699. (20) Matsuno, S.; Yamashina, M.; Sei, Y.; Akita, M.; Kuzume, A.; Yamamoto, K.; Yoshizawa, M. Exact mass analysis of sulfur clusters upon encapsulation by a polyaromatic capsular matrix. Nat. Commun. 2017, 8, 749. (21) Yamashina, M.; Matsuno, S.; Sei, Y.; Akita, M.; Yoshizawa, M. Recognition of multiple methyl groups on aromatic rings by a polyaromatic cavity. Chem. - Eur. J. 2016, 22, 14147−14150. (22) Yamashina, M.; Akita, M.; Hasegawa, T.; Hayashi, S.; Yoshizawa, M. Polyaromatic nanocapsule as a sucrose receptor in water. Sci. Adv. 2017, 3, No. e1701126. (23) Kusaba, S.; Yamashina, M.; Akita, M.; Kikuchi, T.; Yoshizawa, M. Hydrophilic oligo(lactic acid)s captured by a hydrophobic polyaromatic cavity in water. Angew. Chem., Int. Ed. 2018, 57, 3706−3710. (24) Yamashina, M.; Tsutsui, T.; Sei, Y.; Akita, M.; Yoshizawa, M. A polyaromatic receptor with high androgen affinity. Sci. Adv. 2019, 5, eaav3179. (25) Yamashina, M.; Kusaba, S.; Akita, M.; Kikuchi, T.; Yoshizawa, M. Cramming versus threading of long amphiphilic oligomers into a polyaromatic capsule. Nat. Commun. 2018, 9, 4227. (26) Vasdev, R. A. S.; Preston, D.; Crowley, J. D. Multicavity metallosupramolecular architectures. Chem. - Asian J. 2017, 12, 2513− 2523. (27) Bandi, S.; Pal, A. K.; Hanan, G. S.; Chand, D. K. Stoichiometrically controlled revocable self-assembled ‘spiro’ versus quadruple-stranded ‘double-decker’ type coordination cages. Chem. Eur. J. 2014, 20, 13122−13126. (28) Yazaki, K.; Akita, M.; Prusty, S.; Chand, D. K.; Kikuchi, T.; Sato, H.; Yoshizawa, M. Polyaromatic molecular peanuts. Nat. Commun. 2017, 8, 15914. (29) (a) Yazaki also studied in the Chand group for several months during his Ph.D. course. (b) Prusty, S.; Yazaki, K.; Yoshizawa, M.; Chand, D. K. A truncated molecular star. Chem. - Eur. J. 2017, 23, 12456−12461. (30) Matsumoto, K.; Kusaba, S.; Tanaka, Y.; Sei, Y.; Akita, M.; Aritani, K.; Haga, M.; Yoshizawa, M. A peanut-shaped polyaromatic capsule: solvent-dependent transformation and electronic properties of a non-contacted fullerene dimer. Angew. Chem., Int. Ed. 2019, 58, 8463−8467. (31) Schryver, S. B.; Ramsden, W.; Cross, C. F.; Schidrowitz, P.; Dreaper, W. P.; McBain, J. W.; Turner, T.; Worley, F. P.; Martin, C. J.; Bousfield, W. R.; Morse, H. N.; Henri, V.; Freundlich, H.; The L

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Article

Accounts of Chemical Research Chairman; Ostwald, W.; Chapman, C.; Senter, G. Colloids and their viscosity. Trans. Faraday Soc. 1913, 9, 93−107. (32) (a) Kondo, K.; Suzuki, A.; Akita, M.; Yoshizawa, M. Micellelike molecular capsules with anthracene shells as photoactive hosts. Angew. Chem., Int. Ed. 2013, 52, 2308−2312. (b) Kondo, K.; Klosterman, J. K.; Yoshizawa, M. Aromatic micelles as a new class of aqueous molecular flasks. Chem. - Eur. J. 2017, 23, 16710−16721. (33) Okazawa, Y.; Kondo, K.; Akita, M.; Yoshizawa, M. Polyaromatic nanocapsules displaying aggregation-induced enhanced emissions in water. J. Am. Chem. Soc. 2015, 137, 98−101. (34) Kondo, K.; Suzuki, A.; Akita, M.; Yoshizawa, M. Micellar polyaromatic capsules: enhanced emissive properties through shellfunctionalization. Eur. J. Org. Chem. 2014, 2014, 7389−7394. (35) Okazawa, Y.; Kondo, K.; Akita, M.; Yoshizawa, M. Well-defined aqueous nanoassemblies from amphiphilic meta-terphenyls and their guest incorporation. Chem. Sci. 2015, 6, 5059−5062. (36) Iwasa, J.; Ono, K.; Fujita, M.; Akita, M.; Yoshizawa, M. Switchable trans-cis interconversion of an amphiphilic anthracene trimer. Chem. Commun. 2009, 5746−5748. (37) Suzuki, A.; Kondo, K.; Akita, M.; Yoshizawa, M. Atroposelective self-assembly of a molecular capsule from amphiphilic anthracene trimers. Angew. Chem., Int. Ed. 2013, 52, 8120−8123. (38) Suzuki, A.; Kondo, K.; Sei, Y.; Akita, M.; Yoshizawa, M. A fluorescent molecular capsule with a flexible polyaromatic shell for detecting monoterpene compounds in water. Chem. Commun. 2016, 52, 3151−3154. (39) Nishioka, T.; Kuroda, K.; Akita, M.; Yoshizawa, M. A polyaromatic gemini amphiphile that assembles into a well-defined aromatic micelle with higher stability and host functions. Angew. Chem., Int. Ed. 2019, 58, 6579−6583. (40) Sartin, M. M.; Kondo, K.; Yoshizawa, M.; Takeuchi, S.; Tahara, T. Local environment inside a novel aromatic micelle investigated by steady-state and femtosecond fluorescence spectroscopy of an encapsulated solvatochromic probe. Phys. Chem. Chem. Phys. 2017, 19, 757−765. (41) Kondo, K.; Akita, M.; Nakagawa, T.; Matsuo, Y.; Yoshizawa, M. A V-shaped polyaromatic amphiphile: solubilization of various nanocarbons in water and enhanced photostability. Chem. - Eur. J. 2015, 21, 12741−12746. (42) Origuchi, S.; Kishimoto, M.; Yoshizawa, M.; Yoshimoto, S. A supramolecular approach to preparation of nanographene adlayers using water-soluble molecular capsules. Angew. Chem., Int. Ed. 2018, 57, 15481−15485. (43) Kondo, K.; Akita, M.; Yoshizawa, M. Solubility switching of metallo-phthalocyanines and their larger derivatives upon encapsulation. Chem. - Eur. J. 2016, 22, 1937−1940. (44) Omagari, T.; Suzuki, A.; Akita, M.; Yoshizawa, M. Efficient catalytic epoxidation in water by axial N-ligand-free Mn-porphyrins within a micellar capsule. J. Am. Chem. Soc. 2016, 138, 499−502. (45) Kai, T.; Kishimoto, M.; Akita, M.; Yoshizawa, M. Encapsulation-induced emission enhancement (EIEE) of Eu(III)complexes by aromatic micelles in water. Chem. Commun. 2018, 54, 956−959. (46) Kishimoto, M.; Kondo, K.; Akita, M.; Yoshizawa, M. A pHresponsive molecular capsule with an acridine shell: catch and release of large hydrophobic compounds. Chem. Commun. 2017, 53, 1425− 1428. (47) Catti, L.; Kishida, N.; Kai, T.; Akita, M.; Yoshizawa, M. Polyaromatic nanocapsules as photoresponsive hosts in water. Nat. Commun. 2019, 10, 1948. (48) (a) Very recently, Yoshiyuki Satoh and Dr. Catti developed a redox-active π-stacking capsule using phenothiazine panels. (b) Satoh, Y.; Catti, L.; Akita, M.; Yoshizawa, M. A redox-active heterocyclic capsule: radical generation, oxygenation, and guest uptake/release. J. Am. Chem. Soc. 2019, DOI: 10.1021/jacs.9b03419. (49) Liu, Y.; Hu, C.; Comotti, A.; Ward, M. D. Supramolecular archimedean cages assembled with 72 hydrogen bonds. Science 2011, 333, 436−440.

(50) (a) Mastalerz, M. Shape-persistent organic cage compounds by dynamic covalent bond formation. Angew. Chem., Int. Ed. 2010, 49, 5042−5053. (b) Ono, K.; Iwasawa, N. Dynamic behavior of covalent organic cages. Chem. - Eur. J. 2018, 24, 17856−17868. (c) Acharyya, K.; Mukherjee, P. S. Organic imine cages: molecular marriage and applications. Angew. Chem., Int. Ed. 2019, 58, 8640−8653.

M

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