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A mutually stabilized host-guest pair

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Science Advances  01 Nov 2019:
Vol. 5, no. 11, eaax6707
DOI: 10.1126/sciadv.aax6707

Abstract

By using click chemistry, a hexacationic cage was synthesized. The cage contains two triscationic π-electron–deficient trispyridiniumtriazine (TPZ3+) platforms that are bridged in a face-to-face manner by three ethylene-triazole-ethylene linkers. A diversity of π-electron–rich guests can be recognized within the pocket of the cage, driven by host-guest π-π interactions. The cage cavity acts as a protecting group, preventing an anthracene guest from undergoing Diels-Alder reaction. Under ultraviolet (UV) light, the pyridinium C─N bonds in TPZ3+ platforms are polarized and weakened, resulting in the occurrence of cage decomposition via β-elimination. Guest recognition could help to prevent this UV-stimulated cage decomposition by suppressing the excitation of the TPZ3+ units.

INTRODUCTION

The design and syntheses of macrocyclic molecules in the form of rings (1, 2), cages (3, 4), capsules (5), and some polymeric porous materials (6, 7) have always attracted great interest in the community of supramolecular chemistry. These hosts often have preorganized pockets or cavities, where various guests with complementary geometries and sizes could be accommodated and isolated from the bulk environment. As a consequence, a variety of labile molecules such as cyclobutadiene (8), hemiaminal (9, 10), white phosphorus (1113), benzyne (14), sulfur clusters (15), and iminiums (16) were able to be stabilized. Despite these many examples of the protected guest within a host, the reports of using a guest to stabilize a host are rare, except for a few self-assembled cages (17, 18) containing imine linkages, which become more stable against hydrolysis in aqueous solution when the cage cavities are occupied by hydrophobic guests.

Here, we reported the synthesis of a hexacationic cage molecule via a type of click chemistry, namely, copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC) (19). This cage bears two π-electron–deficient (TPZ3+) platforms that are bridged and separated by three ethylene-triazole-ethylene linkers in a face-to-face manner by approximately 6.7 Å. The cage is able to accommodate a variety of aromatic hydrocarbons including anthracene. The anthracene guest could be protected within the cage cavity from reacting with an alkyne in bulk solution. Using a cage to encapsulate and protect a furan guest from reacting with maleimide was also reported by Smulders and Nitschke (20) years ago. The triazole bridges of the cage were observed to undergo ultraviolet (UV) light–stimulated β-elimination, thanks to the TPZ3+, whose excited state can polarize and weaken the pyridinium C─N bonds. The UV light–stimulated β-elimination reaction could be prevented when a π-electron guest occupies the cage cavity. This is because host-guest π-π interactions efficiently quench or suppress the excitation of the TPZ3+ platforms in the host.

RESULTS AND DISCUSSION

Synthesis of the cage

Two precursors, namely, 13+•3PF6 and 23+•3PF6, which bear either three alkyne or three azide functional groups grafted on a central triscationic TPZ3+ moiety, were synthesized from commercially available compounds in two or three steps, respectively. These two precursors were combined in a 1:1 ratio in acetone in the presence of a Cu(MeCN)4PF6 and tris[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl]amine (TBTA) ligand, which were used to catalyze CuAAC. After stirring the reaction mixture at room temperature for 12 hours, a triangular primatic cage 36+•6PF6 was generated as one of the major products, which was isolated in 24% yield after performing chromatographic purification. 36+•6PF6 was fully characterized by 1H and 13C nuclear magnetic resonance (NMR) spectroscopies, as well as mass spectrometry (see the Supplementary Materials).

Guest recognition ability of the cage

1H NMR spectra recorded in CD3CN reveal that 36+ represents a promising host to accommodate a variety of guests bearing π-electron moieties, including naphthalene, anthracene, phenanthrene, pyrene, triphenylene, perylene, and corannulene, forming a series of inclusion complexes. In the corresponding 1H NMR spectra (Fig. 1), all of the resonances of the bound guests undergo upfield shifts, indicating that the cage cavity provides a shielded magnetic environment for the guests. By using either 1H NMR spectroscopy or isothermal titration calorimetry (ITC), the association constants (Ka) of the corresponding inclusion complexes were determined in MeCN to be 1.9 ± 0.2 × 103, 6.68 ± 0.3 × 104, 81.5 ± 7.3 × 104, 82.2 ± 6.5 × 104, 306 ± 30.9 × 104, 484 ± 62.4 × 104, and 603 ± 91.1 × 104 M─1 for the guests corannulene, naphthalene, anthracene, phenanthrene, pyrene, triphenylene, and perylene, respectively. In general, a guest with a larger π moiety experiences a larger Ka within the cage cavity, given that larger π moieties lead to larger π-electron interactions. This observation is consistent with the results reported by Stoddart in the Excage6+ system (21, 22). The remarkably smaller Ka for corannulene results from its thicker bowl-shaped geometry, which (i) leads to weaker π-π interactions and (ii) makes the corannulene less complementary to fit within the cage cavity. The occurrence of host-guest π-π interactions was convinced by UV-visible (UV-Vis) absorption spectroscopy; i.e., charge-transfer bands were observed (see fig. S15) in the UV-Vis absorption spectra of the corresponding complexes.

Fig. 1 Partial 1H NMR spectra of the cage and its corresponding complexes after recognizing different guests.

Partial 1H NMR spectra (400 MHz, CD3CN, 298 K) of the cage 36+•6PF6 before (A) and after adding 1 eq. of one of the following guests, including (B) corannulene, (C) naphthalene, (D) anthracene, (E) phenanthrene, (F) pyrene, (G) triphenylene, and (H) perylene, forming the corresponding complexes. The Ka values of these complexes were listed, which were measured by either 1H NMR titration for corannulene or ITC in the case of other flat guests. The resonances of the guests are labeled with red arrows.

Diffraction grade single crystals of the inclusion complexes—including anthracene ⊂ 36+, phenanthrene ⊂ 36+, pyrene ⊂ 36+, perylene ⊂ 36+, triphenylene ⊂ 36+, and the “empty” cage 36+ (the counteranions are PF6)—were obtained by vapor diffusion of isopropyl ether into the corresponding MeCN solutions of the complexes or cages, which provided (Fig. 2) unambiguous evidence for the complex formation. The distance between each of the guests and the TPZ3+ platforms are around 3.3 Å, confirming the occurrence of host-guest π-π interactions. The distances between the two TPZ3+ platforms of 36+ are around 6.7 Å, in the case of both “empty” cage and complexes. This consistency convinces our hypothesis that the cage has a preorganized cavity for recognizing the flat aromatic guests.

Fig. 2 Side view of the core structure of the cage and its corresponding supramolecular complexes.

Side view of the core structure of (A) 36+, (B) anthracene ⊂ 36+, (C) phenanthrene ⊂ 36+, (D) pyrene ⊂ 36+, (E) perylene ⊂ 36+, and (F) triphenylene ⊂ 36+, which were obtained from single crystal x-ray diffraction experiments. Carbon, gray; nitrogen, blue; guests, yellow. The disordered solvent molecules, counteranions, and hydrogen atoms are omitted for the sake of clarity.

Guest protection within cage cavity

Within the cavity of 36+, the guests are isolated from the bulk environment, which prevents them from reacting with other substrates in the bulk solutions (Fig. 3A). For example, combining an electron-deficient alkyne 4 (69 mg) and anthracene (0.43 mg) in MeCN (0.6 ml) led to the formation of a Diels-Alder adduct 5, after heating the solution at 80°C for 74 hours. The pseudo–first-order rate constant kobs was determined to be 0.024 s−1 (Fig. 3B, black plot) by using 1H NMR spectroscopy. As a comparison, after encapsulating within the cavity of the cage 36+, the rate of Diels-Alder reaction was significantly decreased. kobs was measured to be 0.0029 s−1 (Fig. 3B, red plot), nearly one order of magnitude smaller than that in the absence of the host. Addition of a competitive guest, namely, pyrene, into the solution of anthracene ⊂ 36+•6PF6 could release anthracene into the bulk solution and turn on the Diels-Alder reaction. In this condition, kobs was measured to be 0.014 s−1 (Fig. 3B, blue plot).

Fig. 3 Evaluation of the ability of the cage to protect an anthracene guest.

(A) Schematic presentation of the Diels-Alder reaction between anthracene and 4 to produce 5 in the absence and presence of 36+. Within the cavity of 36+, the reaction rate of Diels reaction is much slower. When a competitive guest, namely, pyrene, drives the anthracene out from the cage cavity, the Diels-Alder reaction is turned ON. (B) Plots of the ln([A0]/[A]) versus the reaction time by combining anthracene and 200 eq. of 4 in MeCN in the absence of either the cage or pyrene (black trace), in the presence of 1 eq. of 36+ (red trace), and in the presence of both 1 eq. of 36+ and 1.1 eq. of pyrene (blue trace). [A0] and [A] represent the concentration of anthracene in the beginning and at a certain time during reaction, both of which were determined by measuring the integration of a certain proton resonance in the corresponding 1H NMR spectra. The slopes of the three plots represent the apparent pseudo–first-order rate constant (kobs) of the Diels-Alder reaction, which was 0.024, 0.0029, and 0.014 s−1, respectively.

Cage protection via guest accommodation

36+ underwent decomposition via β-elimination during the irradiation of UV light (λmax = 365 nm) for 8 hours (Fig. 4A), yielding 3a5+ as one of the β-elimination adducts, whose formation was convinced by mass spectrometry (fig. S31). Although a similar β-elimination reaction has been reported by Chen and colleagues (23), during which a C─O bond was cleaved, using UV light to stimulate a β-elimination that cleaves a C─N bond without the usage of base has not been reported, to the best of our knowledge.

Fig. 4 UV-stimulated β-elimination of the cage and its control derivatives.

(A) Schematic presentation of the UV-stimulated β-elimination of 36+, which produced 3a5+ and a proton as one of the elimination adducts. When a pyrene guest occupies the cage cavity, β-elimination was prohibited. (B) Structural formulas of a tetracationic macrocycle 64+•4PF6 and three TPZ3+ derivatives 73+•3PF6, 83+•3PF6, and 93+•3PF6. (C) The protons in the β-position with respect to the pyridinium nitrogen atoms in 93+•3PF6 are more acidic, because the negative charge of the corresponding deprotonated anion undergoes delocalization onto the triazole unit.

We reasonably hypothesize that the UV-stimulated decomposition of 36+ was initiated by activating the TPZ3+ platforms in the cage into an excited state. This excited state of triazine, which contains a singly occupied HOMO (highest occupied molecular orbital), is more electron-withdrawing than its ground state. As a consequence, one of the pyridinium C─N bonds becomes more polarized and therefore weakened for cleavage. This proposition was supported by the following experiments. First, we observed that a macrocycle 64+∙4PF6 (Fig. 4B) containing two bipyridinium moieties was relatively stable and did not undergo β-elimination upon irradiation with UV light for no less than 12 hours (see fig. S38D). This observation indicates that a triazine, which acts as a photosensitizer to polarize the C─N bonds, plays an important role in β-elimination. Second, a TPZ3+ derivative, namely, 73+∙3PF6 (Fig. 4B), underwent reduction into its radical state under the protection of an atmosphere of nitrogen, namely, 7(2+)•, after irradiating 73+∙3PF6 with UV light in the presence of either methanol or tetrahydrofuran (THF) as a sacrificial reagent, as inferred from the corresponding electron paramagnetic resonance (EPR) spectrum (Fig. 5B, red trace). Note that without UV light, neither methanol nor THF is capable of reducing 73+ to 7(2+)•. These observations indicate that TPZ3+ becomes more oxidative or electron-withdrawing in its excited state. This behavior is reminiscent of a few other π-electron acceptors such as naphthalene-1,8:4,5-bis(dicarboximide) (24) and 2,4,6-triphenylpyrylium (25), both of which also become more oxidative in their UV light–stimulated excited state. Last, it seems that the occurrence of β-elimination requires relatively acidic β-protons in the methylene unit with respect to the pyridinium nitrogen atom. This hypothesis is proven by the observation that upon irradiation of three TPZ3+ derivatives including 73+•3PF6, 83+•3PF6, and 93+•3PF6 with UV light, only 93+•3PF6 underwent decomposition, yielding β-elimination products 9a2+ and 9b2+ (see figs. S33 to S36 and S38), as well as the alkene fragment S3 (see its molecular formula in fig. S37). The β-protons in 93+ is more acidic than those in 73+ and 83+, given that the negative charge of its deprotonated anionic form can be delocalized onto the electro-withdrawing triazole moiety (Fig. 4C). It seems that under UV light, a few other reactions besides β-elimination also occurred, which precluded our trial to calculate the yield of β-elimination of 36+. For example, under UV light, the alkene S3 underwent oxidation, leading to the generation of an aldehyde S4 (see its molecular formula in fig. S37).

Fig. 5 Mechanism investigation of the cage protection via guest accommodation.

(A) Second scans of the cyclic voltammograms (CVs) for 36+•6PF6 (black trace) and pyrene ⊂ 36+•6PF6 (red trace). The reduction peak observed at −0.058 V corresponds to the reduction process of a reference compound, namely, ferrocene/ferrocene+ (Fc/Fc+). All the CVs were recorded under the same conditions of temperature (298 K), solvent (argon-purged MeCN), concentrations (1 mM), and tetrabutylammonium hexafluorophosphate electrolyte (0.1 M). The scan rate was set at 200 mV s−1. (B) EPR spectra of 73+•3PF6 under the irradiation of UV light at 365 nm in the presence of THF as a sacrificial reductant in the absence (red trace) and in the presence of 8 eq. of pyrene (blue trace). The EPR signal of the red trace indicates the formation of 7(2+)• radical. The black trace corresponds to a solution of 7(2+)•, which was produced by adding Zn dust as a reductant into a MeCN solution of 73+•3PF6. (C) Time-resolved absorption spectra of 36+•6PF6 (red trace) and pyrene ⊂ 36+•6PF6 (blue trace) upon stimulation by UV light at 365 nm. a.u., arbitrary units.

When the cavity of 36+ was occupied by a guest such as anthracene, phenanthrene, pyrene, and triphenylene, the UV light–stimulated cage decomposition was avoided; i.e., no appreciable decomposition was observed (figs. S39 and S40) after irradiating the complex for no less than 12 hours. This is because the guest molecule introduces π-π interactions, which could prevent or suppress the UV-stimulated excitation of TPZ3+ units. This proposition is supported by the following experiments.

First, cyclic voltammograms of 36+•6PF6 (Fig. 5A, black trace) and pyrene ⊂ 36+•6PF6 (Fig. 5A, red trace) were recorded in MeCN. One of the two TPZ3+ units in the complex pyrene ⊂ 36+•6PF6 has a more negative reduction potential, i.e., −730 mV, compared to −635 mV in the case of empty cage. The implication is that the LUMO (lowest unoccupied molecular orbital) of TPZ3+ is increased by 0.095 eV and that the compound becomes more difficult to reduce when it undergoes π-π interactions with a pyrene guest. The increase of LUMO of the TPZ3+ thus results in the failure or difficulty of generating the excited state, as a consequence of which, β-elimination did not occur. Second, high-energy excited state decay kinetics for 36+•6PF6 in the absence and presence of a pyrene guest at UV light excitation (365 nm) were probed by transient absorption spectra (Fig. 5C and fig. S42). It is obvious that the excited state of the TPZ3+ units in the complex pyrene ⊂ 36+•6PF6 (Fig. 5C, blue trace) decays much faster to ground state (~15 ps) compared to those of the cage 36+•6PF6 itself (~ 170 ps) (Fig. 5C, red trace), likely suppressing the deposition process in the former. Third, π-π interactions were observed to prevent the UV light–stimulated reduction of 73+; i.e., irradiation of 73+ with UV light (λmax = 365 nm) in the presence of 8 eq. of pyrene and a sacrificial reductant did not produce the radical 7(2+)•, as inferred from the corresponding silent EPR spectrum (Fig. 5B, blue trace). These experiments all help to convince that host protection was accomplished by means of host-guest π-electron donor-acceptor interactions that suppress the UV light–stimulated excitation of TPZ3+.

CONCLUSION

In summary, we synthesized a hexacationic cage by means of click reaction. This cage has a preorganized cavity for recognizing a variety of aromatic guests, including anthracene and pyrene. On one hand, the cage acts as a molecular container, which isolates anthracene from bulk environment and therefore protects it from undergoing Diels-Alder reaction. On the other hand, the triazole bridges in the cage undergo β-elimination under UV light irradiation, during which the TPZ3+ units in the cage could be activated into their excited state and promote the cleavage of C─N bonds. Because a guest such as pyrene could introduce π-π donor-acceptor interactions that quenched or suppressed the UV light–stimulated excited state of TPZ3+, host protection could thus be achieved by guest recognition. The use of small molecular components to block the reaction pathway of a large system and influence its properties will likewise be developed.

MATERIALS AND METHODS

All reagents and solvents were purchased from commercial sources and used without further purification. Solvents were deoxygenated by passing N2 through the solvent for 30 min. Manipulations were performed under a normal laboratory atmosphere unless otherwise noted. 73+•3PF6−S1, S12+•2PF6− S2, and S22+•2PF6− S3 were synthesized as previously reported. NMR spectra were recorded at ambient temperature using Bruker AVANCE III 400/500 or Agilent DD2 600 spectrometers, with working frequencies of 400, 500, and 600 MHz and 100, 125, and 150 MHz for 1H and 13C, respectively. Chemical shifts are reported in parts per million (ppm) relative to the residual internal nondeuterated solvent signals (CD3CN, δ = 1.94 ppm; CDCl3, δ = 7.27 ppm). High-resolution mass spectra (HRMS) were measured using a Shimadzu liquid chromatography–mass spectrometry ion trap time-of-flight instrument. X-ray crystallographic data were collected on a Bruker D8 Venture diffractometer. ITC experiments were performed on a MicroCal system, VP-ITC model. EPR spectra were taken on a continuous-wave EPR spectrometer (Bruker A300), and the samples were injected into a glass capillary and put into the cavity. The EPR spectra were recorded in X-band at room temperature with a microwave power of 0.2 mW, a modulation frequency of 100 kHz, and a modulation amplitude of 1 G. The g factors were corrected with respect to that of an equipped g marker (1,1-diphenyl-2-picrylhydrazyl, g = 2.0036). UV-Vis-NIR absorption spectra were taken on a Cary Series UV-Vis-NIR spectrophotometer.

SUPPLEMENTARY MATERIALS

Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/11/eaax6707/DC1

Scheme S1. Synthesis of 13+·3PF6.

Scheme S2. Synthesis of 23+·3PF6.

Scheme S3. Synthesis of 36+·6PF6.

Scheme S4. Synthesis of 64+·4PF6.

Scheme S5. Synthesis of 83+·3PF6.

Scheme S6. Synthesis of 93+·3PF6.

Fig. S1. 1H and 13C spectrum of 36+·6PF6.

Fig. S2. 1H-1H correlation spectroscopy (500 MHz, D2O, 298 K) spectrum of 36+·6PF6.

Fig. S3. Electrospray ionization–HRMS of 36+·6PF6.

Fig. S4. 1H and 13C spectrum of 64+·4PF6.

Fig. S5. 1H-1H correlation spectroscopy spectrum (500 MHz, D2O, 298 K) of 64+·4PF6.

Fig. S6. Electrospray ionization–HRMS of 64+·4PF6.

Fig. S7. 1H NMR spectrum (400 MHz, CD3CN, 298 K) of 36+·6PF6 (1.34 mM) upon addition of different amount of anthracene.

Fig. S8. 1H NMR spectrum (400 MHz, CD3CN, 298 K) of 36+·6PF6 (1.34 mM) upon addition of different amount of phenanthrene.

Fig. S9. 1H NMR spectrum (400 MHz, CD3CN, 298 K) of 36+·6PF6 (1.34 mM) upon addition of different amount of pyrene.

Fig. S10. 1H NMR spectrum (400 MHz, CD3CN, 298 K) of 36+·6PF6 (1.34 mM) upon addition of different amount of triphenylene.

Fig. S11. 1H NMR spectrum (400 MHz, CD3CN, 298 K) of 36+·6PF6 (1.34 mM) upon addition of different amount of corannulene.

Fig. S12. 1H NMR spectrum (400 MHz, CD3CN, 298 K) of the mixture of 76+·3PF6 (1.34 mM) and 6eqiv of corannulene and 76+·3PF6 (1.34 mM).

Fig. S13. Plot of the upfield shifts of the resonance of proton e (assigned in fig. S11) of 36+·6PF6.

Fig. S14. UV-Vis absorption spectrum of 36+·6PF6 at 0.5 μM in MeCN at 298 K.

Fig. S15. UV-Vis absorption spectra of polycyclic aromatic hydrocarbon (PAH) guests, 36+·6PF6, and the corresponding 1:1 complexes in MeCN at 298 K.

Fig. S16. Fluorescence spectra of the 36+·6PF6 (1 × 10−3 mM) after addition of different equivalents of PAH guests.

Fig. S17. Titration plots (heat rate versus time and heat versus guest/host ratio) obtained from ITC experiments of 36+·6PF6 (0.1 mM, 1.4 ml) with naphthalene (2 mM, 0.4 ml) in CH3CN (298 K).

Fig. S18. Titration plots (heat rate versus time and heat versus guest/host ratio) obtained from ITC experiments of 36+·6PF6 (0.1 mM, 1.4 ml) with anthracene (2 mM, 0.4 ml) in CH3CN (298 K).

Fig. S19. Titration plots (heat rate versus time and heat versus guest/host ratio) obtained from ITC experiments of 36+·6PF6 (0.1 mM, 1.4 ml) with phenanthrene (2 mM, 0.4 ml) in CH3CN (298 K).

Fig. S20. Titration plots (heat rate versus time and heat versus guest/host ratio) obtained from ITC experiments of 36+·6PF6 (0.1 mM, 1.4 ml) with pyrene (2 mM, 0.4 ml) in CH3CN (298 K).

Fig. S21. Titration plots (heat rate versus time and heat versus guest/host ratio) obtained from ITC experiments of 36+·6PF6 (0.1 mM, 1.4 ml) with triphenylene (2 mM, 0.4 ml) in CH3CN (298 K).

Fig. S22. Titration plots (heat rate versus time and heat versus guest/host ratio) obtained from ITC experiments of 36+·6PF6 (0.1 mM, 1.4 ml) with perylene (2 mM, 0.4 ml) in CH3CN (298 K).

Fig. S23. Titration plots (heat rate versus time and heat versus guest/host ratio) obtained from ITC experiments of 36+·6PF6 (0.1 mM, 1.4 ml) with corannulene (2 mM, 0.4 ml) in CH3CN (298 K).

Fig. S24. 1H NMR spectra (500 MHz, CD3CN, 298 K) of a 1:100 mixture of anthracene and 4 recorded by heating the mixture at 343 K for a certain amount of time.

Fig. S25. 1H NMR spectra (500 MHz, CD3CN, 298 K) of a 1:150 mixture of anthracene and 4 recorded by heating the mixture at 343 K for a certain amount of time.

Fig. S26. 1H NMR spectra (500 MHz, CD3CN, 298 K) of a 1:200 mixture of anthracene and 4 recorded by heating the mixture at 343 K for a certain amount of time.

Fig. S27. 1H NMR spectra (500 MHz, CD3CN, 298 K) of a 1:1:200 mixture of anthracene, 36+·6PF6, and 4, which were recorded by heating the mixture at 343 K for a specific amount of time.

Fig. S28. 1H NMR spectra (500 MHz, CD3CN, 298 K) of a 1:1:1.1:200 mixture of anthracene, 36+·6PF6, pyrene, and 4, which were recorded by heating the mixture at 343 K for a specific amount of time.

Fig. S29. Plots of −ln([A]/[A0]) versus reaction time of the Diel-Alder reactions of anthracene and the alkyne 4 in different reaction conditions.

Fig. S30. 1H NMR spectra (500 MHz, CD3CN, 298 K) of 36+·6PF6 after irradiating the sample with UV light (λmax = 365 nm) for a special amount of time.

Fig. S31. ESI-HRMS of a solution of 36+·6PF6 in MeCN, upon irradiation with UV light (λmax = 365 nm) for 8 hours.

Fig. S32. ESI-MS of a solution of 36+·6PF6 in MeCN, upon irradiation with UV light (λmax = 365 nm) for a special amount of time.

Fig. S33. 1H NMR spectra (500 MHz, CD3CN, 298 K) of 93+·3PF6 after irradiating the sample with UV light (λmax = 365 nm) for a special amount of time.

Fig. S34. ESI-HRMS of a solution of 93+·3PF6 in MeCN, upon irradiation with UV light (λmax = 365 nm) for 8 hours.

Fig. S35. ESI-MS of a solution of 93+·3PF6 in MeCN, upon irradiation with UV light (λmax = 365 nm) for a special amount of time.

Fig. S36. 1H NMR spectrum (500 MHz, CD3CN, 298 K) of 9a2+·2PF6, which was obtained from the UV light irradiation reaction mixture (used for fig. S33) by means of chromatographic purification.

Fig. S37. 1H NMR spectra (500 MHz, CD3CN, 298 K) of the solution containing S3 and S4.

Fig. S38. Partial 1H NMR spectra (400 MHz, CD3CN, 298 K) of 73+·3PF6, 64+·4PF6, and 83+·3PF6, before and after UV light irradiation (λmax = 356 nm).

Fig. S39. 1H NMR spectra (500 MHz, CD3CN, 298 K) of a complex pyrene ⊂ 36+·6PF6 after the sample was irradiated under UV light (λmax = 365 nm) for a special amount of time.

Fig. S40. Partial 1H NMR spectra (400 MHz, CD3CN, 298 K) of 36+·6PF6 under UV light (λmax = 365 nm) in the presence of 1.1 eq. of PAH guests.

Fig. S41. Partial 1H NMR spectra of 93+·3PF6 under UV light (λmax = 365 nm) for 12 hours in the presence of different equivalents of pyrene.

Fig. S42. Transient absorption spectra of 36+·6PF6 and pyrene ⊂ 36+·6PF6 under UV light excitation.

Fig. S43. Different views of the solid-state structure of 36+·6PF6.

Fig. S44. Different views of the solid-state structure of anthracene ⊂ 36+·6PF6.

Fig. S45. Different views of the solid-state structure of phenanthrene ⊂ 36+·6PF6.

Fig. S46. Different views of the solid-state structure of pyrene ⊂ 36+·6PF6.

Fig. S47. Different views of the solid-state structure of triphenylene ⊂ 36+·6PF6.

Fig. S48. Different views of the solid-state structure of perylene ⊂ 36+·6PF6.

Table S1. Ka values and thermodynamic parameters for the 1:1 complexes formed between 36+·6PF6 and PAH guests in MeCN at 25°C.

References (2631)

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REFERENCES AND NOTES

Acknowledgments: Funding: This work was supported by the National Natural Science Foundation of China (nos. 91856116 and 21772173), the Natural Science Foundation of Zhejiang Province (no. LR18B020001), and “the Fundamental Research Funds for the Central Universities” (no. 2019FZA3007). Author contributions: C.Z. and Hao Li designed experiments. C.Z., H.W., J.Z., Y.L., R.D., Y. Zhang, L.S., T.J., and Y. Zhu performed experiments. C.Z. and Hao Li wrote the manuscript. H.Z., Haoran Li, and Hao Li edited the manuscript. Competing interests: The authors declare that they have no competing interests. Data and materials availability: All data needed to evaluate the conclusions in the paper are present in the paper and/or the Supplementary Materials. Additional data related to this paper may be requested from the authors.
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