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[Kazuki Shiga](https://orcid.org/0009-0002-4889-7163), Ryota Yamazaki, [Hajime Shigemitsu](https://orcid.org/0000-0002-3104-049X), [Yuuya Nagata](https://orcid.org/0000-0001-5926-5845), [Norimitsu Tohnai](https://orcid.org/0000-0001-7051-7599)

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[Supramolecular Protection–Deprotection for Switching Pore‐Surface Functionality in a Crystalline Porous Organic Salt](https://mdr.nims.go.jp/datasets/7c31f02e-d8fe-4607-87a6-ac891bc812a2)

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Angewandte Chemie International EditionHow to cite: Angew. Chem. Int. Ed. 2026, 65, e1547062doi.org/10.1002/anie.1547062RESEARCH ARTICLESupramolecular Protection–Deprotection for SwitchingPore-Surface Functionality in a Crystalline Porous OrganicSaltKazuki Shiga1Ryota Yamazaki1Hajime Shigemitsu2Yuuya Nagata2Norimitsu Tohnai11Department of Applied Chemistry, Graduate School of Engineering, The University of Osaka, Suita, Osaka, Japan2Research Center for Macromolecules andBiomaterials (RCMB), National Institute for Materials Science (NIMS), Tsukuba, Ibaraki, JapanCorrespondence: Norimitsu Tohnai ()Received: 10 May 2026Revised: 2 July 2026Accepted: 21 July 2026Keywords: crystal engineering hydrogen bonds microporous materials phase transitions supramolecular chemistryABSTRACTThe precise installation of highly interactive functional groups on pore surfaces remains a central challenge in crystalline porousmaterials since such groups often interfere with framework formation. In this study, supramolecular protection–deprotectionwas performed in a porous organic salt that temporally separated framework construction from the emergence of pore-surfacefunctionality. During crystallization, the phenolic OH groups were protected by hydrogen bonding with dimethyl sulfoxide(DMSO), enabling the formation of a crystalline framework based on charge-assisted hydrogen bonds. Stepwise removal of DMSOinduced a two-step single-crystal-to-single-crystal phase transition, affording first a dormant state (Form II), in which the OHgroups remained protected, and subsequently an active state (Form III), in which the OH groups were exposed on the pore surfacetogether with the emergence of porosity. The dormant state was re-formed by exposure to DMSO or N,N-dimethylacetamide vapor,whereas other solvents failed to induce the same structural response. In contrast, the active state showed markedly enhancedNH3 uptake relative to the dormant state and preferential adsorption of NH3 over CO2, N2, H2, and O2 under the investigatedconditions. These results demonstrate that supramolecular protection–deprotection provides a useful strategy for temporallycontrolling pore-surface functionality in dynamic crystalline porous materials.1IntroductionIeapaootian crystalline porous materials, the molecular recognition prop-rties of pore surfaces are strongly governed by the type andrrangement of functional groups exposed within the pores,articularly on the pore surfaces [1–12]. Therefore, the regularnd accessible installation of highly interactive functional groupsn pore surfaces represents a central challenge in the designf functional porous materials. Specifically, functional groupshat promote guest interactions tend to participate stronglyn the intermolecular interactions that govern crystallizationnd framework formation [3, 13–17]. Consequently, they caneither interfere with the formation of the desired framework orbecome embedded into the internal bonding network instead ofbeing exposed on the pore surface. This problem is particularlypronounced for phenolic OH groups, whose acidity and stronghydrogen-bonding ability render them attractive for molecularrecognition but also make them highly prone to interveningin structure formation itself [18], thereby hindering their selec-tive placement on the pore surface of an ordered crystallineframework.To address this issue, post-synthetic modification (PSM), in whichfunctional-group transformation is performed after frameworkTohis is an open access article under the terms of the Creative Commons Attribution Licenriginal work is properly cited.se, which permits use, distribution and reproduction in any medium, provided the©2026 The Author(s). Angewandte Chemie International Edition published by Wiley-VCHGmbH.Angewandte Chemie International Edition, 2026; 65:e1547062tohnai@chem.eng.osaka-u.ac.jp | | | | https://doi.org/10.1002/anie.15470621 of 11https://doi.org/10.1002/anie.1547062https://orcid.org/0009-0002-4889-7163https://orcid.org/0000-0002-3104-049Xhttps://orcid.org/0000-0001-7051-7599mailto:tohnai@chem.eng.osaka-u.ac.jphttp://creativecommons.org/licenses/by/4.0/https://doi.org/10.1002/anie.1547062http://crossmark.crossref.org/dialog/?doi=10.1002%2Fanie.1547062&domain=pdf&date_stamp=2026-08-05csfpirratHsftpObTaast[tIfbssgtassgncsf–onstruction, has been extensively developed [19–21]. However,ince PSM relies on covalent transformation, it can sufferrom several limitations, including damage to crystallinity ororosity, heterogeneous or incomplete solid-state reactions, andncreased design complexity arising from the need to pre-installeactive sites [19–24]. Accordingly, a new design strategy isequired that enables pore-surface functionality to be generatednd controlled after crystallization without relying on covalentransformation.ere, we develop a supramolecular protection–deprotectiontrategy that addresses this challenge by temporarily renderingunctional groups dormant during crystallization and releasingheir function after framework formation. Specifically, in aorous organic salt (POS) bearing phenolic OH groups, theH groups are supramolecularly protected through hydrogenonding with dimethyl sulfoxide (DMSO) during crystallization.his decoupled the OH groups from framework formation whilellowing construction of a crystalline framework through charge-ssisted hydrogen bonds (CAHBs) between ammonium ions andulfonate groups [13–16, 25–28]. Subsequent heating induced awo-step single-crystal-to-single-crystal (SCSC) phase transition9, 29–34] and afforded a dormant state (Form II), in whichhe OH groups are protected, followed by an active state (FormII), in which the OH groups are exposed on the pore sur-ace. This strategy is designed to achieve temporal separationetween framework construction and the emergence of pore-urface functionality by using reversible hydrogen-bond-basedupramolecular interactions rather than covalent protecting-roup chemistry. Reformation of the dormant state by exposureo specific solvent vapors demonstrated both one-way activationnd reversible control over the functional state of the poreurface [35]. Furthermore, ammonia (NH3) adsorption mea-urements revealed that the active state, in which the OHroups were exposed on the pore surface, exhibited a pro-ounced preference for NH3, an important target for selectiveapture and recovery [36–43]. Comparison with the dormanttate further demonstrated that this NH3-responsive adsorptionunction can be switched through supramolecular protectiondeprotection.2Results and Discussion2T.1 Structural Design and Stepwise SCSCransformation2D.1.1 Supramolecular Protection of the OH Groups byMSOBptaSswtFaiased on a supramolecular functional group protection strategy, aorous organic salt was designed from 2′,5′-dihydroxy-[1,1′:4′,1″-erphenyl]-4,4″-disulfonic acid (HQDPS), a phenolic disulfoniccid bearing two OH groups, and tert-butylamine (tBuA) (Figures1–S5). Recrystallization of the resulting crude HQDPS/tBuAalts from DMSO afforded Form I, in which the OH groupsere preferentially hydrogen-bonded to DMSO molecules andherefore did not participate in framework construction (Figure 1,igures S6–S7, Table S1) [44]. Instead, the framework itself wasssembled through charge-assisted hydrogen bonds (CAHBs),n which the ammonium cation (tBuAH+) acted as the protondonor and the sulfonate group as the proton acceptor. Specifi-cally, the phenolic OH groups were preferentially captured byDMSO and were thus effectively excluded from CAHB networkformation, resulting in the selective formation of Form I. There-fore, DMSO serves as both a recrystallization solvent and aprotecting molecule that temporarily isolates the OH groups fromframework formation [45].This interpretation was supported by comparison with a controlexperiment performed using methanol. During recrystallizationfrom methanol, the OH groups directly formed hydrogen bondswith the sulfonate groups, yielding a crystal structure in whichthe OH groups were incorporated into the internal framework(Figure 1 and Figure S8). Thus, under conditions in which the OHgroups remained unprotected by DMSO, they again participatedin framework formation. Accordingly, Form I should not beviewed simply as a crystal phase obtained in the presence ofDMSO, but rather as the outcome of supramolecular protectionby DMSO, which separates the CAHB network responsible forframework construction from the OH groups that serve asfunctional sites. These results indicate that temporary protectionof a specific functional group can separate its role in frameworkformation from its role as a functional site.Subsequently, heat treatment of Form I induced a two-step SCSCphase transition accompanied by the stepwise removal of DMSOand progressive deprotection of the OH groups. Thus, aftercrystallization in a state where the OH groups were temporarilydecoupled from framework formation, the system passed througha dormant state (Form II) while retaining crystallinity, ultimatelyaffording an active state (Form III) in which the OH groups wereexposed on the pore surface. This behavior clearly confirms thatthe present strategy achieves temporal separation between therole of the OH groups in framework construction and their roleas functional pore-surface sites.To further support the interpretation that DMSO acts asa supramolecular protecting molecule for the phenolic OHgroups, we also examined a methoxy-substituted analogue,TPDS-OMe2/tBuA, in which the phenolic OH groups arecovalently masked as methoxy groups. Recrystallization ofTPDS-OMe2/tBuA under conditions similar to those used forHQDPS/tBuA afforded two crystalline polymorphs that werestructurally related to HQDPS/tBuA Form I (Figure S9). Inboth structures, DMSO molecules were hydrogen-bonded to thetBuAH+ cations, and the sulfonate–ammonium charge-assistedhydrogen bonds formed a one-dimensional ladder-type network.Thus, the DMSO-protected state of HQDPS/tBuA is structurallyanalogous to a covalently O-methyl-masked state, supporting theassignment of DMSO as a supramolecular protecting molecule forthe phenolic OH groups.2.1.2 First SCSC Step: Selective Removal of DMSOHydrogen-Bonded to the tBuAH+ CationsUpon heating Form I at 100◦C for 1 h, the DMSO moleculeshydrogen-bonded to the ammonium cations (tBuAH+) wereselectively removed, while those hydrogen-bonded to the OHgroups were retained, resulting in conversion to Form II (Figure 2,15213773, 2026, 40, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/anie.1547062 by National Institute For, Wiley Online Library on [09/10/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OAarticles are governed by the applicable Creative Commons License2of 11Angewandte Chemie International Edition, 2026imageFIGURE 1 Schematic illustration of the present design strategy and comparison with the structure obtained from methanol recrystallization.imageFIGURE 2 Two-step SCSC phase transition induced by the stepwise removal of DMSO. Structural transformation from Form I to the dormantstate Form II and then to the active state Form III, together with the accompanying reorganization of the CAHB network.TmeegtrwcistStIrTx(cable S1). Structural analysis confirmed that the multiple DMSOolecules present in Form I were not equivalent; rather, theyxhibited distinct behavior depending on their local bindingnvironments. Concomitantly, the CAHB network was reor-anized from a one-dimensional (1D) ladder structure into awo-dimensional (2D) sheet structure (Figure 2). Additionally,emoval of the DMSO molecules hydrogen-bonded to tBuAH+,hich occupied the space between the 1D hydrogen-bondedhains, promoted rearrangement of the sulfonate–ammoniumnteractions, leading to expansion of the network from a 1Dtructure in Form I to a 2D structure in Form II. In contrast,he OH groups remained protected by DMSO. Therefore, the firstCSC transformation should be regarded not as deprotection ofhe OH groups, but as the formation of the dormant state (FormI), in which the OH groups remain protected while structuraleorganization proceeds.his interpretation was also supported at the bulk level by powder-ray diffraction (PXRD) and thermogravimetric analysis (TGA)Figure 3). Specifically, Form II exhibited a diffraction patternlearly distinct from that of Form I and in good agreementwith the simulated pattern, demonstrating that the first heatingstep generated a single new phase (Figure 3a). In TGA, thelow-temperature weight-loss component observed for Form I dis-appeared in Form II, consistent with the partial removal of DMSOduring the first heating step (Figure 3b). Taken together, theseresults confirm that, in the first SCSC step, DMSO moleculesoccupying the interlayer space of the 1D ladder-type CAHBnetwork were selectively removed while the OH groups remainedprotected to afford the dormant state Form II.2.1.3 Second SCSC Step: Removal of the OH-ProtectingDMSO MoleculesUpon further heating Form II at 160◦C for 1 h, the DMSOmolecules protecting the OH groups were removed, yieldingForm III (Table S1), wherein the OH groups were exposed on thepore surface (Figure 2). In this second structural transformation,the OH–DMSO interactions retained in Form II were disrupted,and the previously protected OH groups became exposed for thefirst time. This step therefore corresponds not merely to residual15213773, 2026, 40, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/anie.1547062 by National Institute For, Wiley Online Library on [09/10/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OAarticles are governed by the applicable Creative Commons LicenseAngewandte Chemie International Edition, 20263 of 11imageFIGURE 3 Bulk characterization of each activation stage. (a) Experimental and simulated PXRD patterns of Forms I–III. (b) TGA curves of FormsI–III.sbNercgsFafvcIatraITaoaccor(hsltolvent removal but also to a structural transition accompaniedy the emergence of functional sites.otably, this deprotection step was accompanied by a morextensive framework reorganization. As shown in Figure 2,emoval of the DMSO molecules protecting the OH groupsaused substantial rotation and displacement of the sulfonateroups, and the CAHB network changed from the 2D sheettructure of Form II to the three-dimensional (3D) network oform III. Consequently, Form III exhibited 1D channels withn apparent aperture of approximately 6.7 × 4.0 Å, as estimatedrom the final crystallographic dataset. The solvent-accessibleoid volume calculated using PLATON was 294.8 Å3 per unit cell,orresponding to a void fraction of 17.3%. The porosity of FormII should therefore be understood not as arising from simplectivation of pre-existing voids, but as being generated throughhe second SCSC step, which completes OH deprotection andeorganizes the entire crystal. Details of the pore-size evaluationnd gas-sorption-derived analysis are provided in the Supportingnformation.his interpretation was again supported by the bulk PXRDnd TGA results (Figure 3). Specifically, the diffraction patternbtained for Form III clearly differed from that of Form IInd was in good agreement with the simulated pattern, indi-ating that the second heating step generated another newrystal structure (Figure 3a). In TGA, the weight-loss componentbserved for Form II disappeared in Form III, consistent with theemoval of the remaining DMSO during the second heating stepFigure 3b). Notably, despite the large molecular displacements,igh crystallinity was maintained in Form III. This observationuggests that the structural transformation proceeds not throughocal collapse but via a cooperative reorganization extendinghroughout the crystal [46, 47].2E.2 Reverse Phase Transition Induced by Vaporxposure and Supramolecular Reprotection2.2.1 Reprotection of the OH Groups by DMSO VaporUppon exposure to DMSO vapor, Form III underwent a reversehase transition to Form II, even at ∼25◦C [48]. Specifically, whenbulk crystals of Form III were exposed to DMSO vapor at ∼25◦Cfor 24 h, the PXRD pattern became consistent with the simulatedpattern for Form II, indicating structural conversion from FormIII to Form II (Figure 4a). This result shows that the active stateobtained by thermal activation can respond to a mild stimulussuch as solvent vapor while retaining crystallinity.This transformation was also supported by TGA. After exposureto DMSO vapor, a new weight-loss feature appeared at ∼150◦C,which was absent in Form III before vapor exposure (Figure 4b).This behavior was consistent with the TG profile of Form IIshown in Figure 3b, suggesting that DMSO vapor exposure didnot merely lead to surface adsorption of the solvent but ratherre-formed the dormant state containing DMSO. Taken together,the PXRD and TGA results indicate that this vapor responseshould be understood not as simple DMSO uptake by Form III,but as a structural transformation to Form II accompanied byreprotection of the OH groups.Notably, this vapor-induced reprotection (Form III → Form II)and thermally induced deprotection (Form II → Form III) wererepeatedly observed over at least three cycles (Figure 4a). Aftereach cycle, the PXRD patterns retained the characteristic peaksof Forms II and III, respectively, without any marked loss ofcrystallinity. These results demonstrate that the dormant andactive states can be reversibly interconverted in response toDMSO vapor and heat [35]. Thus, the present system enablesreversible switching between dormant and active pore-surfacestates through repeated protection–deprotection.2.2.2 Selectivity of the Reprotecting MoleculesThe phase transition from Form III to Form II showed clearselectivity toward specific vapor molecules. Upon exposure ofForm III to acetone, 2-propanol, N,N-dimethylformamide (DMF),and N,N-dimethylacetamide (DMA) vapor under conditions anal-ogous to those used for DMSO (Figure 4c), only DMA inducedstructural conversion to Form II, whereas no pronounced phasetransitions were observed for the other solvents (Figure 4d). Thisresult demonstrates that Form III exhibits structural responseonly to limited guest molecules.15213773, 2026, 40, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/anie.1547062 by National Institute For, Wiley Online Library on [09/10/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OAarticles are governed by the applicable Creative Commons License4of 11Angewandte Chemie International Edition, 2026imageFIGURE 4 Vapor-induced reprotection and molecular selectivity of the reverse phase transition. (a) PXRD patterns showing DMSO-vapor-inducedreprotection (Form III → Form II) and thermal deprotection (Form II → Form III) over three cycles. (b) TGA curves of Form III before and after exposureto DMSO vapor. (c) Candidate molecules for supramolecular reprotection together with their Gutmann donor numbers. (d) PXRD patterns of Form IIIafter exposure to various solvent vapors.TabDrs5faetTtwwDptesaFhe selectivity is likely related to the electron-pair-donatingbility of the reprotecting molecules, namely, their hydrogen-ond acceptor ability toward the phenolic OH groups. Indeed,MSO and DMA, both of which induced reprotection, possesselatively high donor numbers (Figure 4c) and can act astrong hydrogen-bond acceptors for phenolic OH groups [49,0]. In contrast, no structural transformation was observedor molecules with lower donor numbers, such as 2-propanolnd acetone. This trend suggests that a certain level oflectron-pair-donating ability is involved in triggering reprotec-ion.his interpretation was further supported by recrystallization ofhe HQDPS/tBuA salt from DMA. The resulting crystal structureas closely related to Form II, and the phenolic OH groupsere supramolecularly protected through hydrogen bonding withMA (Figure S12). Thus, DMA can also act as a supramolecularrotecting molecule for the phenolic OH groups, consistent withhe DMA-induced reprotection observed in the vapor-exposurexperiment. This comparison also indicates that DMA mainlytabilizes a Form II-like reprotected state rather than reproducingll the local interactions characteristic of the DMSO-containingorm I.Interestingly, DMF did not induce structural conversion toForm II despite having a donor number close to that of DMA(Figure 4d). Therefore, although an effective boundary mayexist between DMA and DMF in terms of the ability to inducereprotection, the present response cannot be explained solely bydonor number. In other words, for a reprotecting molecule toinduce conversion to Form II, both sufficient hydrogen-bond-accepting ability and local compatibility with the interactionsites remaining on the pore surface after deprotection appearnecessary.The observed selectivity toward reprotecting molecules is impor-tant from the perspective of both material function and designstrategy. The fact that Form III distinguishes between selectivereprotection and simple guest uptake and undergoes a phasetransition to the dormant state (Form II) only in response tospecific molecular inputs indicates that the dormant state canbe selectively reconstructed. This selectivity also supports thepresence of a locally defined interaction environment at thedeprotected pore surface. Thus, coupling hydrogen-bond-basedinteraction design with structural response enables the dormantstate to be selectively re-formed upon exposure to specificmolecular inputs.15213773, 2026, 40, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/anie.1547062 by National Institute For, Wiley Online Library on [09/10/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OAarticles are governed by the applicable Creative Commons LicenseAngewandte Chemie International Edition, 20265 of 11imageFIGURE 5 Observation of the macroscopic crystal-shape changesaccompanying the two-step SCSC transformation. Bright-field opticalmicroscopy images (top) and optical microscopy images recorded underUV irradiation in the dark (bottom) for Forms I–III.2T.3 Property Changes Accompanying the Phaseransition2.3.1 Changes in Crystal ShapeTcPaIbtclrstzu(titbt(IswotpcTtttttm[he Form I → Form II → Form III SCSC sequence was alsolearly accompanied by macroscopic changes in crystal shape.olarized optical microscopy showed that Form I appeared asflat and homogeneous plate-like single crystal, whereas FormI exhibited shortening along the long-axis direction, followedy further contraction along the long axis and expansion alonghe short axis in Form III (Figure 5, Table S1). These changesan be understood as macroscopic manifestations of anisotropicattice deformation occurring at each stage. In particular, theeduction in the long-axis dimension observed in the first SCSCtep (Form I → Form II) was consistent with the shortening ofhe crystallographic c axis and is attributable to the reorgani-ation of the CAHB network from a 1D ladder to a 2D sheetpon the release of the DMSO molecules bonded to tBuAH+Figure 5). In the second SCSC step (Form II → Form III),he removal of the DMSO molecules protecting the OH groupsnduced a more extensive framework reorganization, includinghe rotation and displacement of sulfonate groups (as observedy single-crystal x-ray diffraction), accompanied by further con-raction along the long axis and elongation along the short axisFigure 5).mportantly, despite these pronounced changes in macro-copic crystal shape, no crystal fracture or significant collapseas observed, and single crystallinity was retained through-ut the transformation (Figure 5). Thus, in the present sys-em, molecular-level rearrangement, changes in the unit-cellarameters, and macroscopic crystal-shape changes proceededontinuously via single-crystal-to-single-crystal transformations.he observed shape change, therefore, reflects not simplehermal deformation or crystal deterioration, but a visuallyraceable manifestation of hydrogen-bond network reorganiza-ion propagating throughout the crystal lattice. In this sense,he present system provides an SCSC platform in whichhe relationship between microscopic structural change andacroscopic crystal morphology can be directly monitored51].imageFIGURE 6 Optical changes accompanying the two-step SCSCtransformation. (a) Photographic images of crystals of Forms I–III. (b)Solid-state UV–vis diffuse reflectance spectra of Forms I–III, shown asKubelka–Munk-transformed data, F(R).2.3.2 Optical Changes Induced by the Phase TransitionEach activation stage in the SCSC sequence was also clearlydistinguished by changes in crystal color. Form I was deep red,Form II was light brown, and Form III was significantly paler,appearing almost white in color (Figure 6a). As a result, thesethree states could be easily distinguished by the naked eye.Accordingly, the solid-state ultraviolet–visible (UV–vis) diffusereflectance spectra showed a stepwise decrease in absorption inthe visible region from Form I to Form II and then to Form III,with particularly marked suppression being observed for the long-wavelength absorption tail (Figure 6b). Additionally, differencesamong the three states were observed in the solid-state excitationspectra, emission spectra, average fluorescence lifetimes, andexternal quantum yields (Figures S13–S17, Table S3), indicatingthat the optical response changed systematically upon activation[52, 53]. These results reveal that each activation stage corre-sponds not to a local perturbation but to a discrete bulk-statechange based on SCSC transformation while retaining singlecrystallinity. Accordingly, the different states can be distinguishednot only structurally but also through their optical responses [54],which are readily distinguishable by visual inspection.2.4 Gas Adsorption Properties2.4.1 Emergence of Preferential NH3 AdsorptionThrough the Present StrategyThe key adsorption result of the present system is the emergenceof NH3-responsive pore-surface function upon transformationfrom the dormant state (Form II) to the active state (Form III). TheNH3 adsorption isotherm of Form III at 298 K rose steeply fromthe low-pressure region, reaching 12.7 mL (STP) g−1 at 0.0105 kPaand 22.2 mL (STP) g−1 at 0.1286 kPa. In contrast, the extent of CO215213773, 2026, 40, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/anie.1547062 by National Institute For, Wiley Online Library on [09/10/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OAarticles are governed by the applicable Creative Commons License6of 11Angewandte Chemie International Edition, 2026imageFIGURE 7 NH3-responsive adsorption properties of the POS. (a) Gas adsorption isotherms of the active state (Form III) for NH3, CO2, O2, H2, andN2 at 298 K. (b) Gas adsorption isotherms of the dormant state (Form II) for NH3, CO2, O2, H2, and N2 at 298 K. (c) Comparison of Forms II and III withrepresentative porous materials in terms of NH3 uptake and the NH3/CO2 uptake ratio at 298 K and ∼1 bar [40–42, 55, 56]. (d) NH3 adsorption–desorptioncycling performance of Form III. (e) PXRD patterns of Form III immediately following preparation, after the NH3 adsorption–desorption measurements,and after exposure to NH3 vapor without desorption, together with the simulated pattern. (f) Diffuse reflectance spectra of Form III before and afterexposure to aqueous NH3 vapor, shown as Kubelka–Munk-transformed data, F(R), together with photographic images of the sample before and afterexposure.aaeoorNSatgtpdssapTmQagwitwdsorption in the same low-pressure region was extremely small,nd minimal adsorption of N2, H2, and O2 was observed over thentire pressure range (Figure 7a). Even near 1 bar, the NH3 uptakef Form III reached 89.2 mL (STP) g−1, whereas that of CO2 wasnly 2.99 mL (STP) g−1, corresponding to an NH3/CO2 uptakeatio of ∼29.8 (Table S4), revealing the pronounced preference forH3 over CO2.uch adsorption behavior cannot be explained by pore formationlone. Rather, it is crucial that, through the two-step structuralransformation accompanied by DMSO removal, phenolic OHroups capable of strong interactions with NH3 are positionedo function as adsorption sites. The present supramolecularrotection–deprotection strategy therefore enables the intro-uction of phenolic OH groups—which are difficult to installelectively yet can strongly interact with NH3—onto the poreurface through controlled structural transformation, yieldingfunctional material that shows a pronounced adsorptionreference for NH3.emperature-dependent NH3 adsorption isotherms were furthereasured to estimate the apparent isosteric heat of adsorption,st (Figure S19). In the reliable uptake region, correspondingpproximately to 0.4–0.7 OH-equivalent, the apparent Qst valuesradually decreased from approximately 60 to 40–45 kJ mol−1ith increasing NH3 uptake. The magnitude of these Qst valuess consistent with appreciable hydrogen-bonding-assisted interac-ions between NH3 and the pore surface of Form III, rather thaneak nonspecific physisorption alone [36].The interaction between the deprotected phenolic OH groupsand NH3 was also supported by IR spectroscopy. After NH3vapor exposure, the broad absorption in the 3500–3000 cm−1region, assigned mainly to phenolic O–H stretching with possiblecontribution from N-H stretching, became more pronouncedand broadened (Figure S21). An increase in the absorptionaround 1460 cm−1, attributable to N–H bending vibrations ofadsorbed NH3/NH3-derived species, was also observed. Simi-lar but weaker spectral changes were detected after the NH3adsorption-desorption measurement, consistent with residualNH3 retained after desorption and with the hysteretic NH3adsorption behavior.2.4.2 Theoretical Analysis of NH3 Adsorption Sites inForm IIITo further clarify the NH3 adsorption sites in Form III, quantumchemical calculations were performed using a cluster modelbased on the experimentally determined Form III crystal struc-ture. To avoid ambiguity arising from the disorder of the phenolicOH groups in the Form III crystal structure, possible OH-orientation patterns were first evaluated by quantum chemicalcalculations, and the most stable pattern was used as a representa-tive framework structure for the subsequent NH3 adsorption-siteanalysis (Figure S22). Three initial adsorption models were con-structed by placing an NH3 molecule near the possible interactionsites: exposed phenolic OH groups, SO3− moieties, and tBuAH+cations (Figure S23). After geometry optimization, the NH315213773, 2026, 40, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/anie.1547062 by National Institute For, Wiley Online Library on [09/10/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OAarticles are governed by the applicable Creative Commons LicenseAngewandte Chemie International Edition, 20267 of 11mbpgshaNlrni(psscnmwolecule was commonly stabilized through O–H⋅⋅⋅N hydrogen-onding interactions with the exposed phenolic OH groups. Inarticular, the models initially placing NH3 near the phenolic OHroups and the tBuAH+ cations converged to similar optimizedtructures, in which the dominant interaction was the O–H⋅⋅⋅Nydrogen bond with the exposed phenolic OH group rather thandirect interaction with the ammonium cation. The model withH3 initially placed near the SO3− moiety also showed stabi-ization involving an O–H⋅⋅⋅N hydrogen-bonding interaction. Theelative electronic energies, electrostatic potential analysis, andoncovalent interaction plots further supported the favorablenteraction environment around the exposed phenolic OH groupsFigure S24 and Table S7). These results indicate that the exposedhenolic OH groups serve as the dominant NH3 adsorptionites in Form III, although secondary contributions from theurrounding framework environment, including the ammoniumations, cannot be completely excluded. Because Form II doesot possess accessible pores suitable for accommodating NH3olecules, a comparable adsorption-site calculation for Form IIas not performed.2F.4.3 Dormant/Active Control of NH3 Adsorptionunction by Protection–DeprotectionTppIigigcTowsaIpsTiedhe dormant/active control of NH3 adsorption function throughrotection–deprotection was clearly demonstrated by the com-arison of the gas adsorption behaviors of Forms II and III.n Form II, no distinct crystallographic voids were observed,ndicating its essentially nonporous nature; the phenolic OHroups also remained protected by DMSO (Figure S6). Accord-ngly, the NH3 uptake of Form II reached only 10.24 mL (STP)−1 near 1 bar, whereas the CO2 uptake was 2.53 mL (STP) g−1,orresponding to an NH3/CO2 uptake ratio of ∼4.05 (Figure 7b,able S4). Additionally, no pronounced adsorption of N2, H2,r O2 was observed, indicating that Form II generally interactseakly with various gases, including NH3. These characteristicsupport the assignment of Form II as a dormant state that isdsorption-inactive prior to functional emergence.n contrast, Form III exhibited a clear NH3 response, and the com-arison between Forms II and III directly illustrates reversiblewitching between the dormant and active adsorption states.hus, in the present system, structural activation simultaneouslynduces deprotection of the OH groups and pore formation,nabling reversible switching between an adsorption-inactiveormant state and an NH3-responsive active state.2.4.4 Reusability and RegenerationTeuaiPrrrhe exposure of phenolic OH groups on the pore surfacenabled reversible NH3 adsorption-desorption and regenerationnder relatively mild conditions [57]. Specifically, in the NH3dsorption-desorption cycling experiments, no marked decreasen uptake was observed even after five cycles (Figure 7d, Table S5).XRD analysis showed that the diffraction pattern of the sampleecovered after the NH3 adsorption-desorption measurementemained consistent with Form III (Figure 7e), indicating thatepeated adsorption and desorption did not cause irreversibleframework collapse or conversion to Form II. Additionally, TGAof the recovered sample showed a weight-loss feature below150◦C that was attributable to desorption of NH3 (Figure S20),suggesting that the adsorbed NH3 can be released under relativelymild conditions.The pronounced hysteresis observed in the NH3 desorptionbranch is mainly attributed to the slow release of NH3 retainedin the phenolic-OH-lined confined pore environment. In thisenvironment, NH3 is stabilized by O-H⋅⋅⋅N hydrogen bonding andadditional weak interactions, as supported by the IR and DFTanalyses. The PXRD pattern after the NH3 adsorption-desorptionmeasurement and the stable uptake over five cycles indicatethat this retention is reversible and does not lead to permanentdegradation of the crystalline framework. This behavior contrastswith adsorption via strong coordination to metal centers andindicates that the present system combines sufficient NH3 affinitywith relatively mild regeneration, demonstrating its potential asa reusable NH3 adsorbent.2.4.5 Visible Response Upon NH3 AdsorptionNH3 adsorption by Form III was also directly observed as avisible response. Upon exposure to vapor from a 35% aqueous NH3solution, the sample changed color within 5 min, accompaniedby a large change in the absorption spectrum (Figure 7f). Thisreveals that Form III can adsorb NH3 not only under high-vacuumgas adsorption conditions but also under milder vapor-exposureconditions. Furthermore, TGA of the exposed sample showedmass changes consistent with the uptake of NH3-containingguest molecules (Figure S20), whereas PXRD indicated that thediffraction pattern after NH3 vapor exposure remained consistentwith Form III (Figure 7e). As a control experiment, Form IIIwas exposed to water vapor under otherwise similar conditions.In contrast to the NH3-vapor-exposed sample, no apparent colorchange was observed after water-vapor exposure. In addition,TGA of the water-vapor-exposed sample showed no appreciableadditional weight-loss feature corresponding to guest uptake(Figure S20). These results indicate that the visible color changeand mass change observed after exposure to vapor from theaqueous NH3 solution are not caused by water vapor alone butare associated with NH3 adsorption.Thus, in contrast to DMSO-induced reprotection, which involvesstructural transformation, NH3 uptake occurred while retainingthe Form III crystalline framework, and this process manifestedas a clear color change. Accordingly, Form III functions as aresponsive adsorbent that captures NH3 while retaining crys-tallinity and visually reports this process through an opticalresponse. Rather than aiming at a maximum uptake capacity, thepresent system is distinguished by the large contrast between NH3and CO2 uptake and by protection–deprotection-based switchingof NH3 adsorption (Figure 7c). Thus, the key feature of this systemis not its uptake capacity alone, but the temporal control over theemergence of NH3-responsive pore-surface functionality.3 ConclusionIn conclusion, this study developed a supramolecular protection–deprotection strategy in a crystalline POS that temporally15213773, 2026, 40, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/anie.1547062 by National Institute For, Wiley Online Library on [09/10/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OAarticles are governed by the applicable Creative Commons License8of 11Angewandte Chemie International Edition, 2026sswfhitrOeeiesNsatadottpeparated framework construction from the emergence of pore-urface functionality. During crystallization, phenolic OH groupsere protected by hydrogen bonding with DMSO, enabling theormation of a crystalline framework based on charge-assistedydrogen bonds. Stepwise removal of DMSO subsequentlynduced a two-step single-crystal-to-single-crystal phase transi-ion, affording a dormant state (Form II), in which the OH groupsemained protected, and an active state (Form III), in which theH groups were exposed on the pore surface together with themergence of porosity. The dormant state was re-formed uponxposure to DMSO or DMA vapor, whereas other solvents did notnduce the same structural response. In contrast, the active statexhibited markedly enhanced NH3 uptake relative to the dormanttate, together with the preferential adsorption of NH3 over CO2,2, H2, and O2 under the present conditions. These findingshow that supramolecular protection–deprotection representskey strategy for the temporal installation of highly interac-ive functional groups within a crystalline porous frameworknd for the reversible switching of the pore surface betweenormant and active states. This strategy may be extendable tother highly interactive functional groups by appropriate selec-ion of supramolecular protecting partners, thereby broadeninghe scope of switchable pore-surface engineering in crystallineorous materials.Author ContributionsKvcrmiwiscazuki Shiga: writing – original draft, formal analysis, investigation,alidation, methodology, software, visualization, conceptualization, datauration. Ryota Yamazaki: investigation, formal analysis, writing –eview and editing, validation, visualization. Hajime Shigemitsu:ethodology, software, investigation, formal analysis, visualization, writ-ng – review and editing. Yuuya Nagata: methodology, formal analysis,riting – review and editing, supervision, software, investigation. Norim-tsu Tohnai: conceptualization, methodology, writing – original draft,upervision, validation, funding acquisition, project administration, datauration.AcknowledgmentsTfdwww2he authors thank Rigaku Corporation, especially Dr. Hiroyasu Sato,or technical assistance with the crystallographic analyses performeduring the revision of this manuscript. The calculations in this studyere performed using the Numerical Materials Simulator at NIMS. Thisork was supported by JST SPRING, Grant Number JPMJSP2138. Thisork was supported by JSPS KAKENHI Grant Numbers 24H00405 and4K21717.Conflicts of InterestThe authors declare no conflicts of interest.Data Availability StatementTShe data that supports the findings of this study are available in theupporting Information of this article.References M31. A. P. Côté, A. I. Benin, N. W. Ockwig, M. O’Keeffe, A. J. Matzger, and O.. Yaghi, “Porous, Crystalline, Covalent Organic Frameworks,” Science10 (2005): 1166–1170. 2. O. M. Yaghi, M. O’Keeffe, N. W. 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See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons LicenseAngewandte Chemie International Edition, 2026 11 of 11https://doi.org/10.1021/acsami.1c24759https://doi.org/10.3390/molecules29112698https://doi.org/10.1021/ja300034jhttps://doi.org/10.1021/acs.est.9b06866 Supramolecular Protection-Deprotection for Switching Pore-Surface Functionality in a Crystalline Porous Organic Salt 1 | Introduction 2 | Results and Discussion 2.1 | Structural Design and Stepwise SCSC Transformation 2.1.1 | Supramolecular Protection of the OH Groups by DMSO 2.1.2 | First SCSC Step: Selective Removal of DMSO Hydrogen-Bonded to the tBuAH+ Cations 2.1.3 | Second SCSC Step: Removal of the OH-Protecting DMSO Molecules 2.2 | Reverse Phase Transition Induced by Vapor Exposure and Supramolecular Reprotection 2.2.1 | Reprotection of the OH Groups by DMSO Vapor 2.2.2 | Selectivity of the Reprotecting Molecules 2.3 | Property Changes Accompanying the Phase Transition 2.3.1 | Changes in Crystal Shape 2.3.2 | Optical Changes Induced by the Phase Transition 2.4 | Gas Adsorption Properties 2.4.1 | Emergence of Preferential NH3 Adsorption Through the Present Strategy 2.4.2 | Theoretical Analysis of NH3 Adsorption Sites in Form III 2.4.3 | Dormant/Active Control of NH3 Adsorption Function by Protection-Deprotection 2.4.4 | Reusability and Regeneration 2.4.5 | Visible Response Upon NH3 Adsorption 3 | Conclusion Author Contributions Acknowledgments Conflicts of Interest Data Availability Statement References Supporting Information