Distribution Control-Oriented Intercalation of a Cationic Metal Complex

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Distribution control-oriented intercalation of a cationic metal complex into layered silicates modified with organosulfonic-acid moieties Minoru SOHMIYA, Takanori Nakamura, Yoshiyuki Sugahara, and Makoto Ogawa Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.8b00547 • Publication Date (Web): 27 Mar 2018 Downloaded from http://pubs.acs.org on March 28, 2018

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Langmuir

Distribution control-oriented intercalation of a cationic metal complex into layered silicates modified with organosulfonic-acid moieties

Minoru Sohmiya1*, Takanori Nakamura2, Yoshiyuki Sugahara3, 4, and Makoto Ogawa1,2 1

Department of Earth Sciences, Waseda University, Nishiwaseda 1-6-1, Shinjuku-ku, Tokyo

169-8050, Japan 2

Graduate School of Creative Science and Engineering, Waseda University, Nishiwaseda 1-6-1,

Shinjuku-ku, Tokyo 169-8050, Japan 3

School of Advanced Science and Engineering, Waseda University, Nishiwaseda 1-6-1,

Shinjuku-ku, Tokyo 169-8050, Japan 4

Kagami Memorial Laboratory for Materials Science and Technology, Waseda University,

2-8-26 Nishiwaseda, Shinjuku-ku, Tokyo 169-0051, Japan

* Corresponding Author. Tel.: +81 3 5286 9864; fax: +81 2 3207 4950. E-mail: [email protected]

Abstract A layered

sodium silicate, octosilicate (Na2Si8O17·nH2O), was modified

with an

organosulfonic-acid moiety (sulfonated propyl (SPr-) group, sulfonated phenethyl (SPhE-) group, or sulfonated p-trifluoromethylphenyl (STFPh-) group) for use as a host material to accommodate a cationic guest, tris(2,2'-bipyridine)ruthenium(II) cation ([Ru(bpy)3]2+). The organosulfonic-acid moiety was bound to the silicate layer via a reaction of an alkylammonium-exchanged octosilicate with a silane coupling agent, and subsequent treatment (oxidation or sulfonation) of the bound organosilyl groups; the surface densities of the organosulfonic-acid moiety were varied by controlling the added amount of silane coupling agents, Adsorption of [Ru(bpy)3]2+ onto surface-modified octosilicates was conducted to find that some surface-modified octosilicates successfully adsorbed [Ru(bpy)3]2+ in the interlayer space (intercalation), while other surface-modified octosiliates did not. In addition, the UV-Vis absorption and the luminescence indicate that intercalated [Ru(bpy)3]2+ diffused in the interlayer and that the distribution of the time-averaged location varied depending on the kind and amount of the organosulfonic-acid moieties. Thus, the kind and surface density of the organosulfonic-acid moiety, which correlates to the interactions between the group and the guest species, the volume of free nanospace for adsorption and motion of guests, and the swelling properties, are the key factors not only for the intercalation ability but also for the dynamics of the guest in the interlayer space.

1 ACS Paragon Plus Environment

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Keywords Layered alkali silicate; Octosilicate; Photoluminescence; Surface modification; [Ru(bpy)3]2+; Intercalation; Host-guest hybrid; Nanoreactor; Confinement effect.

Introduction Construction of hybrid materials based on molecules/ions (guests) and solid materials which provide nanospaces (hosts) has so far been investigated because confinement in the nanospace often changes the guests’ physicochemical characteristics compared to those in homogeneous systems: enthalpy, entropy, and molecular/ionic motion in the nanospace.1-6 These characteristics vary depending on the shape and size of the nanospace and its interactions with the surface. Due to their structural variety, structural regularity, and surface functionality, therefore, inorganic porous materials such as zeolites and mesoporous materials have been employed as host materials.7-10 In addition, layered materials have been utilized to confine molecules/ions in the interlayer space (intercalation), accompanying the expansion/shrinkage of the interlayer space.10-12 An appropriate choice and design of host and guest are required for applications, and the performance should be investigated in terms of guest distributions in the nanospace, the spatial distribution (location, density, and orientation) of guest in the nanospace. The validity of host-guest hybrid materials for controlling the spatial distribution and its associated performance has been shown in some cases; catalysis,9,

13, 14

photocatalysis,15-22

adsorbents11, 23, energy/electron transfer systems,24-27 and ion conductors.28, 29 Designing of host materials via additional modification of their surfaces is effective for improving the properties of the host-guest hybrid materials. One of the promising host materials is crystalline alkali silicates with layered structures (kanemite, makatite, octosilicate (ilerite), magadiite, kenyaite, and others), which possess structural regularity, large interlayer surface areas, and high visible-light transmittance.30 In addition to the confinement behavior of guest species via intercalation, the size, shape, and surface properties of the interlayer nanospace can be tuned by utilizing the interlayer surface functionality: interlayer surface hydroxyl groups can be modified by grafting of organic functional groups. Various organic functional groups have been bound via reactions of alkylammonium-intercalated compounds (reaction intermediates) with silane coupling agents.31-36 The surface density can be varied, moreover, by simply changing the amount of silane coupling agents added.9, 35, 36 This design diversity of the interlayer surface makes it possible to vary not only intercalation characteristics, such as swelling35 and selective adsorption32, but also the physicochemical characteristics (molecular/ionic motion and spatial distribution) of the adsorbates (guest species) in the interlayer space. For the development of applications as well as fundamental science, investigation of


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Langmuir

the guests’ characteristics is, of course, still a topic of interest. In addition to direct observations, such as single molecular detection for luminescent guest molecules/ions37 and simulations,38 the guests’ properties such as photoluminescence are informative concerning the motion and spatial distribution of luminescent guest species, when the host possesses high visible-light transmittance. Due to the photoluminescence reflecting the surroundings, visible light-induced redox potential, and chemical stability, tris(2,2’-bipyridine)ruthenium cation (abbreviated as [Ru(bpy)3]2+)39 has been combined with various host materials. The incorporation of the complex into the frameworks of mesoporous material22, 40 or metal organic frameworks41, 42 (MOF) has been reported to show the controlled spatial distribution. When

[Ru(bpy)3]2+ was

densely packed in the interlayer by co-intercalation with alkyl ammonium ions into magadiite43 or zirconium phosphates,44, 45 or with water soluble polymers into smectites,46 the diffusion, segregation, and aggregation of the Ru(bpy)3]2+ were inhibited. Surface-modification of zirconium phosphates47, 48 or mesoporous silicas24, 26, 49 with an acidic group, on the other hand, enabled diffusion with uniform (homogeneous) distribution in the nanospace. The size and shape of the nanospaces, the interactions between the guest and the adsorption site, the electrostatic repulsion between the cationic guest species, and the co-existence of molecules such as adsorbed water control the motion and spatial distribution of [Ru(bpy)3]2+ in the nanospaces, which should strongly affect the sequential reactions, including photochemical reactions. The main purpose of this study is to assess the manner in which the kind and surface density of the adsorptive sites of the host layered materials affect the intercalation properties and the physicochemical characteristics, including the motion and spatial distribution, of the guest species in the interlayer space. A layered silicate, octosilicate (Na2Si8O17·nH2O), was modified with a sulfonated propyl (SPr-) group, sulfonated phenethyl (SPhE-) group, or sulfonated p-trifluoromethylphenyl (STFPh-) group (organosulfonic-acid moiety), which have different acid strengths, in a controlled amount for use as a host material (Scheme 1), and [Ru(bpy)3]2+ was employed as a guest species. Adsorption of [Ru(bpy)3]2+ onto the surface-modified octosilicate was conducted, and the characteristics of [Ru(bpy)3]2+ in the interlayer space were evaluated by considering both the structural regularity of the surface-modified octosilicates and the photoprocesses of [Ru(bpy)3]2+. Insert Scheme 1.

Experimental Materials. Silica gel (Wakogel® Q-22) was purchased from Wako Pure Chemicals Industries Co. Hexadecyltrimethylammonium chloride (C16TMA Cl) and tris(2-carboxyethyl)phosphine were purchased from Tokyo Chemical Industry Co., Ltd. (3-mercaptopropyl)trimethoxysilane,


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triethoxy[p-(trifluoromethyl)phenyl]silane, and tris(2,2’-bipyridine)ruthenium ([Ru(bpy)3]2+) dichloride

hexahydrate

were

obtained

from

Sigma-Aldrich

Co.

LLC.

Phenethyl(dichloro)methylsilane was obtained from Azumax Co. Sodium hydroxide (NaOH), magnesium oxide (MgO), 35-37 wt% HCl, 60-61 wt% HNO3, methanol, ethanol, toluene, chloroform, and chlorosulfonic acid were obtained from Kanto Chemical Co., Inc. Toluene and chloroform were distilled before use, and the other chemicals were used without further purification. Sample preparation Preparation of ocotosilicate and the hexadecyltrimethylammonium-exchanged form of octosilicate (C16TMA-octosilicate). Sodium octosilicate (Na2Si8O17·nH2O) was synthesized based on the reported methods.50, 51 Silica gel, NaOH and distilled water were mixed in a molar ratio of SiO2 : NaOH : H2O = 4 : 1 : 25.8. The mixture was sealed in a Teflon-lined autoclave and treated hydrothermally at 100 oC for 9 days. The product was separated by centrifugation (3,500 rpm, 10 min), washed with a diluted aqueous solution of NaOH (pH = 10.0), and dried at 40 oC for 2 days. The hexadecyltrimethylammonium-exchanged form of octosilicate (designated as C16TMA-octosilicate) was prepared as follows. Octosilicate powder (2.4 g) was dispersed in 480 mL of a 0.1 mol L−1 C16TMA Cl aqueous solution, and the mixture was allowed to react at room temperature for 1 week. After ion exchange, the solid product was separated by centrifugation (3,500 rpm, 10 min) and washed with methanol. Finally, the powder was dried at 40 °C. Preparation of octosilicate modified with a sulfonated propyl group (SPr-octosilicate). The silylation of octosilicate with (3-mercaptopropyl)trimethoxysilane was conducted in a manner similar to that developed for the silylation of octosilicate.35 One gram of C16TMA-octosilicate

was

dispersed

in

a

distilled

toluene

solution

(50

mL)

of

(3-mercaptopropyl)trimethoxysilane (0.50, 0.33, and 0.18 mL equivalent to 2.0, 1.3, and 0.72 groups per Si8O17, respectively), and the mixture was concentrated for 2 h at 50 hPa and 60 oC to evaporate the volatiles. Before evaporation, the dispersion was heated for 3 days at 60 oC. The product was washed with a mixture of 0.1 mol L-1-HCl and ethanol (1:1 in volume). Reduction

of

the

disulfide

(usually

contained

at

low

level

in

(3-mercaptopropyl)trimethoxysilane) in the silylated octosilicates to thiol was conducted by adding the silylated octosilicate to an ethanol-deionized water (5 : 3 in volume, 40 mL) solution of tris(2-carboxyethyl)phosphine (molar ratio of tris(2-carboxyethyl)phosphine to Si8O17 = 1) and stirring the dispersion for 3 days at 50 oC. The reduced product was separated by centrifugation (3,500 rpm, 20 min), washed with 0.1 mol L-1-HCl and ethanol (1:1 in volume), dispersed in 14 mol L-1 HNO3, and then stirred for 6 h at room temperature. The product was filtered by suction using a PTFE membrane filter with a pore diameter of 0.1 µm (Advantec Co.,


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Langmuir

Ltd.), washed with water, and dried at 60 oC. The oxidized product was designated as SPr(x)-octosilicate, where x denotes the number of bound SPr-groups (per Si8O17) determined from the thermal gravimetric curves. Preparation of octosilicate modified with a sulfonated phenethylmethyl group (SPhE-octosilicate). Sulfonated phenethylmethyl groups were bound onto octosilicate using a modified version of the reported methods.36 One gram of C16TMA-octosilicate was heated at 120 oC for 2 h under a vacuum and then dispersed in a distilled toluene solution (50 mL) of phenethyl(dichloro)methylsilane (0.53, 0.35, and 0.19 mL equivalent to 2.0, 1.3, and 0.72 groups per Si8O17, respectively). The dispersion was heated for 3 days at 60 oC, and then concentrated for 2 h at 50 hPa and 60 oC to evaporate the volatiles. The product was washed with a mixture of 0.1 mol L-1-HCl and ethanol (1 : 1 in volume). The sulfonation of the silylated octosilicates was conducted based on the procedure for sulfonation of a phenethyl group immobilized on mesoporous silica, as follows.24, 52 The silylated octosilicate was dried under reduced pressure at 110 °C for 3 h, dispersed in distilled chloroform with the slow addition of chlorosulfonic acid under a nitrogen flow, and refluxed for 20 h at 60 °C. The weight ratio of silylated octosilicate : chloroform : chlorosulfonic acid was 1 : 150 : 26.2. The products were washed with chloroform, acetone, and deionized water, and dried at 100 °C for 1 day. The products were designated as SPhE(x)-octosilicate, where x denotes the number of the bound SPhE-group (per Si8O17) determined from the thermal gravimetric curves. Preparation of octosilicate modified with a sulfonated p-(trifluoromethyl)phenyl group (STFPh-octosilicate). Sulfonated p-(trifluoromethyl)phenyl groups were bound by the same procedure as that used for SPhE-octosilicates using triethoxy[p-(trifluoromethyl)phenyl]silane instead of phenethyl(dichloro)methyl silane. The amount of the silane coupling agent added to C16TMA-octosilicate toluene dispersion was 0.76 mL equivalent to 2.0 groups per Si8O17. This silylation process was conducted twice to graft a larger amount of the p-(trifluoromethyl)phenyl group. The sulfonation was also conducted by the same procedure as that used for SPhE-octosilicates. The sulfonated product was designated as STFPh(x)-octosilicate, where x denotes the number of the bound STFPh-groups (per Si8O17) determined from the thermal gravimetric curves. Adsorption of [Ru(bpy)3]2+ onto surface-modified octosilicates.

Adsorption of

2+

tris(2,2'-bipyridine)ruthenium(II) complex ([Ru(bpy)3] ) onto surface-modified octosilicates (SPr-, SPhE-, or STFPh-octosilicates) was conducted by reaction between the surface-modified octosilicate (30 mg) and ethanol solutions (20 mL) of [Ru(bpy)3]2+ dichloride hexahydrate (2.5 µ- 0.5 mmol L-1) at room temperature for 1 day. The products were subsequently washed with ethanol and dried under a vacuum at room temperature.


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Characterization.

Page 6 of 37

XRD patterns of the solid products were recorded on a Rigaku RAD IB

powder diffractometer equipped with CuKα radiation operated at 20 mA and 40 kV, except for those of [Ru(bpy)3]2+ adsorbed SPr(1.6)-octosilicate, which was recorded on a Rigaku SmartLab powder diffractometer equipped with D/teX Ultra semiconductor detector and CuKα radiation operated at 30 mA and 40 kV for obtaining clear diffraction patterns. Thermogravimetric and differential thermal analysis (TG-DTA) curves were recorded on a Rigaku TG8120 instrument at a heating rate of 10 oC min-1 under air using α-Al2O3 as the standard material. The ion-exchange capacities of the products were estimated by titration with aqueous sodium hydroxide in the aqueous suspensions. The surface-modified octosilicate (50 mg) was mixed with an aqueous NaCl solution (1.0 mol L-1, 10 mL), and the mixture was stirred for 1 day. Solids were removed by filtration (employing suction) and washed with water, and the filtrate was titrated with 0.01 mol L-1 NaOH. Scanning electron micrographs (SEM) of the Au-coated samples were obtained on a Hitachi S-2380N scanning electron microscope. The coating thickness was 20 nm. The nitrogen adsorption/desorption isotherms were measured at 77 K on a BELSORP-max instrument (Microtrac BEL Corp.). Prior to the measurement, the samples were heated at 120 °C for 3 h under reduced pressure. The amount of [Ru(bpy)3]2+ adsorbed was determined by the change in the [Ru(bpy)3]2+ concentration of the ethanol solution before and after reaction with the surface-modified octosilicates (by the change in the absorbance at 452 nm, measured with a Shimadzu UV-3100PC spectrophotometer). Diffuse reflectance UV-Vis spectra were recorded on a JASCO V-750 spectrophotometer equipped with an integrated sphere unit PIV-756 and a condenser lens unit G265 (see SI 1), using MgO as the standard material. Steady-state photoluminescence spectra were recorded on a Hitachi F-4500 fluorescence spectrophotometer in the wavelength range of 480-800 nm with excitation at 450 nm. The bandwidth of the excitation wavelength was 5 nm. Luminescence spectra in the temperature range of -196 to 120 o

C were recorded on the same fluorescence spectrometer equipped with a cryostat DN-1704

(Oxford Instruments Co. Ltd.). The air inside the cryostat chamber was displaced by nitrogen before cooling measurement. Unless specified or included elsewhere, all spectra were recorded in air at room temperature. Results and discussion Formation of octosilicates modified with an organosulfonic-acid moiety.

Figure 1 shows

the XRD patterns of SPr(x)-, SPhE(x)-, and STFPh(x)-octosilicates, where x denotes the number of the bound organosulfonic-acid moieties (per Si8O17), together with those of sodium octosilicate and C16TMA-octosilicate. All the products showed single diffraction lines ascribable to basal spacings (001). The basal spacing of C16TMA-octosilicate (2.8 nm, Fig. 1b) decreased upon reaction with silane coupling agents, and the values varied depending on their


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Langmuir

bound amounts and the structures of the silane coupling agents. These results indicate that modification with silane coupling agents in the interlayer space of octosilicates was completed without segregation and that C16TMA was concurrently deintercalated. XRD profiles in the range of ca. 20 - 35o indicate that the layer stacking of the C16TMA-octosilicate and surface-modified octosilicates became disordered upon surface modification, and the stacking disorders possibly caused the decrease in the diffraction intensities. The amounts of the bound organosulfonic-acid moieties (SPr-, SPhE-, or STFPh-group) estimated from the thermal gravimetric curves and the ion-exchange capacity determined by titration are listed in Table 1. It seems that the bound amount of organosulfonic-acid moiety is limited depending on the type of group and possibly on the procedure. The bound amounts of organosulfonic-acid moiety determined by the two different methods are consistent, showing that a bound organosulfonic-acid moiety (SPr-, SPhE-, or STFPh-group) works as a single acidic site. Thus, the sulfonation of a part of the phenethyl group or p-(trifluoromethyl) phenyl group was achieved while the other part of the group was eliminated from the surface during sulfonation (Table S1), since chlorosulfuric acid is a strong acid with oxidizing ability, as reported in the previous reports.24, 36, 52 The organosulfonic-acid moieties were consequently bound to the interlayer surface without segregation. The basal spacing increased, in addition, as a function of the bound amount of SPr-group or SPhE-group. The relationships between the basal spacings and the bound amounts show linear regressions as shown in Figure S1. These results mean that the bond angle of the SPr-group or SPhE-group depends on the density of the silanol groups bonded to the SPr-group or SPhE-group, and further suggest that the bound moieties distribute uniformly in the interlayers. Similar relationships have been reported for SPr-octosilicate35 and SPhE-octosilicate36, and the surface modified magadiite.32 Binding of controlled amounts of organosulfonic-acid moiety is a means of obtaining layered solids with controlled layer-charge densities, which is of great importance for determining the physicochemical properties of layered materials.12,

35, 53

The layer-charge densities calculated from the amounts of bound

organosulfonic-acid moieties are from 0.5 to 1.5 group nm-2 (Table 1). Insert Fig. 1 and Table 1

Adsorption of [Ru(bpy)3]2+ onto surface-modified octosilicates. Adsorption of [Ru(bpy)3]2+ onto SPr(1.1)-, SPr(0.9)-, and STFPh(0.5)-octosilicates was examined to find that a negligible amount of [Ru(bpy)3]2+ was adsorbed. [Ru(bpy)3]2+ was adsorbed, on the other hand, onto the other surface-modified octosilicates, SPr(1.6)-, SPhE(0.9)-, and SPhE(0.7)-octosilicates, probably by ion-exchange reactions. Sharp rises at low equilibrium concentration in the adsorption isotherms indicate the strong interactions between the surface-modified octosilicates


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and [Ru(bpy)3]2+ (Figure 2), probably as electrostatic interactions between -SO3- groups originating from the organosulfonic-acid moiety and [Ru(bpy)3]2+. The adsorption isotherms of SPhE-octosilicates can be fitted to the Langmuir adsorption equation, which suggest that the adsorption sites of SPhE-octosiliate for [Ru(bpy)3]2+ can be regarded to be equivalent. Those of SPr(1.6)-ocotosilicate was not fitted to the Langmuir type, however, possibly due to non-uniformly of the adsorption site for [Ru(bpy)3]2+ and/or the structural changes (the expansion/shrinkage of the interlayer space (Figure 3), the conformation changes of the bound SPr-group, adsorption/desorption of adsorbed water, etc.) accompanied with the adsorption of [Ru(bpy)3]2+. All the XRD patterns of the [Ru(bpy)3]2+ adsorbed surface-modified octosilicates show that the diffraction lines abbreviated to the basal spacing are of the single-phase type (though the diffraction intensities decreased after adsorption possibly due to the disordering of the layer stacking), indicating that segregation did not occur. The basal spacing changed slightly from 1.5 nm to 1.7 nm for SPr(1.6)-octosilicate after adsorption of a 0.10 group of [Ru(bpy)3]2+ (per Si8O17) (Fig. 3), and from 1.6 nm to 1.5 nm and from 1.3 nm to 1.4 nm for SPhE(0.9)- and SPhE(0.7)-octosilicates, respectively (Figures S2&S3), where the diffraction lines were slightly distorted upon adsorption of [Ru(bpy)3]2+. Based on the thickness of the silicate sheet of octosilicate, 0.73 nm,50, 51 the gallery height after the [Ru(bpy)3]2+ adsorption is estimated as 0.7-0.9 nm, suggesting that the cations were directly intercalated with slight distortion (the diameter is estimated as 0.82 nm based on the nearest distance between the Ru centers), while [Ru(bpy)3]2+ is not intercalated into sodium octosilicate nor into sodium magadiite under ambient conditions.43 Similar values for the gallery-height expansion by intercalation of [Ru(bpy)3]2+ were also observed for other intercalated compounds.54-57. The surface area of the external surface (out-surface) is less than one five-hundredth smaller compared with that of the internal surface (surface area inside the interlayer space), indicated by SEM images (Figure S4) and N2 adsorption/desorption isotherm (Figure S5). The morphologies of the surface-modified octosilicates before and after surface modification and adsorption of [Ru(bpy)3]2+ are very similar: the particles measure 5-10 µm wide by 5-10 µm long by 0.5-2 µm thick. On the basis of the basal spacings (1.1-1.5 nm), the ratios of external surface to internal surface are calculated to be 1: 500 to 1: 2000. This is also supported by comparison between BET surface area and the ideal surface area of sodium-octosilicate, estimated to be 3.6 m2 g-1 and 1214 m2 g-1 based on the unit-cell size, respectively. Based on the huge difference in the surface areas between external and internal (interlayer) surfaces, most of the [Ru(bpy)3]2+ adsorbed can be regarded to be present in the interlayer space. [Ru(bpy)3]2+ adsorbed onto external surface are ignorable, in other words, even if all the adsorption sites at external surface might be occupied with [Ru(bpy)3]2+. In the case of SPr-octosilicates, the difference in the amounts of the bound SPr-group resulted in different [Ru(bpy)3]2+ adsorption behavior: [Ru(bpy)3]2+ was intercalated into


Page 8 of 37

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Langmuir

SPr(1.6)-octosilicate but not into SPr(1.1)- or SPr(0.9)-octosilicates. One possible reason is the difference in swelling properties as a function of the bound amount of the SPr-group.35 The adsorption behavior is also affected by the interactions between the bound organosulfonic-acid moiety and [Ru(bpy)3]2+. The electrostatic interactions result from the acid strength of the bound group. The acid strength order is estimated as SPr-group < SPhE-group < STFPh-group, based on pKa values of the analogs of the organosulfonic groups (that of ethansulfonic acid is -1.92, and that of p-toluene sulfonic acid is -2.55 in water), and the strong electron-acceptance property of fluorine must make the acid strength greater in comparison with phenyl sulfonic acid group. The acid strength explains that the intercalation of [Ru(bpy)3]2+ into SPhE(0.9)- and SPhE(0.7)-octosilitcates occurred even at lower bound amounts than those of the SPr-group (0.9 and 1.1 group per Si8O17). However, STFPh(0.5)-octosilicate did not cause intercalation. This is possibly because the swelling properties are insufficient, even though the acid strength is high. The adsorption capacities for [Ru(bpy)3]2+ determined from the adsorption isotherms are

0.22,

0.11,

and

0.10

mmol

(g

of

silica)-1 for

SPr(1.6)-,

SPhE(0.9)-,

and

SPhE(0.7)-octosilicate, respectively, corresponding to 0.11, 0.051, and 0.049 group per Si8O17 (Table 2). The adsorption capacities for [Ru(bpy)3]2+ are only 10-25 % equivalent of the amount of the bound organosulfonic-acid moieties. This is probably because the volume of free nanospace for the adsorption and motion of [Ru(bpy)3]2+ is limited depending on the size and amount of the bound organosulfonic-acid moieties (the excluded interlayer surfaces per organosulfonic-acid moiety at the maximum adsorbed amount of [Ru(bpy)3]2+ are calculated as 0.31, 0.25, and 0.48 nm2 for SPr(1.6)-, SPhE(0.9)-, and SPhE(0.7)-octosilicates, respectively, as listed in the seventh column of Table 3, and the calculation method is also mentioned in the caption). It is consequently indicated that not only the interactions between the -SO3- group of the bound functional groups and [Ru(bpy)3]2+ (host-guest interactions) but also the amount of the bound functional groups, which is correlated to the affinity for the guest molecule (including water: swelling) and to the free nanospace, are key factors for the intercalation properties and adsorption capacity. Insert Figs. 2 & 3 and Tables 2 & 3

Quenching behavior of excited-state [Ru(bpy)3]2+ adsorbed onto surface-modified octosilicates. Based on the premise that [Ru(bpy)3]2+ is adsorbed onto the interlayer surface (but not on the external surface), which has been considered in the previous section, following discussion is proceeded. Diffuse reflectance UV-Vis spectra show that an absorption band ascribable to the metal-to-ligand charge transfer (MLCT; S0→S1 transition) band of [Ru(bpy)3]2+ was observed at


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around 450 nm (Figures S6-S8, see SI 1).39 The absorption maxima of the MLCT bands are at 450 nm, 450 nm, and 452 nm for SPr(1.6)-, SPhE(0.7)-, and SPhE(0.9)-octosilicates, respectively, irrespective of the examined adsorbed amount of [Ru(bpy)3]2+. The Kubelka-Munk function plots with respect to the adsorbed amount at the wavelengths of the maxima show nearly linear relationships, that is, a high degree of adherence to Beer’s Law (shown in the insets of Figures S6-S8). The linearity suggests that [Ru(bpy)3]2+ did not form the ground-state complex between the excited-state and ground-state [Ru(bpy)3]2+ (the formation of a ground-state complex has never been reported to our knowledge). The photoluminescence spectra of the [Ru(bpy)3]2+ adsorbed surface-modified octosilicates show an emission ascribable to the phosphorescence of [Ru(bpy)3]2+ at around 600 nm (T1 →S0 transition). The variations in the photoluminescence spectra of [Ru(bpy)3]2+ adsorbed SPr(1.6)-octosilicate as a function of the amounts of [Ru(bpy)3]2+ adsorbed are shown as representative examples in Figure 4 (those of SPhE(0.7)- and SPhE(0.9)-octosilicates are shown in Figures S9 & S10, respectively). The luminescence maxima are shifted gradually toward a longer wavelength region (from 587 to 600 nm) with increases in the amount of adsorbed [Ru(bpy)3]2+ (the insets of Figures 4, S9, S10, and S11). This red shift is possibly caused by the approach of the cations, which enhance the dipole-dipole interactions to lower the triplet energy level. A similar luminescence red shift has been reported for [Ru(bpy)3]2+ adsorbed onto layered zirconium phosphate sulfophenylphosphonate,47, 46

48

24, 49

mica intercalation compounds, and mesoporous silica and its derivatives.

polymer-swelling .

These are summarized as follows; the excitation energy level (S0→S1 transition) of 2+

[Ru(bpy)3]

adsorbed onto surface-modified octosilicates is independent of the adsorbed

amount but the emission energy level (T1→S0 transition) is not; no segregation was observed. These results and a premise that the self-quenching of [Ru(bpy)3]2+ is caused by Dexter energy transfer (see SI 2) suggest: [Ru(bpy)3]2+ is distributed in each interlayer without segregation at a certain distance from the lowering of the singlet energy level; the photo-excited [Ru(bpy)3]2+ and ground-state [Ru(bpy)3]2+ diffused in the interlayer, approached each other, causing a lowering of the triplet energy level, and collided, resulting in the quenching (self-quenching). Insert Fig. 4 The luminescence intensity analysis also supports a relaxation process of 2+

[Ru(bpy)3]

in the interlayer, as mentioned above. In order to compare the luminescence

self-quenching efficiency as a function of the adsorbed amount of [Ru(bpy)3]2+, the integrated area of emission was normalized by the amount of [Ru(bpy)3]2+ (the integrated area of emission in the range of 520-750 nm was divided by the adsorbed amount) to make quasi Stern-Volmer plots. Stern-Volmer equation is derived from steady-state approximation under continuous illumination (eq. 1), based on the assumptions that the luminescence intensity observed for a


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luminophore is proportional to its concentration in the excited state and that the quenching rate between a luminophore and a quencher is proportional to the concentration of the quencher (these conditions are usually met only in homogeneous systems). = 1 + (eq. 1) where I0 is the luminescence intensity in the absence of a quencher, I is the luminescence intensity in the presence of a quencher, [Q] is the concentration of the quencher, and Ksv is the coefficient of the Stern-Volmer plots. The application of Stern-Volmer analysis to these complicated heterogeneous systems, rather than to homogeneous systems, is considered to be valid assuming that the ionic motion is two-dimensionally isotropic in the interlayer nanospace (see SI 3 & SI 4). The quasi Stern-Volmer plot for the self-quenching of [Ru(bpy)3]2+ adsorbed onto SPhE(0.7)-octosilicate shows a linear relationship (Figure 5). Generally, a linear Stern-Volmer plot is indicative of a single luminescent component (Chapter 8 in ref. 58). Thus, these results and the theoretical premise (see SI 2) indicate that the self-quenching reaction of [Ru(bpy)3]2+ is diffusion-controlled and that the distribution of the time-averaged location is uniform (homogeneous) without aggregation in the interlayer space of SPhE(0.7)-octosilicate; the average center-to-center distance between adjacent [Ru(bpy)3]2+ molecules varies with the loading amount of [Ru(bpy)3]2+ in the range of ca. 2 nm to several tens of nm (Tables 2 & 4). Even at ca. 2 nm as the average center-to-center distance, [Ru(bpy)3]2+ did not aggregate, possibly because of electrostatic repulsion between the divalent cations. The coefficient of the Stern-Volmer plot, KSV, is determined, in addition, as 126 L mol-1 (corresponding to 2.3 nm of the distance travelled during the excited-state’s lifetime, Rt,, which is determined by following equation (eq. 2; see SI 4). = 2 =

(eq. 2) 2

where d is a dimension of space (= 2 for two-dimensional space), D is the diffusion coefficient,

τ0 is the luminescence lifetime of the luminophore in the absence of a quencher, p is the probability that a collision between ground-state and excited-state complexes will result in quenching, R is the sum of the ionic radii, and NA is Avogadro’s number. On the other hand, the quasi Stern-Volmer plots for the self-quenching of 2+

[Ru(bpy)3]

adsorbed onto SPr(1.6)- and SPhE(0.9)-octosilicates show upward curvatures

(Figure 5). The upward curvatures were analyzed by the quenching sphere of action model, combined dynamic and static quenching model, and Perrin’s model (the models are briefly reviewed in SI 6). The plot of [Ru(bpy)3]2+ adsorbed onto SPr(1.6)-octosilicate can be fitted


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only to the quenching sphere of action model (Figure 6), which is described using a modified form of the Stern-Volmer equation and Perrin’s equation (eq. 3). = (1 + )exp ( # /1000) (eq. 3) where KD is the dynamic quenching constant, V is the volume of the sphere within which the probability of quenching is absolute (100%) and NA is the Avogadro’s constant. The dynamic quenching constant, KD, and the quenching sphere radius, Ra, for SPr(1.6)-octosilicate are determined to be 288 L mol-1 (corresponding to 5.2 nm of Rt) and 1.5 nm (calculated from V), respectively. The quenching sphere of action model is established based on the condition that when the excited-state and ground-state [Ru(bpy)3]2+ form the apparent static components but not a ground-state complex, all the closely spaced pairs in a certain adjacent distance (the quenching sphere radius, Ra) are immediately quenched. The value (1.5 nm) obtained from the plots is reasonable, although it is slightly larger than those of the other matrices: 1.3 nm for zeolite Y,59 1.1 nm for polysiloxane,60 and 1.4 nm for Nafion.61 Thus, [Ru(bpy)3]2+ diffused at the random distributed time-averaged location in the interlayer. The plot of [Ru(bpy)3]2+ adsorbed onto SPhE(0.9)-octosilicate can be fitted to the quenching sphere of action model and the combined dynamic and static quenching model (Figure 7). Although the quenching sphere of action model determined the quenching sphere radius to be 3.8 nm, this value is too large to be explained by the comparison with the size of [Ru(bpy)3]2 and the previous reports.59-61 The plot is also fitted to the combined dynamic and static model (eq. 4; see SI 6). = (1 + )(1 + ' ) (eq. 4) where KD is the dynamic quenching constant and KS is the association constant for complex formation. This model is established based on the condition that a portion of [Ru(bpy)3]2+ forms a non-luminescent ground-state complex between the excited-state and ground-state [Ru(bpy)3]2+, and the remainder is involved in dynamic (diffusion-controlled) quenching. This is unlikely, however, because no perturbation of the absorption spectra was observed (Figure S8). Consequently, the three models do not explain the self-quenching behavior of [Ru(bpy)3]2+ adsorbed onto SPhE(0.9)-octosilicate. One of possible explanation is that [Ru(bpy)3]2+ diffused in the interlayer without aggregation at the clumped distribution of the time-averaged location, possibly as a result of the steric constraint by the SPhE-group and/or [Ru(bpy)3]2+ itself. In other words, the motion and distribution can be explained by the combination of random distribution and steric constraint.


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Insert Figs. 5-7 and Table 4 The luminescence self-quenching as a function of temperature also indicates that dynamic quenching is dominant (see SI 7 in more detail).26 The luminescence spectra of [Ru(bpy)3]2+ adsorbed onto SPhE(0.7)- and SPhE(0.9)- octosilicates in the temperature range of -196 to 120 °C under nitrogen are shown in Figures 8 & S12, respectively. The spectra for the cooling and heating processes show little difference, meaning that the states of adsorbed [Ru(bpy)3]2+ depend on the temperature rather than the process (Figures 9 and S13). The normal Stern-Volmer plot’s y-axis value divided by the normalized integrated area at a temperature, (I0/I-1)/I0, is plotted as a function of the concentration of [Ru(bpy)3]2+ in the interlayer (Figure 10). Using this value, (I0/I-1)/I0, which eliminates the temperature dependence on luminescence intensity, is valid for evaluating the temperature dependence on quenching efficiency. The plots for [Ru(bpy)3]2+ adsorbed onto SPhE(0.7)-octosilicate show somewhat downward curvatures below 0 oC and the same curvatures below -50 oC, (possibly caused by the freezing or melting of water co-adsorbed in the interlayer), while they show linear relationships at temperatures of 20 and 70 oC (Figure 10A). The slopes increased at high temperature, indicating higher activity of the [Ru(bpy)3]2+ diffusion with increases in temperature (Chapter 8 in ref. 58). The plots for [Ru(bpy)3]2+ adsorbed onto SPhE(0.9)-octosilicate also show that higher temperatures increased the slopes and their linearity (Figure 10B). This means that dynamic quenching is dominant at above ambient temperature. Insert Figs. 8-10 The observed self-quenching behaviors of [Ru(bpy)3]2+ are explained based on the ionic motion (correlated to the mean square displacement) and the spatial distribution (time-averaged location) of the cations in the interlayer space; [Ru(bpy)3]2+ travelled a few nm during the excited-state’s lifetime, and the time-averaged locations are uniform (homogenous), random, or clumped distributions without aggregation for SPhE(0.7)-, SPr(1.6)-, and SPhE(0.9)-octosilicates, respectively (Table 4). To explain the variations in the ionic motion and distribution, the electrostatic repulsion between the divalent cations, [Ru(bpy)3]2+, and steric constraint caused by the organosulfonic-acid moieties and cations must be considered. The electrostatic repulsion between the divalent cations is generally strong enough to cause a larger separation than their van der Waals radii, at which no electron cloud overlapping (including aggregation) occurs. The [Ru(bpy)3]2+ in the interlayer are allowed to form an apparent static component, however, which causes sphere of action quenching, at a high bound organosulfonic-acid moiety density. (The densities are 1.3, 0.8, and 0.5 group nm-2 for SPr(1.6)-, SPhE(0.9)-, and SPhE(0.7)-octosilicates, respectively; sixth column in Table 1). The high density of anionic groups increases the


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population (but decreases the probability) of cations that prevail over the repulsion to approach each other, that is to say, the high density allows random distribution. This is suggested in the homogeneous solution by the potential equation of Debye and Hückel.62 Depending on the amount of the organosulfonic-acid moiety and [Ru(bpy)3]2+, moreover, the volume of free nanospace for the adsorption and motion of [Ru(bpy)3]2+ is reduced. To evaluate the steric constraint effect, the excluded interlayer surface areas per organosulfonic-acid moiety at the maximum adsorbed amount of [Ru(bpy)3]2+ are estimated to be 0.31, 0.25, and 0.48 nm2 for SPr(1.6)-, SPhE(0.9)-, and SPhE(0.7)-octosilicates, respectively (seventh column in Table 3). The divalent cation, [Ru(bpy)3]2+, requires free nanospace larger than 0.53 nm2 per organosulfonic-acid moiety to be in the interlayer space on the assumption that the cations are distributed uniformly and the diameter is 0.82 nm. The smaller the excluded interlayer surface areas per organosulfonic-acid moiety compared with the value (0.53 nm2), the smaller the free nanospace for the cationic motion, causing noticeable steric constraint: the distribution of the time-averaged location of the cation should be biased (clumped) as suggested in the case of SPhE(0.9)-octosilicate. These explanations are inadequate, requiring at least detailed consideration of the heterogeneity of the ion exchange site in a single interlayer space and its steric constraint as illustrated by an example of a homogeneously charged synthetic fluorohectorite.55, 56

Conclusions. Adsorption of [Ru(bpy)3]2+ onto the surface-modified octosilicates was conducted to find that SPr(1.6)-, SPhE(0.7)-, and SPhE(0.9)-octosilicates successfully intercalated [Ru(bpy)3]2+, while the other modified octosiliates did not. In addition, the UV-Vis absorption and luminescence self-quenching behavior of [Ru(bpy)3]2 suggest that [Ru(bpy)3]2+ travelled a few nm in the interlayer during the excited-state’s lifetime and that the time-averaged locations are uniform (homogenous), random, or clumped distributions without aggregation for SPhE(0.7)-, SPr(1.6)-, and SPhE(0.9)-octosilicates, respectively. Uniform/random distribution is suitable for sequential reaction, including photocatalytic reactions with high performance and/or high selectivity, while clumped distribution is suitable for constructing assemblies such as supramolecules with high energy-transfer efficiency. These results mean that not only the interactions between the bound organosulfonic-acid moiety and [Ru(bpy)3]2+ (host-guest interactions) but also the amount of the bound organosulfonic-acid moiety are key factors for the intercalation properties and the motion and distribution of [Ru(bpy)3]2+ in the interlayer space. In other words, precise design of the surface of layered materials can provide controlled motion and distribution of the guests in the interlayer space by a simple procedure alone.


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Associated content Supporting Information The supporting Information is available free of charge on the ACS Publications website at DOI: Kubelka-Munk function (SI 1), theoretical premises (SI 2-5), brief summary of the quenching models (SI 6), detailed discussion on luminescence of [Ru(bpy)3]2+ adsorbed onto SPhE-octosilicates as a function of temperature (SI 7), Table S1, and Figures S1-13. Author Information Corresponding Author *E-mail: [email protected] / [email protected] Notes The authors declare no competing financial interest. Acknowledgements This work was supported by a Waseda University special research project (No. 2016B-078). References (1) Polarz, S.; Kuschel, A., Chemistry in Confining Reaction Fields with Special Emphasis on Nanoporous Materials. Chem.-Eur. J. 2008, 14, 9816-9829. (2) Shchukin, D. G.; Sviridov, D. V., Photocatalytic Processes in Spatially Confined Micro- And Nanoreactors. J. Photochem. Photobiol. C: Photochem. Rev. 2006, 7, 23-39. (3) Roduner, E., Nanoscopic Materials - Size Dependent Phenomena. RSC Publishing: Cambridge, 2006. (4) Kärger, J.; Ruthven, D. M., Diffusion In Nanoporous Materials: Fundamental Principles, Insights And Challenges. New J. Chem. 2016, 40, 4027-48. (5) Majumder, M.; Chopra, N.; Andrews, R.; Hinds, B. J., Nanoscale Hydrodynamics: Enhanced Flow in Carbon Nanotubes. Nature 2005, 438, 44. (6) Holt, J. K.; Park, H. G.; Wang, Y. M.; Stadermann, M.; Artyukhin, A. B.; Grigoropoulos, C. P.; Noy, A.; Bakajin, O., Fast Mass Transport Through Sub-2-Nanometer Carbon Nanotubes. Science 2006, 312 (5776), 1034-7. (7) Kalyanasundaram, K., Photochemistry in Microheterogeneous Systems. Academic Press, Inc.: London, 1987. (8) Ogawa, M.; Saito, K.; Sohmiya, M., Possible Roles of the Spatial Distribution of Organic Guest Species in Mesoporous Silicas to Control the Properties of the Hybrids. Eur. J. Inorg. Chem. 2015, 2015, 1126-36. (9) Yu, C.; He, J., Synergic Catalytic Effects in Confined Spaces. Chem. Commun. 2012, 48, 4933-40.


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Sulfophenylphosphonate. J. Phys. Chem. 1988, 92, 5777-81. (48) Colon, J. L.; Yang, C. Y.; Clearfield, A.; Martin, C. R., Photophysics and Photochemistry of Tris(2,2'-bipyridyl)ruthenium(II) within the Layered Inorganic Solid Zirconium-Phosphate Sulfophenylphosphonate. J. Phys. Chem. 1990, 94, 874-882.


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(49) Ogawa, M.; Kuroda, K.; Nakamura, T., Surface Modification of Mesoporous Silica to Control the States of Tris(2,2 '-bipyridine)ruthenium(II) Cations. Chem Lett 2002, 632-3. (50) Iler, R. K., Ion Exchange Properties of Crystalline Hydrated Silica. J. Colloid Sci. 1964, 19, 648. (51) Vortmann, S.; Rius, J.; Siegmann, S.; Gies, H., Ab Initio Structure Solution from X-Ray Powder Data at Moderate Resolution: Crystal Structure of a Microporous Layer Silicate. J. Phys. Chem. B 1997, 101, 1292-7. (52) Badley, R. D.; Ford, W. T., Silica-Bound Sulfonic-Acid Catalysts. J. Org. Chem. 1989, 54, 5437-43. (53) Ide, Y.; Ogawa, M., Efficient Way to Attach Organosilyl Groups in the Interlayer Space of Layered Solids. Bull. Chem. Soc. Jpn. 2007, 80, 1624-9. (54) Ghosh, P. K.; Bard, A. J., Photochemistry of Tris(2,2'-bipyridyl)ruthenium(II) in Colloidal Clay Suspensions. J. Phys. Chem. 1984, 88, 5519-26. (55) Breu, J.; Raj, N.; Catlow, C. R. A., Chiral Recognition among Trisdiimine-Metal Complexes, Part 4. Atomistic Computer Modeling of [Ru(bpy)3]2+ and [Ru(phen)3]2+ Intercalated into Low Charged Smectites. J. Chem. Soc. Dalton 1999, 835-45. (56) Breu, J.; Stoll, A.; Lange, K. G.; Probst, T., Two-Dimensional Diffraction from Enantiopure and Racemic Monolayers of [Ru(bpy)3]2+ Intercalated into Synthetic Fluorohectorite. Phys. Chem. Chem. Phys. 2001, 3, 1232-5. (57) Villemure, G., Effect of Negative Surface-Charge Densities of Smectite Clays on the Adsorption-Isotherms of Racemic and Enantiomeric Tris(2,2'-bipyridyl)ruthenium(II) Chloride. Clays Clay Miner. 1990, 38, 623-30. (58) Lakowicz, J. R., Principles of Fluorescence Spectroscopy 3rd Edition. 3rd ed.; Springer Science: New York, 2006. (59) Turbeville, W.; Robins, D. S.; Dutta, P. K., Zeolite-Entrapped Ru(bpy)32+: Intermolecular Structural and Dynamic Effects. J. Phys. Chem. 1992, 96, 5024-9. (60) Nagai, K.; Takamiya, N.; Kaneko, M., Molecular-Distribution of Photoluminescent Ru(bpy)32+ Dispersed in a Polymer Film and Its Distance-Dependent Concentration Quenching. J. Photochem. Photobiol. A: Chem. 1994, 84, 271-7. (61) Lin, R. J.; Onikubo, T.; Nagai, K.; Kaneko, M., Investigation of Ru(bpy)32+/Nafion® Film Coated on Electrodes Studied Using Insitu Spectrocyclic Voltammetry and Photoluminescence. J. Electroanal. Chem. 1993, 348, 189-99. (62) Gurney, R. W., Ionic Processes in Solution. McGRAW-HILL Book Company, Inc: New York, 1953.

Scheme, Table, and figure captions Scheme 1. Schematic diagram of the surface modification of octosilicate; x denotes the number


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of the bound organosulfonic-acid moieties (per Si8O17). Table 1. Characteristics of surface-modified octosilicates Table 2. Characteristics of [Ru(bpy)3]2+ adsorbed surface-modified octosilicates Table 3. Calculated spatial volumes and excluded surface areas of surface-modified octosilicates Table 4. Self-quenching coefficients of [Ru(bpy)3]2+ adsorbed onto surface-modified octosilicates Figure 1. XRD patterns of (a) Na-, (b) C16TMA-, (c) SPr(0.9)-, (d) SPr(1.1)-, (e) SPr(1.6)-, (f) SPhE(0.7)-, (g) SPhE(0.9)-, and (h) STFPh(0.5)-octosilicates Figure 2. Adsorption isotherms of [Ru(bpy)3]2+ onto SPr(1.6)-octosilicate (circle), SPhE(0.7)-octosilicate (cross), and SPhE(0.9)-octosilicate (triangle) Figure 3. XRD patterns of [Ru(bpy)3]2+ adsorbed SPr(1.6)-octosilicates. The adsorbed amounts of [Ru(bpy)3]2+ are (a) 0, (b) 0.0010, (c) 0.0046, (d) 0.022, (e) 0.043, and (f) 0.10 group (Si8O17)-1. Figure 4. Photoluminescence spectra of [Ru(bpy)3]2+ adsorbed SPr(1.6)-octosilicates. The adsorbed amounts of [Ru(bpy)3]2+ are (a) 0.0010, (b) 0.046 , (c) 0.022, (d) 0.043, and (e) 0.10 group (Si8O17)-1; the inset shows the relationships between luminescence intensity(circle)/λ max(cross) and the adsorption amount of [Ru(bpy)3]2+. Figure 5. Quasi Stern-Volmer plots of [Ru(bpy)3]2+ adsorbed SPr(1.6)-octosilicate (circle), SPhE(0.7)-octosilicate (cross), and SPhE(0.9)-octosilicate (triangle); the inset shows the extended figure. Figure 6. Sphere of action model fit to the quenching data of [Ru(bpy)3]2+ adsorbed SPr(1.6)-octosilicates; V is the volume of the sphere of action, and Ra is the quenching sphere radius. Figure 7. (A) Sphere of action model fit and (B) combined dynamic and static model fit to the quenching data of [Ru(bpy)3]2+ adsorbed SPhE(0.9)-octosilicates; V is the volume of the sphere of action, and Ra is the quenching sphere radius. Figure 8. Luminescence spectra of [Ru(bpy)3]2+ adsorbed SPhE(0.7)-octosilicates during heating (-196 to 120 °C); (A) 1.4, (B) 30, and (C) 71 mmol L-1. The excitation wavelength is 450 nm. Figure 9. Integrated area of emission (the integrated area of emission in the range of 520-750 nm divided by the adsorbed amount of [Ru(bpy)3]2+) of [Ru(bpy)3]2+ adsorbed SPhE(0.7)-octosilicates as a function of temperature: (A) 1.4, (B) 30, and (C) 71 mmol L-1, under air (filled circle), cooling process under nitrogen (open circle), and heating process under nitrogen (cross)


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Figure 10. Quasi Stern-Volmer plots of [Ru(bpy)3]2+ adsorbed SPhE(0.7)-octosilicates (A) and SPhE(0.9)-octosilicates (B) in the temperature ranges of -196 to 120 °C; 20 oC under air (filled circle) and 100 to -196 oC under nitrogen


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Scheme 1 SO3H

SH

Octosilicate（Na2Si8O17・nH2O）

HO

Oxidation

HO Si

Si O

O

O

O

Silylation

2 µm

SPr(x)-octosilicate SO3H

Ion exchange

H3 C H H

Sulfonation

Si

O

O

H3C

Si O

O

N+ H O OH

2.8 nm SPhE(x)-octosilicate SiO4 tetrahedron Na+

CF3

CF3

HO

Sulfonation

Si O

O

SO 3H

HO Si O

O

STFPhE(x)-octosilicate


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Table 1. Characteristics of surface-modified octosilicates Amount of organosulfonic-acid moiety a

Ion exchange capacity b

Charge density c

mmol (g of silica)-1

group (Si8O17)-1


group (Si8O17)-1

group nm-2

SPr(1.6)-octosilicate

3.2

1.6

3.1

1.4

1.3


2.3

1.1

2.3

1.1

1.0


1.7

0.9

1.7

0.8

0.7

SPhE(0.9)-octosilicate

1.8

0.9

1.7

0.9

0.8


1.2

0.7

1.1

0.6

0.5

STFPh(0.5)-octosilicate

1.0

0.5

1.0

0.5

a

0.5 o

Determined from thermal gravimetric curves (Ignition loss at temperature range of 400 - 800 C).

b

Determined by titration. c Calculated based on the ideal surface area of octosilicate (= 0.74 × 0.74 × 2 nm2 per unit cell).


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Page 24 of 37

Table 2. Characteristics of [Ru(bpy)3]2+ adsorbed surface-modified octosilicates Average center-to-center distance between

Amount of adsorbed [Ru(bpy)3]2+ mmol (g of silica)-1 SPr(1.6)-octosilicate



a

group (Si8O17)-1

adjacent [Ru(bpy)3]2+ b %a

nm

0.0022

0.0010

0.13

23

0.010

0.0046

0.60

11

0.049

0.022

2.9

4.9

0.093

0.043

5.5

3.5

0.15

0.069

8.9

2.8

0.23

0.10

13

2.3

0.0017

0.00080

0.20

26

0.0089

0.0042

1.0

11

0.046

0.022

5.2

5.0

0.11

0.052

12

3.3

0.0020

0.00090

0.27

24

0.0089

0.0042

1.2

11

0.044

0.021

6.0

5.1

0.10

0.049

14

3.3

Percentage of organosulfonic-acid moiety occupied by [Ru(bpy)3]2+.

surface area of octosilicate and the amount of adsorbed [Ru(bpy)3]2+ ( = 0.74 × 0.74 / amount of adsorbed [Ru(bpy)3 ]2+ (group per Si8O17 ) ).


b

Calculated based on the ideal

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Table 3. Calculated excluded surface areas of surface-modified octosilicates Amount of adsorbed [Ru(bpy)3]2+


SPhE(0.9)-octosilic ate

SPhE(0.7)-octosilic ate

a

Basal spacing

Surface area per organosulfonic-acid moiety b

Excluded interlayer surface area per organosulfonic-acid moiety c


group (Si8O17)-1

%a

nm

nm2 (group)-1

nm2 (group)-1

-

-

-

1.5

0.77

0.17

0.23

0.11

13

1.7

0.77

0.31

-

-

-

1.6

1.3

0.28

0.10

0.049

12

1.5

1.3

0.25

-

-

-

1.4

2.0

0.43

0.11

0.050

14

1.5

2.0

0.48

Percentage of organosulfonic-acid moiety occupied by [Ru(bpy)3]2+. b Calculated based on the ideal

surface area of octosilicate ( = ideal surface area / amount of organosulfonic-acid moiety). c Calculated based on the assumption that the volumes of single SPr-and SPhE-groups equal 0.148 and 0.275 nm3, respectively ( = (Volume of interlayer space – amount of the organosulfonic-acid moiety x volume of SPror SPhE-group) / ((basal spacing – layer thickness) x charge density)).


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Table 4. Self-quenching coefficients of [Ru(bpy)3]2+ adsorbed onto surface-modified octosilicates a Model

KD

KS

Rt

Ra

Distribution of time-averaged

L mol-1

L mol-1

nm

nm

location of [Ru(bpy)3]2+


Quenching sphere of action

288

-

5.2

1.5

Random


Quenching sphere of action

313

-

5.6

3.8

Clumped

Combined dynamic &static model

158

13

2.8

-

-

Normal Stern-Volmer

126

-

2.3

-

Uniform

SPhE(0.7)-octosilicate a

The models and the methods for calculation are briefly described in SI 5.


Page 27 of 37

Figure 1

1.2 nm 1.6 nm 1.3 nm Intensity / (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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1.5 nm

(x5)

(h)

(x5)

(g)

(x5)

(f)

(x5)

(e)

(x2)

(d)

1.3 nm 1.2 nm

(c)

2.8 nm

(b)

1.1 nm 10

(a) 20

2θ (CuKα) /

30

40

o


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Figure 2


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Page 29 of 37

Figure 3

1.7 nm 1.5 nm Intensity / (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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1.5 nm 1.4 nm 1.3 nm 1.3 nm 1.5 nm

(g) (f) (e) (d) (c) (b) (a)

2θ (CuKα) / o


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Figure 4


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Figure 5


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Figure 6


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Figure 7


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Figure 8


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Figure 9


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Figure 10


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Table of Contents

Uniform


Random


Clumped



Distribution Control-Oriented Intercalation of a Cationic Metal Complex

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