J. Phys. Chem. 1993,97, 3819-3823
3819
Novel Controlled Luminescence of Tris(2,2'-bipyridine)ruthenium(II) Intercalated in a Fluortetrasilicic Mica with Poly(vinylpyrrolidone) Makoto Ogawa,' Misako Inagaki,? Nobuhiro Kodama,* Kazuyuki KurOda,**tand Chuzo Katot Department of Applied Chemistry, Waseda University, Ohkubo 3, Shinjuku-ku, Tokyo 169, Japan, and TOSOH Corporation, Hayakawa 2743- 1 , Ayase-shi, Kanagawa 252, Japan Received: November 9, 1992; I n Final Form: January 11, I993
Tris( 2,2'-bipyridine)ruthenium(II) (Ru(bpy)32+)-fluortetrasilicic mica (TSM)-poly(vinylpyrro1idone) (PVP) intercalation compounds were prepared, and the photoluminescent behavior of intercalated Ru(bpy)3*+ was investigated. The luminescence maxima of intercalated Ru(bpy)jZ+ shifted gradually toward the blue with decreased loading of Ru(bpy)j2+, reflecting the change in the polarity and/or rigidity of the microenvironment of R u ( b p y ) P , presumably caused by cointercalated PVP. Moreover, R ~ ( b p y ) 3 ~self-quenching + was suppressed even at its high concentration loading. It was supposed that cointercalated PVP prevented self-aggregation by surrounding Ru(bpy)j2+ in close contact in the sterically limited interlayer spaces.
Introduction Photoprocesses on solid surfaces have attracted increasing attention from a practical viewpoint of uses such as solar energy conversion and preparation of thin films.' Ru(bpy)j2+ is one of the molecules studied most extensively because of its unique combination of chemical stability, luminescence, and so on.2Since the spectroscopic features of R u ( b p y ) ~ ~are + environmentsensitive, photochemical and photophysical investigations are useful for the study of surface p h e n ~ m e n a . In ~ other words, we can modify the attractive propertiesof R ~ ( b p y ) , ~by+introduction into appropriate matrices. Along this line, photochemical and photophysical studies of R ~ ( b p y ) ~on~ +ion-exchange resins," micelles,5cellulose,6porous Vycor glass,' oxides? semiconductors? zeolites,I0clay minerals,' '-z2 and other layered material~2~+2~ have vigorously been investigated. Among possible matrices, layered clay minerals, in particular smectites, provide interesting two-dimensional heterogeneous media for photochemical processes. Smectitesare 2: 1-typelayered clay minerals consisting of negatively charged silicate layers and readily exchangeable interlayer cations and possess various attractive features such as adsorptive property and large surface area.25 Studies on physicochemical properties in such ordered matrices have the advantage that the reaction behavior may be understood in connection with the structure at a molecular level. Moreover, we can control photochemical reaction by organizing reactants onto the two-dimensional clay surfaces. Photoprocesses of R ~ ( b p y ) ~adsorbed ~+ on smectites have already been and two types of quenching of the excited state of R ~ ( b p y ) have ~ ~ +been pointed out. One is self-quenchingdue to aggregation of Ru(bpy)j2+,and the other is quenching by iron, which is included in natural smectites. To overcome the limitation of natural smectites as a support of photoprocess of R u ( b p y ) ~ ~we + , prepared a novel host-guest system, Ru( bpy)32+-swelling mica-poly(vinylpyrro1idone) (PVP) intercalation compounds. To avoid quenching of the excited state of R ~ ( b p y ) , ~by+iron, an artificial swelling mica (fluortetrasilicic mica; abbreviated TSM26-27) was used as the host material. Since not all Na in Na-TSM (NaMg25Si4010F2)was exchangeable, Na-TSM possesses a swelling property similar to those of smectites.2' Cointercalated PVP was expected to alter the microenvironment of R ~ ( b p y ) ~ 2as+ well as to isolate them. +
Waseda University.
1
TOSOH Corp.
Experimental Section Materials. Na-TSM, which was synthesized from S O 2 ,MgO, and Na2SiF6, was kindly supplied from Topy Industries Co. and used after nonexpandable impurities were removed by a dispersion-sedimentation method. The ideal composition of Na-TSM was NaMg2 s S ~ ~ ~and ~ the O cation F ~ exchangecapacity , ~ ~ (CEC) was 97 mequiv/ 100 g of TSM, which was determined by ICP of Ca-TSM. Ca-TSM was prepared by a conventional solution method. Ru(bpy)3Cly6H20 (Aldrich) was used after recrystallization fromdeionized water. PVP (Mw = 1000,Tokyo Kasei Co.) was used as received. Sample Preparation. R~(bpy)~*+-TsMintercalation compounds were prepared by cation exchange of Na-TSM with aqueous solutions of R ~ ( b p y ) 3 ~and + subsequent washing with deionized water. The amount of added Ru(bpy)32+varied from 1 to 100% of the CEC of the TSM. R U ( ~ P ~ ) ~ ~ + - T S M - Pintercalation VP compounds were prepared as follows. A TSM-PVP intercalation compound was prepared according to the method used for the preparation of a montmorillonite-PVP intercalation compound.28 Na-TSM was stirred in an aqueous solution of PVP with a weight ratio of PVP to Na-TSM of 1.5. After repeated washings with methanol, the compound was dried and dispersed in water again. Aqueous solutions of R ~ ( b p y ) , ~were + then added to the suspension, and the mixture was stirred for 1 day and washed with deionized water to remove excess R ~ ( b p y ) ~ ~The + . amount of added Ru(bpy)32+varied from 1 to 100% of the CEC of the TSM. Characterization. X-ray powder diffraction patterns were obtained on a Rigaku RADI-B diffractometer using Mn-filtered Fe Ka radiation. The composition of the products was determined by ICP (Japan Jarrell-Ash ICAP 57511) and elemental analysis (Yanagimoto MT-3). Diffusereflectancespectrawere recordedon a Shimadzu U-210 spectrometer. Steady-state luminescence spectra were recorded on a Shimadzu RF-5000 fluorospectrometer in the range 5 0 0 800 nm with excitation at 475 nm. The bandwidth of theexcitation wavelength and emission wavelength was 1.5 nm. Luminescence decay profiles were obtained by using a HORIBA NAES-700F fluorescence lifetime spectrometer with a flash lamp as a light source. Results Ru(bpy)3*+-TSMIntercalationCompounds. By the reactions between Na-TSM and Ru(bpy)32+, orange products were obtained. The visible spectra of the products showed the absorption
0022-3654/93/2097-3819$04.00/0 0 1993 American Chemical Society
3820
Ogawa et al.
The Journal of Physical Chemistry, Vol. 97, No. 15, 1993 i
TABLE k Amounts of Adsorbed Ru(bpy)32+and Absorption and Luminescence Maxima of the R~(bpy)3~+-TsM Intercalation Compounds amt of Ru(bpy)J2+, mmol/ 100 g: of TSM
absorD max. nm
lumin max. nm
1 2 8 17 33 40
474 474 470 468 468 464
608 608 61 1 61 1 61 1 612
f) 1
500
1
600 700 Wavelength 1 nm
800
Figure 1. Luminescence spectra of R ~ ( b p y ) 3 ~ + - T s Mintercalation compounds with different loadings of R ~ ( b p y ) 3 ~ +(a) : 1, (b) 2, (c) 8, (d) 17, (e) 33, and (f) 40 mmo1/100 g of TSM.
band due to the “metal-to-ligand charge-transfer” transition (MLCT) of R ~ ( b p y ) 3 ~around + 460 nm. (The positions of the absorption maxima are listed in Table I.) The peaks shifted toward the red compared with that (450 nm) observed in an aqueous solution. Figure 1 shows the luminescence spectra of the R~(bpy)3~+TSM intercalationcompounds. The wavelengths of luminescence maxima are listed in Table I. The luminescence maxima were observed around 610 nm, which was close to that of an aqueous solution of R ~ ( b p y ) 3 ~(608 + nm) and consistent with those observed for Ru (bpy) 2+ intercalated in montmorillonite.12 The XRD partterns of the products are shown in Figure 2. When the amounts of R ~ ( b p y ) ~were ~ + 33 or 40 mmo1/100 g of TSM, the basal spacing was 1.80 nm, indicating the expansion of the interlayer space by 0.84 nm. (The basal spacing of dried Na-TSM was 0.96 nm.) Figure 2b shows the XRD pattern of the product at the loading of 40 mmo1/100 g of TSM. The intercalation of tris(bpy) chelate complexes into smectitesrequires the expansion of the interlayer space by ca. 0.8 nm29 and intercalated complexes arranged as a monomolecular coverage with their three-fold axis perpendicular to the silicate sheet. The basal spacings of the R ~ ( b p y ) ~ ~ + - T intercalation sM compounds indicate intercalationof R u ( b p ~ ) 3 and ~ + a monolayerarrangement of intercalated R~(bpy)3~+. Figure 2c shows the XRD pattern of the R~(bpy)3~+-TsM intercalationcompound at the loading of 17 mmol/ 100g of TSM. When the amounts of R ~ ( b p y ) were ~ ~ + 8 and 17 mmo1/100 g of TSM, the d(001) diffraction peaks were split into two (segregation); one shows the basal spacing of ca. 1.8 nm due to Ru( b ~ y ) ~ 2intercalated, + and the other shows that of ca. 1.5 nm due to hydrated Na-TSM. Thus, intercalated R ~ ( b p y ) 3 ~ions + were thought to aggregate within an interlayer space at low loading levels of R ~ ( b p y ) ~ ~At + .loadings of 1 and 2 mmo1/100 g of TSM, the basal spacing did not change, indicating the adsorbed R ~ ( b p y ) 3 ~occupied + the external surface of TSM or the small proportion of the expanded part could not be detected by the conventional XRD measurement. Ru( ~ ~ Y ) ~ ~ + - T S M - Intercalation PVP Compounds. The XRD pattern of the TSM-PVP intercalation compound is shown in
1
2 3
1
1
4
5 6 7 8
1
1
1
1
1
1
91011
20 / deg (Fe K a ) Figure 2. X-ray powder diffraction patterns of (a) Na-TSM, (b, c) Ru(bpy)32+-TSM intercalation compounds a t loadings of 40 and 17 mmol/ 100 g of TSM, (d) TSM-PVP intercalation compound, and (e, f) Ru(bpy)3*+-TSM-PVP intercalation compounds at loadings of 17 and 43 mmo1/100 g of TSM. I
m
y TSM-PVP
TSM
I
J.
Ru(bpy)32+-TSM-PVP
Figure 3. Schematic structure of (a, top left) Na-TSM, (b, bottom left) R ~ ( b p y ) 3 ~ + - T s Mintercalation compound, (c, top right) TSM-PVP intercalation compound, and (d, bottom right) Ru( bpy)32+-TSM-PVP intercalation compound.
Figure 2d. The basal spacing of the TSM-PVP intercalation compound was 2.30 nm, indicating the expansion of the interlayer space by 1.34 nm. Additionally, the infrared spectrum showed characteristic bands due to PVP (C-H stretching, 2965 cm-1; C-H bending, 1425-1465 cm-1) even after repeated washing with methanol. These results confirmed the formation of a TSMPVP intercalation compound. From the molecular thickness of vinylpyrrolidone monomer (0.56 nm),30 intercalated PVP was thought to be arranged as a bimolecular coverage (Figure 3c). By the reaction with R ~ ( b p y ) 3 ~ +orange , products were obtained. The XRD patterns of the R u ( ~ ~ ~ ) ~ ~ + - T S M - P V P intercalation compounds a t loadings of 17 and 43 mmo1/100 g of TSM are shown in parts e and f of Figure 2. The basal spacings of the R U ( ~ P ~ ) ~ ~ + - T S M - Pintercalation VP compounds with different loading levels of R ~ ( b p y ) 3 ~are + listed in Table 11. The expansion of the interlayer space varied from 1.39 to 1.68 nm. (The values were determined by subtracting the thickness of the
Controlled Luminescence of R ~ ( b p y ) , ~ +
The Journal of Physical Chemistry, Vol. 97, No. 15, 1993 3821
TABLE 11: Basal Spacings, Amounts of Adsorbed Species, and Absorption and Luminescence Maxima of the R U ( ~ ~ ~ ) ~ ~ + - T S MIntercalation -PVP Compounds amt of ratio of Ru(bpy),!+, basal amt of PVP, mmo1/100 g spacing, g/IOO g PVP to ofTSM nm ofTSM Ru(bpy)l'+ TSM-PVP
2.30
42
-
1
2.36 2.37 2.35 2.45 2.59 2.64
42 42 42 36 29 24
384" 192" 48" 19" 80 5"
2 8 17 33 43
03
absorp lumin max. nm max,nm 465 464 458 464 464 466
10
. 0
588 592 596 604 605 608
0
0
Molar ratio of PVP monomer unit to Ru(bpy),?+.
0
e ?
10
20
30
40
Lordlng of Ru(bpy)g2+ (mmoV100g TSM)
d
Ps
Figure 5. Intensity of luminescence for the products as a function of the -TSM compounds; loading of Ru(bpy)3?+: (A) R U ( ~ ~ ~ ) ~ ~ +intercalation (0)R U ( ~ P ~ ) ~ ~ + - T S M - Pintercalation VP compounds.
C
TABLE III: Luminescence Lifetimes and Relative Ratios of Fast ( T I ) and Slow ( T Z ) Components Observed for the Ru(bpy)sZ+-TSM and Ru(bpy)3*+-TSM-PVP Intercalation Compounds amt of R ~ ( b p y ) 3 ~ + , mmol/ 100 g of T S M
500
600
700
800
Wavelength I nm
Figure 4. Luminescence spectra of R u ( ~ ~ ~ ) ~ ~ + - T S M intercalation -PVP compounds withdifferent loadingsof Ru(bpy)j2+: (a) I , (b) 2 , (c) 8, (d) 17, (e) 33, and (f) 43 mmo1/100 g of TSM.
silicate layer (0.96 nm) from the observed d(001) values.) The basal spacings obtained here were large enough to accommodate both Ru(bpy)j2+ and PVP (Figure 3d). The amounts of intercalated R ~ ( b p y ) , ~and + PVP are listed in Table 11. A part of intercalated PVP was desorbed through ion exchange. The amounts were determined by subtracting that of bpy, which were estimated on the basis of the amounts of ruthenium, from the total organic contents based on elemental analysis. With the increase in the loading of Ru(bpy),*+, higher amounts of PVP were desorbed. It is supposed that a part of PVP must be desorbed to accommodate bulky R ~ ( b p y ) , ~ + . In the absorption spectra of the products, the MLCT absorption band of Ru(bpy),*+ appeared and the position shifted toward the red (
