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Langmuir 2003, 19, 30-39
Photoinduced Energy Transfer between Ruthenium and Osmium tris-Bipyridine Complexes Covalently Pillared into γ-ZrP Fabrice Odobel,*,† Dominique Massiot,‡ Benjamin S. Harrison,§ and Kirk S. Schanze*,§ Laboratoire de Synthe` se Organique, Faculte´ des Sciences et des Techniques, BP 92208, 44322 Nantes Cedex 03, France, Centre de Recherche sur les Mate´ riaux des Hautes Tempe´ ratures, UPR CNRS 4212, 1D Avenue de la Recherche Scientifique, 45071 Orle´ ans Cedex 02, France, and Department of Chemistry, University of Florida, P.O. Box 117200, Gainesville, Florida 32611 Received June 3, 2002. In Final Form: October 3, 2002 This paper describes the preparation and photophysical characterization of hybrid materials made of a γ-ZrP covalently pillared with two complexes: Ru(bpy)2L and Os(bpy)2L (bpy ) 2,2′-bipyridine and L ) 5,5′-bis(dihydroxyphosphoryl)-2,2′-bipyridine). A high degree of phosphate (H2PO4) exchange by the complexes in the γ-ZrP matrix was achieved (25% intercalation) by preintercalating the γ-ZrP with octylamine. Materials with different Os/Ru ratios were prepared, allowing the study of the efficiency of energy transfer as a function of the Ru/Os ratio (Ru/Os ratios ) 1/0, 1/0.35, 1/0.6, 1/0.8, 1/1, and 0/1). Powder X-ray diffraction shows that the interlayer space of the intercalated γ-ZrP is approximately 18.6 Å in all of the intercalated materials. Solid-state 31P NMR confirms that the complexes are covalently bonded to the zirconium of the γ-ZrP phase. All of the materials exhibit moderately strong metal-to-ligand charge transfer (MLCT) emission from the Ru and/or Os chromophores. In the mixed samples the Ru-based emission is strongly quenched, indicating that in the γ-ZrP matrix rapid Ru to Os energy transfer occurs. On the basis of the lifetimes of the Ru MLCT luminescence, the energy transfer rate is estimated to be 2-3 × 108 s-1 for chromophores that are adjacent in the γ-ZrP matrix.
Introduction The use of the microenvironment of a solid host to promote and control the efficiency of a light-induced process is of current interest in the field of heterogeneous photochemistry.1,2 Many studies have shown that the photophysical properties and photochemical reactions of dyes immobilized in solids are strongly affected by their incorporation into a solid matrix.3 These materials have potential for use in applications that require key functions such as light-harvesting antenna,4,5 long-lived photoinduced charge separation6-8 for use in solar energy conversion and storage, and electro-optical molecular devices. Various media such as silica,9 sol-gel glasses,10 transition * To whom correspondence should be addressed. E-mail addresses:
[email protected]; kschanze@ chem.ufl.edu. † Laboratoire de Synthe ` se Organique, Faculte´ des Sciences et des Techniques BP 92208. ‡ Centre de Recherche sur les Mate ´ riaux des Hautes Tempe´ratures, UPR CNRS 4212. § University of Florida. (1) Ogawa, M.; Kuroda, K. Chem. Rev. 1995, 95, 399-438. (2) Meyer, G. J. Molecular Level Artificial Photosynthetic Materials; John Wiley & Sons: New York, 1997. (3) Ramamurthy, V., Schanze, K. S., Eds. Solid State and Surface Photochemistry; Marcek-Dekker: New York, 2000. (4) (a) Pauchard, M.; Devaux, A.; Calzaferri, G. Chem. Eur. J. 2000, 6, 3456-3470. (b) Kincaid, J. R. Chem. Eur. J. 2000, 6, 4055-4061. (5) Kaschak, D. M.; Mallouk, T. E. J. Am. Chem. Soc. 1996, 118, 4222-4223. (6) Kaschak, D. M.; Lean, J. T.; Waraksa, C. C.; Saupe, G. B.; Usanao, H. U.; Mallouk, T. E. J. Am. Chem. Soc. 1999, 121, 3435-3445. (7) Slama-Schwok, A.; Ottolenghi, M.; Avnir, D. Nature 1992, 355, 240-242. (8) (a) Vermeulen, L. A.; Thompson, M. E. Nature 1992, 358, 656658. (b) Byrd, H.; Suponeva, E. P.; Bocarsly, A. B.; Thompson, M. E. Nature 1996, 380, 610-612. (c) Abdelrazzaq, F. B.; Kwong, R. C.; Thompson, M. E. J. Am. Chem. Soc. 2002, 124, 4796-4803.
metal chalcogenophosphates,11 membranes,12 LangmuirBlodgett films,13-15 and microporous crystalline matrixes such as zeolites,4,16 phosphates,5,6,15,17-22 and phospho(9) Fisher, D. L.; Harper, J.; Sailor, M. J. J. Am. Chem. Soc. 1995, 117, 7846-7847. (10) (a) Mongey, K. F.; Vos, J. G.; Maccraith, B. D.; McDonagh, C. M.; Coates, C.; McGarvey, J. J. J. Mater. Chem. 1997, 7, 1473-1479. (b) Mongey, K. F.; Vos, J. G.; MacCraith, B. D.; McDonagh, C. M. Coord. Chem. Rev. 1999, 185-186, 417-429. (11) (a) Jakubiak, R.; Francis, A. H. J. Phys. Chem. 1996, 100, 362367. (b) Lifshitz, E.; Clement, R.; Yu-Hallada, L. C.; Francis, A. H. J. Phys. Chem. Solids 1991, 52, 1081-1086. (12) (a) Fendler, J. H. Acc. Chem. Res. 1980, 13, 7-13. (b) Iida, K.; Kiriyama, H.; Fukai, A.; Konings, W. N.; Nango, M. Langmuir 2001, 17, 2821-2827. (c) Khairutdinov, R. F.; Hurst, J. K. J. Phys. Chem. B 1998, 102, 6663-6668. (d) Mihara, H.; Tomizaki, K.-y.; Fujimoto, T.; Sakamoto, S.; Aoyagi, H.; Nishino, N. Chem. Lett. 1996, 187-188. (e) Nango, M.; Iida, K.; Matsuura, M.; Yamaguchi, M.; Sato, K.; Tanaka, K.; Akimoto, K.; Yamashita, K.; Tsuda, K.; Kurono, Y. Langmuir 1996, 12, 450-458. (13) (a) Kuhn, H. Pure Appl. Chem. 1981, 53, 2105-2122. (b) Seefeld, K. P.; Moebius, D.; Kuhn, H. Helv. Chim. Acta 1977, 60, 2608-2632. (c) Vuorimaa, E.; Lemmetyinen, H.; Van der Auweraer, M.; De Schryver, F. C. Thin Solid Films 1995, 268, 114-120. (d) Yamazaki, T.; Yamazaki, I.; Osuka, A. J. Phys. Chem. B 1998, 102, 7858-7865. (14) Gust, D.; Moore, T. A.; Moore, A. L.; Luttrull, D. K.; DeGraziano, J. M.; Boldt, N. J.; Van der Auweraer, M.; De Schryver, F. C. Langmuir 1991, 7, 1483-1490. (15) Mallouk, T. E.; Kim, H.-N.; Ollivier, P. J.; Keller, S. W. Compr. Supramol. Chem. 1996, 7, 189-217. (16) (a) Knops-Gerrits, P.-P. H. J. M.; De Schryver, F. C.; van der Auweraer, M.; Van Mingroot, H.; Li, X.-y.; Jacobs, P. A. Chem.sEur. J. 1996, 2, 592-597. (b) Yoon, K. B. Chem. Rev. 1993, 93, 321-339. (17) (a) Kaschak, D. M.; Johnson, S. A.; Waraksa, C. C.; Pogue, J.; Mallouk, T. E. Coord. Chem. Rev. 1999, 185-186, 403-416. (b) Kumar, C. V.; Chaudhari, A.; Rosenthal, G. L. J. Am. Chem. Soc. 1994, 116, 403-404. (18) Colon, J. L.; Yang, C. Y.; Clearfield, A.; Martin, C. R. J. Phys. Chem. 1988, 92, 5777-5781. (19) (a) Colon, J. L.; Yang, C. Y.; Clearfield, A.; Martin, C. R. J. Phys. Chem. 1990, 94, 874-882. (b) Kumar, C. V.; Williams, Z. J. J. Phys. Chem. 1995, 99, 17632-17639.
10.1021/la026029t CCC: $25.00 © 2003 American Chemical Society Published on Web 12/07/2002
Complexes Covalently Pillared into γ-ZrP
nates8,23 have been used to organize photochemically active compounds. Many examples of matrix effects on excited-state properties and photoinduced charge and energy transfer processes have been described in the literature. For example, Thompson and co-workers reported photoinduced charge separation that lasts microseconds to hours in a zirconium viologen bis-phosphonate,8,23 while Dutta,24 Mallouk,25 and Kincaid26 demonstrated that irradiation of ruthenium tris-bipyridine entrapped in zeolite pores in the presence of electron acceptors gives rise to efficient charge separation. More recently, Calzaferri and coworkers developed an elegant artificial antenna for light transport with several dyes intercalated in zeolite nanocrystals.4 Ruthenium and osmium polypyridine metal complexes exhibit versatile photochemical and photophysical properties,27,28 and the spectroscopic properties of Ru(bpy)32+ have been thoroughly investigated in a number of solid media. For example, it has been shown that immobilization of Ru(bpy)32+ in zeolites increases the excited-state lifetime apparently by increasing the energy of the 3dd excited state relative to that of the luminescent metal-to-ligand charge transfer (MCLT) state.29,30 In contrast to the many spectroscopic investigations that have been carried out on immobilized dyes,1 comparatively less work has focused on elucidating photoinduced reactions between multiple components entrapped in solids.22,31-33 Although photoinduced energy transfer from Ru(bpy)32+ to Os(bpy)32+ is a well-established process, most studies that have reported on this process have been performed in solution with covalently linked binuclear systems.28,34 We are currently interested in the investigation of photoinduced energy and electron-transfer reactions of photoactive compounds inserted in the interlayer spaces of γ-zirconium phosphate (γ-ZrP). This material offers a (20) Vliers, D.; Schoonheydt, R. A.; Schryjver, F. C. J. Chem. Soc., Faraday Trans 1 1985, 81, 2009-2019. (21) Vliers, D.; Collin, D.; Schoonheydt, R. A.; Schryjver, F. C. Langmuir 1986, 2, 165-169. (22) Kumar, C. V.; Williams, Z. J.; Turner, R. S. J. Phys. Chem. A 1998, 102, 5562-5568. (23) (a) Byrd, H.; Clearfield, A.; Poojary, D.; Reis, K. P.; Thompson, M. E. Chem. Mater. 1996, 8, 2239-2246. (b) Poojary, D. M.; Vermeulen, L. A.; Vicenzi, E.; Clearfield, A.; Thompson, M. E. Chem. Mater. 1994, 6, 1845-1849. (c) Vermeulen, L. A.; Thompson, M. E. Chem. Mater. 1994, 6, 77-81. (d) Snover, J. L.; Thompson, M. E. J. Am. Chem. Soc. 1994, 116, 765-766. (e) Vermeulen, L. A.; Snover, J. L.; Sapochak, L. S.; Thompson, M. E. J. Am. Chem. Soc. 1993, 115, 11767-11774. (24) (a) Das, S. K.; Dutta, P. K. Langmuir 1998, 14, 5121-5126. (b) Borja, M.; Dutta, P. K. Nature 1993, 362, 43-45. (25) (a) Krueger, J. S.; Mayer, J. E.; Mallouk, T. E. J. Am. Chem. Soc. 1988, 110, 8232-8234. (b) Yonemoto, E. H.; Kim, H.-N.; Schmehl, R. H.; Wallin, J. O.; (c) Shoulders, B. A.; Richardson, B. R.; Haw, J. F.; Mallouk, T. E. J. Am. Chem. Soc. 1994, 116, 10557-10563. (26) Sykora, M.; Kincaid, J. R. Nature 1997, 387, 162-164. (27) (a) Balzani, V.; Scandola, F. Supramolecular Photochemistry; Ellis Horwood: Chischester, U.K., 1991. (b) Balzani, V.; Scandola, F. Compr. Supramol. Chem. 1996, 10, 687-746. (c) Scandola, F.; Balzani, V. J. Chem. Educ. 1983, 60, 814-823. (28) Sauvage, J. P.; Collin, J. P.; Chambron, J. C.; Guillerez, S.; Coudret, C.; Balzani, V.; Barigelletti, F.; De Cola, L.; Flamigni, L. Chem. Rev. 1994, 94, 993-919. (29) (a) Szulbinski, W. S.; Manuel, D. J.; Kincaid, J. R. Inorg. Chem. 2001, 40, 3443-3447. (b) Szulbinski, W. S.; Kincaid, J. R. Inorg. Chem. 1998, 37, 5014-5020. (c) Bhuiyan, A. A.; Kincaid, J. R. Inorg. Chem. 1998, 37, 2525-2530. (30) Adelt, M.; Devenney, M.; Meyer, T. J.; Thompson, D. W.; Treadway, J. A. Inorg. Chem. 1998, 37, 2616-2617. (31) Otsuka, T.; Takahashi, N.; Fujigasaki, N.; Sekine, A.; Ohashi, Y.; Kaizu, Y. Inorg. Chem. 1999, 38, 1340-1347. (32) (a) Byrd, H.; Suponeva, E. P.; Bocarsly, A. B.; Thompson, M. E. Nature 1996, 380, 610-612. (b) Shinozaki, K.; Hotta, Y.; Otsuka, T.; Kaizu, Y. Chem. Lett. 1999, 101-102. (33) Breu, J.; Kratzer, C.; Yersin, H. J. Am. Chem. Soc. 2000, 122, 2548-2555. (34) De Cola, L.; Belser, P. Coord. Chem. Rev. 1998, 177, 301-346.
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distinct microenvironment for nanoscale organization of a broad variety of molecular compounds,35,36 allowing one to examine the effect of interlayer confinement on the efficiency of photoinduced processes between donors and acceptors. It is hoped that such studies will provide insight into how this medium influences the photochemical process relative to the same reaction in solution. The specific objective of this work is to determine the effect of covalent intercalation within γ-ZrP on the rate of photoinduced energy transfer between ruthenium and osmium tris-bipyridine derivatives. The γ-ZrP matrix is of interest as a platform for the construction of supramolecular photochemical systems for several reasons. First, the chromophores are covalently bound to the inorganic framework, rather than being ionexchanged, as is the case for other hosts such as silica7,10,14,30 or clays.1,11 Covalent attachment prevents diffusion within the layers, thereby minimizing the possibility for collisional encounter of the chromophores. Second, γ-ZrP has a well-defined structure that remains essentially unaltered after intercalation of organic phosphonate guest compounds.35,36 Third, bulky guests with large cross-sectional areas can be accommodated within the interlayer space of γ-ZrP. Furthermore, the guests can be intercalated under mild conditions by simply contacting γ-ZrP microcrystals with a solution of a suitable phosphonic acid guest.37 Finally, γ-ZrP is transparent in the near UV and visible regions. In this paper, we report the preparation and characterization of hybrid materials consisting of a γ-ZrP matrix that includes two covalently pillared dyes: a ruthenium tris-bipyridine complex as an excited-state energy donor and an osmium tris-bipyridine complex as an energy acceptor. Photoinduced energy transfer from the Ru(bpy)32+ donor to Os(bpy)32+ has been examined with steady-state and time-resolved luminescence measurements, and the rate dependence of this reaction as a function of the molar ratio of the two chromophores in the γ-ZrP matrix has been investigated. Results and Discussion Preparation of the Phosphonate-Substituted Bipyridine Complexes. This study required a 2,2′-bipyridine ligand that is functionalized with phosphonic acid groups in order to allow the metal complex chromophore to bond to the phosphate host. To satisfy this requirement, the bis-phosphonate-substituted ligand 138 was selected. The methylene group between the phosphonate and the pyridyl group was inserted to prevent alteration of the energies of the bipyridine π and π* orbitals by the strongly electron withdrawing phosphonate substituent. As a result, the photochemical properties of the phosphonatesubstituted complexes 4 and 5 are very similar to those of the well-studied parent complexes, Ru(bpy)32+ and Os(bpy)32+. Bipyridine diethyl phosphonate ester 1 was converted into the corresponding ruthenium or osmium tris-bipy(35) Clearfield, A. Progress in Inorganic Chemistry; Wiley: New York, 1998; Vol. 47. (36) (a) Alberti, G., Bein, T., Eds. Comprehensive Supramolecular Chemistry, Volume 7: Solid-State Supramolecular Chemistry: Twoand Three-Dimensional Inorganic Networks; Elsevier: Oxford, U.K., 1996. (b) Alberti, G. Compr. Supramol. Chem. 1996, 7, 151-187. (c) Alberti, G.; Casciola, M.; Costantino, U.; Vivani, R. Adv. Mater. (Weinheim, Ger.) 1996, 8, 291-303. (37) (a) Alberti, G.; Giontella, E.; Murcia-Mascaros, S.; Vivani, R. Inorg. Chem. 1998, 37, 4672-4676. (b) Alberti, G.; Giontella, E.; MurciaMascaros, S. Inorg. Chem. 1997, 36, 2844-2849. (38) Wang, Q.; Wang, L.; Yu, L. J. Am. Chem. Soc. 1998, 120, 1286012868.
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Odobel et al.
Figure 1. Preparation of the guest complexes 4 and 5. Table 1. Composition and Interlayer Spacings of Phosphonate Materials sample
composition of the solida
d spacing (Å)
Ru/Os ratio
γ-ZrP γ-ZrP/octylamine MAT 1 MAT 2 MAT 3 MAT 4 MAT 5 MAT 6
Zr(PO4)(H2PO4)‚2H2O Zr(PO4)(HPO4; H3N-(CH2)7-CH3) Zr(PO4)(H2PO4)0.8(Rubpy3)0.1‚1.4 H2O Zr(PO4)(H2PO4)0.8(Osbpy3)0.1‚2H2O Zr(PO4)(H2PO4)0.76(Rubpy3)0.06(Osbpy3)0.06‚1.8 H2O Zr(PO4)(H2PO4)0.76(Rubpy3)0.067(Osbpy3)0.053‚1.8 H2O Zr(PO4)(H2PO4)0.76(Rubpy3)0.073(Osbpy3)0.043‚1.8 H2O Zr(PO4)(H2PO4)0.76(Rubpy3)0.087(Osbpy3)0.031‚1.7 H2O
12.2 29.2 18.6 18.6 18.6 18.5 18.6 18.7
1 1:0.8 1:0.6 1:0.35
a Compositions determined by UV-visible absorption and liquid-phase details.
ridine complexes 2 and 3 by reaction with either cis-Ru(bpy)2Cl239,40 or cis-Os(bpy)2Cl2.41 During this reaction, substantial hydrolysis of the diethyl phosphonate groups occurred.42 To alleviate this problem, the reaction time was decreased, allowing isolation and purification of the diethyl phosphonate ester complexes. Hydrolysis of the phosphonate ester groups in 2 and 3 was accomplished in a subsequent step by refluxing the complex in hydrochloric acid solution, which afforded hygroscopic solids 4 and 5 in a quantitative yield (Figure 1). Intercalation of 4 and 5 in the Zirconium Phosphonate Framework and Characterization by Powder X-ray Diffraction. The intercalation of γ-ZrP is a well-known process, which proceeds according to a topotatic reaction.35-37 When the pillaring guest is a bisphosphonic acid, the reaction involves the replacement of two H2PO4- groups belonging to two adjacent lamellae, and it affords a pillared material in which each inorganic sheet is “linked” through the bis-phosphonate-substituted bipyridines. Direct exchange of γ-ZrP with phosphonate 4 or 5 under typical conditions (i.e., a refluxing mixture of 1/1 acetone/ water)37 led to very low levels of intercalation (i.e.,
