Abstract
Continuous-wave time-resolved electron spin resonance (TRESR) spectroscopy has been successfully employed to elucidate photochemical reaction mechanisms, since chemically induced dynamic electron polarization (CIDEP) spectra observed give information about the spin dynamics of short-lived intermediates such as radical pairs (RPs) and free radicals (FRs) [1–3]. CIDEP spectra were usually interpreted by two main mechanisms: triplet mechanism (TM) and radical pair mechanism (RPM). In the TM, electron spin polarization (ESP), which existed in the excited triplet state, is transferred to each of the radicals created on its reaction. The intersystem crossing (ISC) process is usually spin-selective and produces the excited triplet state with a non-equilibrated population in the spin sublevels, spin polarized triplet state. When a reaction occurs from such a polarized triplet state before the relaxation, spin-polarized radicals are produced, generating net polarized CIDEP spectra. In this paper we describe CIDEP phenomena for the photoredox reaction between the polyoxometalate (POM) and both electron- and proton-donor (DH), which allows us to detect large emissive ESP of deproto- nated one-electron oxidized species (D•) generated by the electron transfer (with an accompanying transfer of proton) from DH to the oxygen-to-metal charge transfer (O→M LMCT) excited triplet states of POM (3(O→M LMCT)), and to investigate the primary processes of the solution chemistry of POM [4]. If the photoredox reaction between POM and DH occurs rapidly via3(O→M LMCT), ESP in the 3(O→M LMCT) can be expected to be transferred to D• and /or POM- H (one-electron reduced protonated species of POM) to give rise to CIDEP To be observed, the production of D• must rapidly take place before thermal equilibrium of the triplet spin-lattice relaxation of3(O→M LMCT) has been established. The TM seems to be common in the photoredox reactions of POMs which produce emissive ESP in elementary steps.
This is a preview of subscription content, log in via an institution.
Buying options
Tax calculation will be finalised at checkout
Purchases are for personal use only
Learn about institutional subscriptionsPreview
Unable to display preview. Download preview PDF.
References
McLauchlan, K.A. (1985) Flash Photolysis Electron Spin Resonance, Chem. Britain, 25.
McLauchlan, K.A. and Stevens, D.G. (1988) Flash Photolysis Electron Spin Resonance, Ace. Chem. Res. 21, 54.
Turro, N.J., Kleinmann, M.H. and Karatekin, E. (2000) Electron Spin Polarization and Time-Resolved Electron Paramagnetic Resonance: Applications to the Paradigms of Molecular and Supramolecular Photochemistry, Angew. Chem. Int. Ed. 39, 4436.
Yamase, T. and Ohtaka, K. (1994) Photochemistry of Polyoxovanadates. Part 1. Formation of the Anion-encapsulatedPolyoxovanadate [V15O36(CO3)]7- and Electron-Spin Polarization of α-Hydroxyalkyl Radicals in the Presence of Alcohols, J. Chem. Soc. Dalton Trans., 2599.
Yamase, T. (1985) Photochemistry of Polyoxometalates as Homogeneous Photocatalysts for Redox Reactions of Organic Molecules, J. Synt. Org. Chem. Jpn. 43, 1249.
Yamase, T. (1993) Photocatalytic Activity of Polyoxometalates in Homogeneous Systems in T. Kudoh, T. Okuhara, K. Matsumoto, and T. Yamase (eds.), Polyoxometalate Chemistry, Gakkai Shuppan Center Kikan Kagaku Sosetsu 20, p. 199.
Papaconstantinou, E. (1989) Photochemistry of Polyoxometallates of Molybdenum and Tungsten and/or Vanadium, Chem. Soc. Rev. 18, 1.
Hill, C.L. and Prosser-McCartha, CM. (1993) Photocatalytic and Photoredox Properties of Polyoxometalate Systems in K. Kalyanasundaram and Grätzel (eds.), Photosensitization and Photo catalysis Using Inorganic and Organometallic Compounds, Kluwer Academic Publishers, p.307.
Kraut, B. and Ferraudi, G. (1989) Intermediates in the Early Events of Mo7O228-1 Catalyzed Photodehydrogenations: A Picosecond-Nanosecond Flash-Photochemical Study, Inorg. Chem. 28, 2692.
Tanielian, C., Duffy, K. and Jones, A. (1997) Kinetic and Mechanistic Aspects of Photocatalysis by Polyoxotungstates: A Laser Flash Photolysis, Pulse Radiolysis, and Continuous Photolysis Study, J. Phys. Chem. B 101, 4276.
T. Yamase, T. (1991) Photochemical Studies of Alkylammonium Molybdates. Part 9. Structure of Diamagnetic Blue Species Involved in the Photoredox Reaction of [Mo7O24]6-, J. Chem. Soc. Dalton Trans., 3055.
Yamase, T., Yang, L. and Suzuki, R. (1999) Photochemically Self-assembly Reactions of Polyoxovanadates. Structure of [MoO4]2”-Encapsulated Mixed-valent Cluster [V22O54(MoO4)]8” and Template-exchange Reaction of [V18O42(H2O)]12-, J. Mol. Catal. A, 147, 179.
Yamase, T. and Ishikawa, E. (2000) Photochemical Self-assembly Reaction ofβ-[Mo8O26]4- to Mixed-valence Cluster [Mo37O112]26- in Aqueous Media, Langmuir 16, 9023.
Yamase, T. and Prokop, P. (2002) Photochemical Formation of Tire-shaped Molybdenum Blues: Topology of a Defect Anion, [Mo142O432H28(H2O)58]12-, Angew. Chem. Int. Ed. Engl. 41, 466.
Yamase, T. and Ikawa, T. (1979) Photogalvanic Effect in Alkylammonium Molybdate Solutions and Production of Hydrogen, Inorg. Chim. Acta 27, L529.
Yamase, T. (1983) Water Splitting by Photoirradiation of Alkylammonium Polytungstates in Homogeneous Solutions and Detectable Paramagnetic Species, Inorg. Chim. Acta, 76, L25.
Yamase, T. and Watanabe, R. (1983) Photochemical Hydrogen-Evolution from Alkaline Solution of Alkylammonium Isopolyvanadate, Inorg. Chim. Acta 11, LI93.
Yamase, T., Takabayashi, N. and Kaji, M. (1984) Solution Photochemistry of Tetrakis(tetrabutylammonium) Decatungstate(VI) and Catalytic Hydrogen Evolution from Alcohols, J. Chem. Soc. Dalton Trans., 793.
Yamase, T. and Watanabe, R. (1986) Photoredox Chemistry of Keggin Dodecatungstoborate and Role of Heterogeneous Catalysis for Hydrogen Formation, J. Chem. Soc. Dalton Trans., 1669.
Yamase, T. and M. Sugeta (1993) M. Charge-Transfer Typed Photoluminescence of Polyoxometalates of Tungsten and Molybdenum, J. Chem. Soc. Dalton Trans., 759.
Blättler, C.B., Jent, F. and Paul, H. (1990) A Novel Radical-Triplet Pair Mechanism for Chemically Induced Electron Polarization (CIDEP) of Free Radical in Solution, Chem. Phys. Lett. 166, 375.
Kawai, A., Okutsu, T. and Obi, K. (1991) Spin Polarization Generated in the Triplet-Doublet Interaction: Hyperfine-Dependent Chemically Induced Dynamic Electron Polarization, J. Phys. Chem. 95,9130.
Yamase, T. (1998) Photo-and Electrochromism of Polyoxometalate s and Related Materials, Chem. Rev., 98, 307.
Bartels, D.M., Lawler, R.G. and Trifunac, A.D. (1985) Electron T1 measurements in Shortlived Free Radicals by Dynamic Polarization Recovery, J. Chem. Phys. 83, 2686.
Yamase, T. Unpublished results in paper preparation.
Yamase, T. and Kurozumi, T. (1983) Photoreduction of Polymolybdates(VI) in Aqueous Solution Containing Acetic Acid, J. Chem. Soc. Dalton Trans., 2205.
Yamase, T. (1978) Photochemical Studies of the Alkylammonium Molybdates. Part 4. Electron Spin Resonance Study of an Irradiated Single Crystal of Hexakis(isopropylammonium)dihydrogen Octamolybdate Dihydrate, J. Chem. Soc. Dalton Trans., 283.
Yamase, T. and Suga, M. (1989) Photochemical Studies of Alkylammonium Molybdates. Part 8. Location of Protons Interacting with Paramagnetic Electron in a Single Crystal of Photoirradiated [NH3Pri]6[Mo8O26(OH)2]-2H2O, J. Chem. Soc. Dalton Trans., 661.
Yamase, T., Sasaki, R. and Ikawa, T. (1981) Photochemical Studies of the Alkylammonium Molybdates. Part 5. Photolysis in Weak Acid Solutions, J. Chem. Soc. Dalton Trans., 628.
Yamase, T. (1985) Photochemical Studies of the Alkylammonium Molybdates. Part 7. Octahedral Sites for Multi-electron Reduction of [Mo8O26(MoO4)2]8-, J. Chem. Soc. Dalton Trans., 2585.
Author information
Authors and Affiliations
Editor information
Editors and Affiliations
Rights and permissions
Copyright information
© 2003 Springer Science+Business Media Dordrecht
About this chapter
Cite this chapter
Yamase, T. (2003). Time-Resolved Electron Spin Resonance Spectroscopy of Photoredox Reactions of Polyoxometalates: Formation of Paramagnetic-Species Pair by Triplet Mechanism. In: Borrás-Almenar, J.J., Coronado, E., Müller, A., Pope, M. (eds) Polyoxometalate Molecular Science. NATO Science Series, vol 98. Springer, Dordrecht. https://doi.org/10.1007/978-94-010-0091-8_6
Download citation
DOI: https://doi.org/10.1007/978-94-010-0091-8_6
Publisher Name: Springer, Dordrecht
Print ISBN: 978-1-4020-1242-6
Online ISBN: 978-94-010-0091-8
eBook Packages: Springer Book Archive