Ultrafast light induced dissociation of Ru(dcbpy) (CO)₂I₂ in solution
Julkaistu sarjassa
Research report / Department of Chemistry, University of JyväskyläTekijät
Päivämäärä
2004
2024:58 | 2025:3
The research presented in this thesis focuses on the characterization of a detailed mechanism of the light induced ligand exchange reaction of (trans-I)Ru(dcbpy)(CO)2I2, (dcbpy= 4,4'-dicarboxy-2,2'-bipyridine). Illumination of Ru(dcbpy)I2(CO)2 with (near)ultraviolet light (UV) induces dissociation of one of the CO groups of the complex. In solution the opened coordination site of the metal is occupied by a solvent molecule. The starting point of this work was structural and spectral characterization of both the reactant and the product complexes and their electronic states. The main experimental technique utilized was transient absorption spectroscopy. The parent molecules were excited with a UV pulse and the dynamics of the ongoing reaction was recorded in the visible and in the infrared spectral regions. Based on the results of these measurements and quantum chemical calculations the following model for the ligand exchange reaction is suggested. The UV photon at 320 nm prepares the molecule in a dcbpy ligand centered π* ← π state. From this state internal conversion to a lower lying bound state and a repulsive state takes place with a time constant of few tens of fs. Dissociation was considered to have taken place when the CO group has escaped from the first solvation shell. Dissociation competes with geminate recombination and the observed rate constant of 1/62 rs-1 is a sum of these two processes. After dissociation ligands of the five-coordinated intermediate rearrange. An iodine ligand occupying initially an axial site moves towards the vacant equatorial site with a time constant of 500 fs. Simultaneously to this a solvent molecule attaches to the opened axial site to form the final product (cis-I)Ru(dcbpy)(CO)(EtOH)I2. Only an excitation wavelength dependent fraction of the excited molecules form the final product. The rest recombine with the five-coordinated intermediate due to cage effect provided by the solvent and reform the parent molecules in less than 170 fs. Also parallel internal conversion to non-reactive states decrease the quantum yield. In the picosecond timescale excess energy of the system undergoes intramolecular vibrational energy redistribution among the several vibrational modes of the newly born product and the recombined reactant and finally is dissipated as heat into the solvent environment. One important observation in this work was the survival of the excited state coherence over the duration of the dissociation reaction.
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ISBN
978-951-39-9976-6ISSN Hae Julkaisufoorumista
0357-346XJulkaisuun sisältyy osajulkaisuja
- Artikkeli I: Luukkanen, S., Haukka, M., Eskelinen, E., Pakkanen, T. A., Lehtovuori, V., Kallioinen, J., Myllyperkiö, P., & Korppi-Tommola, J. (2001). Photochemical reactivity of halogen-containing ruthenium-dcbpy (dcbpy-4,4'-dicarboxylic acid-2,2'-bipyridine compounds, trans(Br)-[Ru(dcbpy)(CO)Br2] and trans(I)-[Ru(dcbpy)(CO)2I2]. Phys.Chem.Chem.Phys., 3(11), 1992-1998. DOI: 10.1039/B100659M
- Artikkeli II: Lehtovuori, V., Kallioinen, J., Myllyperkiö, P., Korppi-Tommola, J., & Haukka, M. (2003). Effects of ligand substitution on the excited state dynamics of the Ru(dcbpy)(CO)2I2. Chemical Physics, 295, 81-88. DOI: 10.1016/j.chemphys.2003.08.008
- Artikkeli III: Lehtovuori, V., Aumanen, J., Myllyperkiö, P., Rini, M., Nibbering, E. T., & Korppi-Tommola, J. (2004). Transient Mid-IR Study of Light Induced Dissociation Reaction of Ru(dcbpy)CO2I2 in Solution. Journal of Physical Chemistry A, 108, 1644-1649. DOI: 10.1021/jp036492u
- Artikkeli IV: Lehtovuori, V., Myllyperkiö, P., Linnanto, J., Manzoni, C., Polli, D., Cerullo, G., Haukka, M., & Korppi-Tommola, J. (2005). Study of mechanisms of light-induced dissociation of Ru(dcbpy)(CO)2I2 in solution down to 20 fs time resolution. J. Phys. Chem. B., 109, 17538 - 17544. DOI: 10.1021/jp044735s
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