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14989665

Source:http://linkedlifedata.com/resource/pubmed/id/14989665

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pubmed-article:14989665pubmed:issue5lld:pubmed
pubmed-article:14989665pubmed:dateCreated2004-3-1lld:pubmed
pubmed-article:14989665pubmed:abstractTextThe characters, dynamics, and relaxation pathways of low-lying excited states of the complexes [W(CO)(5)L] [L = 4-cyanopyridine (pyCN) and piperidine (pip)] were investigated using theoretical and spectroscopic methods. DFT calculations revealed the delocalized character of chemically and spectroscopicaly relevant molecular orbitals and the presence of a low-lying manifold of CO pi-based unoccupied molecular orbitals. Traditional ligand-field arguments are not applicable. The lowest excited states of [W(CO)(5)(pyCN)] are W --> pyCN MLCT in character. They are closely followed in energy by W --> CO MLCT states. Excitation at 400 or 500 nm populates the (3)MLCT(pyCN) excited state, which was characterized by picosecond time-resolved IR and resonance Raman spectroscopy. Excited-state vibrations were assigned using DFT calculations. The (3)MLCT(pyCN) excited state is initially formed highly excited in low-frequency vibrations which cool with time constants between 1 and 20 ps, depending on the excitation wavelength, solvent, and particular high-frequency nu(CO) or nu(CN) mode. The lowest excited states of [W(CO)(5)(pip)] are W --> CO MLCT, as revealed by TD-DFT interpretation of a nanosecond time-resolved IR spectrum that was measured earlier in a low-temperature glass (Johnson, F. P. A.; George, M. W.; Morrison, S. L.; Turner, J. J. J. Chem. Soc., Chem. Commun. 1995, 391-393). MLCT(CO) excitation involves transfer of electron density from the W atom and, to a lesser extent, the trans CO to the pi orbitals of the four cis CO ligands. Optical excitation into MLCT(CO) transition of either complex in fluid solution triggers femtosecond dissociation of a W-N bond, producing [W(CO)(5)(solvent)]. It is initially vibrationally excited both in nu(CO) and anharmonicaly coupled low-frequency modes. Vibrational cooling occurs with time constants of 16-22 ps while the intramolecular vibrational energy redistribution from the v = 1 nu(CO) modes is much slower, 160-220 ps. No LF excited states have been found for the complexes studied in a spectroscopically relevant range up to 6-7 eV. It follows that spectroscopy, photophysics, and photochemistry of [W(CO)(5)L] and related complexes are well described by an interplay of close-lying MLCT(L) and MLCT(CO) excited states. The high-lying LF states play only an indirect photochemical role by modifying potential energy curves of MLCT(CO) states, making them dissociative.lld:pubmed
pubmed-article:14989665pubmed:languageenglld:pubmed
pubmed-article:14989665pubmed:journalhttp://linkedlifedata.com/r...lld:pubmed
pubmed-article:14989665pubmed:statusPubMed-not-MEDLINElld:pubmed
pubmed-article:14989665pubmed:monthMarlld:pubmed
pubmed-article:14989665pubmed:issn0020-1669lld:pubmed
pubmed-article:14989665pubmed:authorpubmed-author:MatousekPavel...lld:pubmed
pubmed-article:14989665pubmed:authorpubmed-author:ZálisStanisla...lld:pubmed
pubmed-article:14989665pubmed:authorpubmed-author:VlcekAntonínA...lld:pubmed
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pubmed-article:14989665pubmed:authorpubmed-author:BusbyMichaelMlld:pubmed
pubmed-article:14989665pubmed:authorpubmed-author:KotrbaTomásTlld:pubmed
pubmed-article:14989665pubmed:issnTypePrintlld:pubmed
pubmed-article:14989665pubmed:day8lld:pubmed
pubmed-article:14989665pubmed:volume43lld:pubmed
pubmed-article:14989665pubmed:ownerNLMlld:pubmed
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pubmed-article:14989665pubmed:pagination1723-34lld:pubmed
pubmed-article:14989665pubmed:year2004lld:pubmed
pubmed-article:14989665pubmed:articleTitleExcited-state characters and dynamics of [W(CO)(5)(4-cyanopyridine)] and [W(CO)(5)(piperidine)] studied by picosecond time-resolved IR and resonance Raman spectroscopy and DFT calculations: roles of W --> L and W --> CO MLCT and LF excited states revised.lld:pubmed
pubmed-article:14989665pubmed:affiliationJ. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Dolejskova 3, CZ-182 23 Prague, Czech Republic.lld:pubmed
pubmed-article:14989665pubmed:publicationTypeJournal Articlelld:pubmed