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Ultrafast charge separation in a photoreactive rhenium-appended porphyrin assembly monitored by picosecond transient infrared spectroscopy.

Gabrielsson, A., Hartl, F., Zhang, H., Lindsay Smith, J.R., Towrie, M., Vlcek, A. and Perutz, R.N. (2006) Ultrafast charge separation in a photoreactive rhenium-appended porphyrin assembly monitored by picosecond transient infrared spectroscopy. Journal of the American Chemical Society, 128 (13). pp. 4253-4266. ISSN 0002-7863

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Abstract

Rhenium(bipyridine)(tricarbonyl)(picoline) units have been linked covalently to tetraphenylmetalloporphyrins of magnesium and zinc via an amide bond between the bipyridine and one phenyl substituent of the porphyrin. The resulting complexes, abbreviated as [Re(CO)3(Pic)Bpy-MgTPP][OTf] and [Re(CO)3(Pic)Bpy-ZnTPP][OTf], exhibit no signs of electronic interaction between the Re(CO)3(bpy) units and the metalloporphyrin units in their ground states. However, emission spectroscopy reveals solvent-dependent quenching of porphyrin emission on irradiation into the long-wavelength absorption bands localized on the porphyrin. The characteristics of the excited states have been probed by picosecond time-resolved absorption (TRVIS) spectroscopy and time-resolved infrared (TRIR) spectroscopy in nitrile solvents. The presence of the charge-separated state involving electron transfer from MgTPP or ZnTPP to Re(bpy) is signaled in the TRIR spectra by a low-frequency shift in the ν(CO) bands of the Re(CO)3 moiety similar to that observed by spectroelectrochemical reduction. Long-wavelength excitation of [Re(CO)3(Pic)Bpy-MTPP][OTf] results in characteristic TRVIS spectra of the S1 state of the porphyrin that decay with a time constant of 17 ps (M = Mg) or 24 ps (M = Zn). The IR bands of the CS state appear on a time scale of less than 1 ps (Mg) or ca. 5 ps (Zn) and decay giving way to a vibrationally excited (i.e., hot) ground state via back electron transfer. The IR bands of the precursors recover with a time constant of 35 ps (Mg) or 55 ps (Zn). The short lifetimes of the charge-transfer states carry implications for the mechanism of reaction in the presence of triethylamine.

Item Type: Article
Institution: The University of York
Academic Units: The University of York > Chemistry (York)
Depositing User: York RAE Import
Date Deposited: 03 Apr 2009 15:09
Last Modified: 03 Apr 2009 15:09
Published Version: http://dx.doi.org/10.1021/ja0539802
Status: Published
Publisher: ACS American Chemical Society
Identification Number: 10.1021/ja0539802
URI: http://eprints.whiterose.ac.uk/id/eprint/6888

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