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State-Selective Electron Transfer in an Unsymmetric Acceptor-Zn(II)porphyrin-Acceptor Triad: Toward a Controlled Directionality of Electron Transfer from the Porphyrin S-2 and S-1 States as a Basis for a Molecular Switch
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Kemiska sektionen, Institutionen för fotokemi och molekylärvetenskap, Kemisk fysik.
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2010 (Engelska)Ingår i: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 114, nr 4, s. 1709-1721Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

A series of Zn(II) porphyrin (ZnP) compounds covalently linked to different electron acceptor units, naphthaleneimide (NI) and naphthalenedimide (NDI), are reported. The aim was to demonstrate a state-selective direction of electron transfer, where excitation to the lowest excited S-1 state of the porphyrin (Q-band excitation) would give electron transfer to the NDI unit, while excitation to the higher S-2 state (Soret-hand excitation) would give electron transfer to the NI unit. This would constitute a basis for an opto-electronic Switch in which the direction of electron transfer and the resulting dipole moment can be controlled by using light input of different color. Indeed, electron transfer from the S-1 state to NDI Occurred in solvents of both high and low polarity, whereas no electron transfer to NDI was observed from the S-2 state. With NI as acceptor instead, very rapid (tau = 200-400 fs) electron transfer from the S-2 state occurred in all solvents. This was followed by an ultrafast (tau approximate to 100 fs) recombination to Populate the porphyrin S-1 state in nearly quantitative yield. The charge-separated state ZnP+NI- was spectroscopically observed, and evidence was obtained that recombination Occurred from a vibrationally excited ("hot") ZnP+NI- state in the more polar solvents. In these solvents, the thermally relaxed ZnP+NI- state lies at lower energy than the S-1 state so that further charge separation occurred from S-1 to form ZnP+NI-. This resulted in a highly unusual "ping-pong" sequence where the reaction went back and forth between locally excited ZnP states and charge-separated states: S-2 double right arrow ZnP+NI"hot"- double right arrow S-1 double right arrow ZnP+NI- double right arrow S-0. The electron transfer dynamics and its solvent dependence are discussed, as well as the function of the present Molecules as molecular switches.

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2010. Vol. 114, nr 4, s. 1709-1721
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URN: urn:nbn:se:uu:diva-137404DOI: 10.1021/jp907824dISI: 000273948100015OAI: oai:DiVA.org:uu-137404DiVA, id: diva2:378303
Tillgänglig från: 2010-12-15 Skapad: 2010-12-15 Senast uppdaterad: 2022-01-28Bibliografiskt granskad

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