Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 20, Issue 45, Pages 14690-14697Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201403744
Keywords
donor-acceptor systems; electron transfer; porphyrinoids; transient absorption spectroscopy
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Funding
- Joint Center of Excellence in Integrated Nano-Systems (JCIN) at King Abdulaziz City for Science and Technology (KACST) [34-946]
- Northwestern University (NU)
- Chemical Sciences, Geosciences, and Biosciences Division, Office of Basic Energy Sciences, DOE [DE-FG02-99ER14999]
- National Defense Science and Engineering Graduate Fellowship from the Department of Defense
- NU International Institute for Nanotechnology
- Camille and Henry Dreyfus Postdoctoral Program in Environmental Chemistry
- International Materials Institute for Solar Energy and Environment - National Science Foundation [DMR-0843962]
- ANSER Center, an Energy Frontier Research Center - U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-SC0001059]
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Understanding the mechanism of efficient photoinduced electron-transfer processes is essential for developing molecular systems for artificial photosynthesis. Towards this goal, we describe the synthesis of a donor-acceptor dyad comprising a zinc porphyrin donor and a tetracationic cyclobis(paraquat-p-phenylene) (CBPQT(4+)) acceptor. The X-ray crystal structure of the dyad reveals the formation of a dimeric motif through the intermolecular coordination between the triazole nitrogen and the central Zn metal of two adjacent units of the dyad. Photoinduced electron transfer within the dyad in MeCN was investigated by femtosecond and nanosecond transient absorption spectroscopy, as well as by transient EPR spectroscopy. Photoexcitation of the dyad produced a weakly coupled ZnP+.-CBPQT(3+.) spin-correlated radical-ion pair having a =146ns lifetime and a spin-spin exchange interaction of only 0.23mT. The long radical-ion-pair lifetime results from weak donor-acceptor electronic coupling as a consequence of having nine bonds between the donor and the acceptor, and the reduction in reorganization energy for electron transfer caused by charge dispersal over both paraquat units within CBPQT(3+.).
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