Mechanically induced intramolecular electron transfer in a mixed-valence molecular shuttle
The kinetics and thermodynamics of intramolecular electron transfer (IET) can be subjected to redox control in a bistable [2]rotaxane comprised of a dumbbell component containing an electron-rich 1,5-dioxynaphthalene (DNP) unit and an electron-poor phenylene-bridged bipyridinium (P-BIPY2+) unit and a cyclobis (paraquat-p-phenylene) (CBPQT4+) ring component. The [2]rotaxane exists in the ground-state co-conformation (GSCC) wherein the CBPQT4+ ring encircles the DNP unit. Reduction of the CBPQT4+ leads to the CBPQT2(•+) diradical dication while the P-BIPY2+ unit is reduced to its P-BIPY•+ radical cation. A radical-state co-conformation (RSCC) results from movement of the CBPQT2(•+) ring along the dumbbell to surround the P-BIPY•+ unit. This shuttling event induces IET to occur between the pyridinium redox centers of the P-BIPY•+ unit, a property which is absent between these redox centers in the free dumbbell and in the 1:1 complex formed between the CBPQT2(•+) ring and the radical cation of methyl-phenylene-viologen (MPV•+). Using electron paramagnetic resonance (EPR) spectroscopy, the process of IET was investigated by monitoring the line broadening at varying temperatures and determining the rate constant (kET = 1.33 × 107 s-1) and activation energy (ΔG‡ = 1.01 kcal mol-1) for electron transfer. These values were compared to the corresponding values predicted, using the optical absorption spectra and Marcus–Hush theory.
- Research Organization:
- Energy Frontier Research Centers (EFRC) (United States). Center for Bio-Inspired Energy Science (CBES)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES)
- DOE Contract Number:
- SC0000989
- OSTI ID:
- 1384548
- Journal Information:
- Proceedings of the National Academy of Sciences of the United States of America, Vol. 109, Issue 29; Related Information: CBES partners with Northwestern University (lead); Harvard University; New York University; Pennsylvania State University; University of Michigan; University of Pittsburgh; ISSN 0027-8424
- Publisher:
- National Academy of Sciences, Washington, DC (United States)
- Country of Publication:
- United States
- Language:
- English
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