@article{nieves-bernier_diers_taniguchi_holten_bocian_lindsey_2010, title={Probing the Rate of Hole Transfer in Oxidized Synthetic Chlorin Dyads via Site-Specific C-13-Labeling}, volume={75}, ISSN={["1520-6904"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-77952494274&partnerID=MN8TOARS}, DOI={10.1021/jo100527h}, abstractNote={Understanding electronic communication among interacting constituents of multicomponent molecular architectures is important for rational design in diverse fields including artificial photosynthesis and molecular electronics. One strategy for examining ground-state hole/electron transfer in an oxidized tetrapyrrolic array relies on analysis of the hyperfine interactions observed in the EPR spectrum of the pi-cation radical. This strategy has been previously employed to probe the hole/electron-transfer process in oxidized multiporphyrin arrays of normal isotopic composition, wherein (1)H and (14)N serve as the hyperfine "clocks", and in arrays containing site-specific (13)C-labels, which serve as additional hyperfine clocks. Herein, the hyperfine-clock strategy is applied to dyads of dihydroporphyrins (chlorins). Chlorins are more closely related structurally to chlorophylls than are porphyrins. A de novo synthetic strategy has been employed to introduce a (13)C label at the 19-position of the chlorin macrocycle, which is a site of large electron/hole density and is accessible synthetically beginning with (13)C-nitromethane. The resulting singly (13)C-labeled chlorin was coupled with an unlabeled chlorin to give a dyad wherein a diphenylethyne linker spans the 10-positions of the two zinc chlorins. EPR studies of the monocations of both the natural abundance and (13)C-labeled zinc chlorin dyads and benchmark zinc chlorin monomers reveal that the time scale for hole/electron transfer is in the 4-7 ns range, which is 5-10-fold longer than that in analogous porphyrin arrays. The slower hole/electron transfer rate observed for the chlorin versus porphyrin dyads is attributed to the fact that the HOMO is a(1u)-like for the chlorins versus a(2u)-like for the porphyrins; the a(1u)-like orbital exhibits little (or no) electron/hole density at the site of linker attachment whereas the a(2u)-like orbital exhibits significant electron/hole density at this site. Collectively, the studies of the chlorin and porphyrin dyads provide insights into the structural features that influence the hole/electron-transfer process.}, number={10}, journal={JOURNAL OF ORGANIC CHEMISTRY}, publisher={American Chemical Society (ACS)}, author={Nieves-Bernier, Elias J. and Diers, James R. and Taniguchi, Masahiko and Holten, Dewey and Bocian, David F. and Lindsey, Jonathan S.}, year={2010}, month={May}, pages={3193–3202} }