TY - JOUR
T1 - Conformationally gated switching between superexchange and hopping within oligo-p-phenylene-based molecular wires
AU - Weiss, Emily A.
AU - Tauber, Michael J.
AU - Kelley, Richard F.
AU - Ahrens, Michael J.
AU - Ratner, Mark A.
AU - Wasielewski, Michael R.
PY - 2005/8/24
Y1 - 2005/8/24
N2 - We observe well-defined regions of superexchange and thermally activated hopping in the temperature dependence of charge recombination (CR) in a series of donor-bridge-acceptor (D-B-A) systems, where D = phenothiazine (PTZ), B = p-phenylene (Phn), n = 1-4, and A = perylene-3,4:9,10- bis(dicarboximide) (PDI). A fit to the thermally activated CR rates of the n = 3 and n = 4 compounds yields activation barriers of 1290 and 2030 cm -1, respectively, which match closely with theoretically predicted and experimentally observed barriers for the planarization of terphenyl and quaterphenyl. Negative activation of CR in the temperature regions dominated by superexchange charge transport is the result of a fast conformational equilibrium that increasingly depopulates the reactive state for CR as temperature is increased. The temperature dependence of the effective donor-acceptor superexchange coupling, VDA, measured using magnetic field effects on the efficiency of the charge recombination process, shows that CR occurs out of the conformation with lower VDA via the energetically favored triplet pathway.
AB - We observe well-defined regions of superexchange and thermally activated hopping in the temperature dependence of charge recombination (CR) in a series of donor-bridge-acceptor (D-B-A) systems, where D = phenothiazine (PTZ), B = p-phenylene (Phn), n = 1-4, and A = perylene-3,4:9,10- bis(dicarboximide) (PDI). A fit to the thermally activated CR rates of the n = 3 and n = 4 compounds yields activation barriers of 1290 and 2030 cm -1, respectively, which match closely with theoretically predicted and experimentally observed barriers for the planarization of terphenyl and quaterphenyl. Negative activation of CR in the temperature regions dominated by superexchange charge transport is the result of a fast conformational equilibrium that increasingly depopulates the reactive state for CR as temperature is increased. The temperature dependence of the effective donor-acceptor superexchange coupling, VDA, measured using magnetic field effects on the efficiency of the charge recombination process, shows that CR occurs out of the conformation with lower VDA via the energetically favored triplet pathway.
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U2 - 10.1021/ja052901j
DO - 10.1021/ja052901j
M3 - Article
C2 - 16104763
AN - SCOPUS:23944477885
VL - 127
SP - 11842
EP - 11850
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 33
ER -