TY - JOUR
T1 - Helical Oligoenes
T2 - Conformations, Bond Alternation, and Competing Through-Bond and Through-Space Transmission
AU - Tsuji, Yuta
AU - Hoffmann, Roald
N1 - Publisher Copyright:
© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
PY - 2016/3/24
Y1 - 2016/3/24
N2 - There is a consensus that long-range electron transfer/transport occurs by a through-bond rather than through-space mechanism. In helical all-Z, all-s-cis oligoenes, one can set up an interesting competition in the medium-separation regime between a closer (in distance) through-space path and a more distant through-bond one. Although such oligoene conformations/isomers are unstable (by around 4 kcal mol-1 per double bond relative to all-E, all-s-trans isomers), recent synthetic efforts on truncated helicenes and oligothiophenes have provided related molecules. On the way to transmission calculations with electrodes attached to the termini of helical oligoenes, we uncover an interesting conformational ambiguity in all-Z, all-s-cis oligoenes, the existence of a broad conformational minimum for helical compression, with hints of end-to-end frontier-orbital-caused stabilization. There is relationship between helical oligoene structures and the corresponding substructure of a helicene, but there are also significant differences in the number of olefin subunits per helix turn. In Hückel transport calculations, the role of TB or TS mechanisms is obscured to an extent by variations in bond alternation and dihedral angle along the oligomer chain. However, the operation of a dominant through bond mechanism emerges clearly in local transmission plots. In moving the electrodes to carbon position related by quantum interference, it is possible to uncover a through space mechanism.
AB - There is a consensus that long-range electron transfer/transport occurs by a through-bond rather than through-space mechanism. In helical all-Z, all-s-cis oligoenes, one can set up an interesting competition in the medium-separation regime between a closer (in distance) through-space path and a more distant through-bond one. Although such oligoene conformations/isomers are unstable (by around 4 kcal mol-1 per double bond relative to all-E, all-s-trans isomers), recent synthetic efforts on truncated helicenes and oligothiophenes have provided related molecules. On the way to transmission calculations with electrodes attached to the termini of helical oligoenes, we uncover an interesting conformational ambiguity in all-Z, all-s-cis oligoenes, the existence of a broad conformational minimum for helical compression, with hints of end-to-end frontier-orbital-caused stabilization. There is relationship between helical oligoene structures and the corresponding substructure of a helicene, but there are also significant differences in the number of olefin subunits per helix turn. In Hückel transport calculations, the role of TB or TS mechanisms is obscured to an extent by variations in bond alternation and dihedral angle along the oligomer chain. However, the operation of a dominant through bond mechanism emerges clearly in local transmission plots. In moving the electrodes to carbon position related by quantum interference, it is possible to uncover a through space mechanism.
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U2 - 10.1002/chem.201600042
DO - 10.1002/chem.201600042
M3 - Article
AN - SCOPUS:84976237154
VL - 22
SP - 4878
EP - 4888
JO - Chemistry - A European Journal
JF - Chemistry - A European Journal
SN - 0947-6539
IS - 14
ER -