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Title: Chain folding controlled by an isomeric repeat unit: helix formation versus random aggregation in acetylene-bridged carbazole-bipyridine co-oligomers
Authors: Divya, K P
Sreejith, S
Suresh, C H
Divya, S P
Ajayaghosh, A
Keywords: Phenylene ethynylene oligomers
Conjugated polyelectrolyte
Nonbiological oligomers
Organic nanotubes
Circular dichroism
Donor-acceptor systems
Helical structures
Issue Date: 2013
Publisher: Wiley
Citation: Chemistry- An Asian Journal 8(7):1579-1586;Jul 2013
Abstract: An unprecedented, positional effect of the isomeric repeat unit on chain folding in donor-acceptor-linked oligomers, which contain alternating bipyridine and carbazole moieties that are connected through an acetylinic linkage, is reported. 4,4-Linked oligomer 1 adopts an intrachain helical conformation (CD-active) in CHCl3/MeCN (20:80 v/v), whereas oligomer 2, which contains an isomeric 6,6-linkage, forms interchain randomly coiled aggregates (CD-inactive). The substitution position plays a significant role in controlling the variations in electronic effects and dipole moments around the bipyridyl moiety, which are responsible for this observed phenomenon. Two model compounds of oligomers 1 and 2 (3 and 4, respectively) were prepared and their properties were compared. A systematic investigation of the photophysical and CD properties of these structures, as well as theoretical studies, support our conclusions.
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