Rb. Prince et al., Cooperativity in the folding of helical m-phenylene ethynylene oligomers based upon the 'Sergeants-and-Soldiers' principle, CHEM-EUR J, 7(19), 2001, pp. 4150-4154
The 'Sergeants-and-Soldiers' principle has been examined in a series of m-p
henylene ethynylene oligomers containing both chiral and achiral side chain
s. Circular dichroism (CD) spectroscopy was used to examine the twist sense
bias of the helical conformation in the polar solvent acetonitrile. A nonl
inear dependence of the CD signal on the amount of chiral side chains was o
bserved revealing cooperative interactions among the side chains through th
e backbone. On the other hand, the experiments indicate that in acetonitril
e a full bias of the helicity cannot be accomplished by chiral side chains
alone. Nevertheless, the folded oligomers are highly ordered since the plac
ement of a single chiral side chain at the beginning of an oligomer results
in the induction of a strong twist sense bias into the ordered helical con
formation.