Circular dichroism screw sense

One may have a question of whether an optically active helical polymer obtained from an enantiopure monomer adopts a purely P- (or M-) screw sense helical main chain in solution at a given temperature, or is composed of an ensemble of pseudo-diastereomeric mixed helical motifs containing P- and M-screw senses. Fluorescence (FL) studies combined with circular dichroism (CD), UV, and NMR spectra of the main chain constitute a powerful probe in identifying the main chain chirality (screw sense, uniformity, and rigidity) and optical purity of helical polymers, since the photoexcited energy above... 

Although most polysilanes adopt main-chain helical structures, most of them do not show a preferred screw sense. Thus, if a helical polymer shows a preferred screw sense it can be either left-handed or right-handed type. These possibilities can be detected by CD (circular dichroism) spectroscopy. Thus, in regular optical absorption spectroscopy the extinction coefficient or molar absorptivity (e) is related to the absorbance (A), concentration (c) and path length of the detecting cell (1) by the famous Beer-Lambert s expression (see Eq. 7.17). 

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