Helical springs as a color indicator for determining chirality and enantiomeric excess

Abstract

Chirality plays a key role in the physiological system, because molecular functionalities may drastically alter due to a change in chirality. We report herein a unique color indicator with a static helicity memory, which exhibits visible color changes in response to the chirality of chiral amines. A difference of less than 2% in the enantiomeric excess (ee) values causes a change in the absorption that is visible to the naked eyes. This was further quantified by digital photography by converting to RGB values. This system relies on the change in the tunable helical pitch of the π-conjugated polymer backbone in specific solvents and allows rapid on-site monitoring of chirality of nonracemic amines, including drugs, and the simultaneous quantitative determination of their ee values.

Dissymmetric Chiral Poly(diphenylacetylene)s: Secondary Structure Elucidation and Dynamic Luminescence

“…It is commonly applied to assess cis‐ or trans‐ content in PPAs and PDPAs [51, 99, 100] . Catalysts based on tungsten (W) are known to provide trans ‐rich PDPAs as shown in many examples in the literature, [99, 100] albeit Maeda recently demonstrated that in the case of symmetric PDPAs, polyene backbones with a predominant cis‐ content of double bonds are also obtained [79, 80] …”

“…Another interesting family of helical polymers are the poly(diphenylacetylene)s (PDPAs) [71–93] that resemble PPAs in the main chain, which in both cases is made up of conjugated double bonds. However, the presence of a phenyl group on each carbon of the double bond in PDPAs makes the properties of both materials very different.…”

Dissymmetric Chiral Poly(diphenylacetylene)s: Secondary Structure Elucidation and Dynamic Luminescence

“…[51,99,100] Catalysts based on tungsten (W) are known to provide trans-rich PDPAs as shown in many examples in the literature, [99,100] albeit Maeda recently demonstrated that in the case of symmetric PDPAs, polyene backbones with a predominant cis-content of double bonds are also obtained. [79,80] Herein, we will study the stereoregularity of poly-1 and poly-(S)-2 by comparison of their Raman spectra with those obtained for PPAs with well-known secondary structure. Therefore, as model compounds we chose poly-(3-6) (Figure 2a).…”

“…For instance, PDPAs show better chemical, thermal and photochemical stability compared to PPAs. [72][73][74][75][76][77][78][79][80][81][82][83][84][85] Moreover, PDPAs exhibit another interesting property that PPAs do not have, i.e. photoluminescence.…”

“…[81,82,86,99] Recently, Maeda and co-workers studied the secondary structure of symmetric PDPAs bearing para-substituted carboxy pendant groups. [79,80] By using a combination of 1 H and 13 C NMR, IR, Raman, VCD and ECD spectroscopies, they found that this polymer adopts a preferred cis-transoidal structure, where P or M-helical senses can be induced by thermal annealing in water in the presence of chiral amines. On the other hand, in the case of asymmetric PDPAs, Kwak, Aoki and co-workers made great contributions to the study of their luminescent properties and to the achiral-to-chiral transformations of PDPAs.…”