One‐Handed Helical Tubular Ladder Polymers for Chromatographic Enantioseparation**

Abstract

Defect‐free one‐handed contracted helical tubular ladder polymers with a π‐electron‐rich cylindrical helical cavity were synthesized by alkyne benzannulations of the random‐coil precursor polymers containing 6,6′‐linked‐1,1′‐spirobiindane‐7,7′‐diol‐based chiral monomer units. The resulting tightly‐twisted helical tubular ladder polymers showed remarkably high enantioseparation abilities toward a variety of chiral hydrophobic aromatics with point, axial, and planar chiralities. The random‐coil precursor polymer and analogous rigid‐rod extended helical ribbon‐like ladder polymer with no internal helical cavity exhibited no resolution abilities. The molecular dynamics simulations suggested that the π‐electron‐rich cylindrical helical cavity formed in the tightly‐twisted tubular helical ladder structures is of key importance for producing the highly‐enantioseparation ability, by which chiral aromatics can be enantioselectively encapsulated by specific π‐π and/or hydrophobic interactions.

Defect-Free Synthesis of a Fully π-Conjugated Helical Ladder Polymer and Resolution into a Pair of Enantiomeric Helical Ladders

“…Based on the time-dependent-density functional theory calculations of a (P)-handed helical oligomer model ((P)-model-a) (Figure S30), the helical sense of the poly-8Me (f1-f7) showing the positive and negative Cotton effect signs at 410 and 360 nm, respectively (Figure 4b(i-vii)), was assigned to the (P)-helix, and hence, the (M)-helix for the latter fractions (f8-f10) (Figure 4b(viiix)). Although the helix-sense excess (hse) values of the fractionated poly-8Me samples remain unsolved, the Kuhn's dissymmetry factor (gabs) of the fractionated poly-8Me (f1) reached 1.7 × 10 -2 at a maximum (Figure 4b(i)), which is sufficiently high comparable to or exceeding those of the previously reported conjugated one-handed helical polymers, including polyisocyanides, polyisocyanates, polyacetylenes, and polysilanes, [23] as well as the partially conjugated one-handed helical ladder polymers (poly-A, [15] poly-B, [16] and poly-C [17] ) (typically in the order of 10 −3 ). As a result, the hse value of the poly-8Me (f1) is presumed to be rather high (Figure 4b(i)).…”

“…[13] Recently, Nuckolls and coworkers reported unique single-handed fully p-conjugated helical ladder polymers (helicene nanoribbons), which were, however, achieved by using a configurationally stable right (P)-or left (M)-handed-[6]helicene as the chiral framework. [14] We recently succeeded in the defect-free synthesis of "partially conjugated" one-handed helical (poly-A, [15] poly-B, [16] and poly-C [17] ) (Figure 1a) and "fully p-conjugated" achiral zigzag coplanar ladder polymers. [17] The overall 3D ladder geometry can be controlled by a combination of chiral/achiral (Figure 1a) and achiral/achiral comonomer units of the random-coil precursor polymers containing the same achiral 2,5-diethynyl-substituted pphenylene segments, followed by acid-promoted intramolecular alkyne benzannulations.…”

“…The helical handedness ((P)-or (M)helix) and helical pitch (contracted or extended helix) of the helical ladder polymers are determined by the enantiopure 2,6-linkedtriptycene and 6,6´-and 4,4´-linked-1,1´-spirobiindane units (Figure 1a). The quantitative [18] and chemoselective [16][17] acidpromoted alkyne benzannulations of the precursor polymers are of key importance, which relies on the 2,6-dimethyl substituents introduced on the phenylethynyl pendant groups [16][17] except for the bulky triptycene-bound poly-A. [15] Here, we show that a rationally designed precursor polymer composed of alternating achiral 2,7-linked-fluorene and 2,4diethynyl-substituted C2v-symmetric m-phenylene units is quantitatively and chemoselectively converted into a fully pconjugated ladder polymer with a spiral geometry through the acid-promoted annulative p-extension (Figure 1b).…”

Defect‐Free Synthesis of a Fully π‐Conjugated Helical Ladder Polymer and Resolution into a Pair of Enantiomeric Helical Ladders**

“…[13] Recently, Nuckolls and co-workers reported unique single-handed fully π-conjugated helical ladder polymers (helicene nanoribbons), which were, however, achieved by using a configurationally stable right (P)or left (M)-handed- [6]helicene as the chiral framework. [14] We recently succeeded in the defect-free synthesis of "partially conjugated" one-handed helical (poly-A, [15] poly-B, [16] and poly-C [17] ) (Figure 1a) and "fully π-conjugated" achiral zigzag coplanar ladder polymers. [17] The overall 3D ladder geometry can be controlled by a combination of chiral/achiral (Figure 1a) and achiral/achiral comonomer units of the random-coil precursor polymers containing the same achiral 2,5-diethynyl-substituted p-phenylene segments, followed by acid-promoted intramolecular alkyne benzannulations.…”

“…The helical handedness ((P)-or (M)-helix) and helical pitch (contracted or extended helix) of the helical ladder polymers are determined by the enantiopure 2,6-linked-triptycene and 6,6'-and 4,4'-linked-1,1'-spirobiindane units (Figure 1a). The quantitative [18] and chemoselective [16,17] acid-promoted alkyne benzannulations of the precursor polymers are of key importance, which relies on the 2,6-dimethyl substituents introduced on the phenylethynyl pendant groups [16,17] except for the bulky triptycene-bound poly-A. [15] Here, we show that a rationally designed precursor polymer composed of alternating achiral 2,7-linked-fluorene and 2,4-diethynyl-substituted C 2v -symmetric m-phenylene units is quantitatively and chemoselectively converted into a fully π-conjugated ladder polymer with a spiral geometry through the acid-promoted annulative π-extension (Figure 1b).…”