Host–guest complexation‐triggered chiroptical change of poly(phenylacetylene)s bearing binaphthocrown ether moieties on the main chain

Abstract

Diacetylene monomers with respective lengths of the oxyethylene chains were cyclopolymerized with a rhodium catalyst to produce novel poly(phenylacetylene)s bearing a different cavity size of the chiral crown ether in the repeating units (2a-c). In the circular dichroism spectra of the resulting polymers, characteristic Cotton effects were observed in the range from 350 to 500 nm corresponding to the absorption of the conjugated polymer backbone, indicating that the polymers possessed a helical structure with an excess single screw sense induced by the covalently bonded binaphthyl units. The host-guest complexation of 2a-c with achiral guests produced a chiroptical change based on the fluctuation in the main chain conformation. The behavior of the complexation-induced chiroptical change was essentially dictated by the cavity size of the binaphthocrown ether units. Additionally, a chiralityresponsive helicity change was observed in the case of the complexation of 2a-c with chiral guests, which also depended on the crown ether size.

Cyclopolymerizations: Synthetic Tools for the Precision Synthesis of Macromolecular Architectures

“…Polymers with 29−41 membered crown cavities containing chiral binaphthyl groups were synthesized by the cyclo-polymerization of the corresponding bis(ethynylbenzene)s (169) catalyzed by Rh(nbd)BPh 4 (Figure 63). 325 The cyclopolymerization was performed in highly diluted conditions ([monomer] = 0.02 mol L −1 ) in order to obtain gel-free polymer. CD analysis of the polymers confirmed their helical structures with an excess single screw sense, which is induced by the chiral binaphthyl units.…”

Multicyclic Polymer Synthesis through Controlled/Living Cyclopolymerization of α,ω-Dinorbornenyl-Functionalized Macromonomers

“…This strategy, however, is exceedingly challenging since the cyclization reaction of long linear precursors to form large rings is thermodynamically disfavored. Indeed, typical cyclopolymerizations provide thermodynamically stable five- or six-membered rings, − and a 37-membered ring is the ring-size record for cyclic repeating units prepared so far by cyclopolymerization. The root cause of this issue involves the interplay between the monomer concentration and the polymerization kinetics.…”

Recent progress on using BINOLs in enantioselective molecular recognition

“…Polymers (R)-73b and (R)-73c also displayed chiral recognition ability for phenylglycine perchlorate. 82 Mixing a chiral amine, (R)-BINOL and o-formyl phenyl boronic acid (FPBA) leads to efficient formation of the three component assembly product (R)-74, which produces CD signals for each enantiomer of the amine (Fig. 32).…”