Ultra‐fast One‐Handed Helix Induction and Its Static Helicity Memory in a Poly(biphenylylacetylene) with a Catalytic Amount of Chiral Ammonium Salts

Abstract

AbstractWe report an ultra‐fast helix induction and subsequent static helicity memory in poly(biphenylylacetylene) (PBPA‐A) assisted by a catalytic amount of nonracemic ammonium salts comprised of non‐coordinating tetrakis[3,5‐bis(trifluoromethyl)phenyl]borate (BArF−) as a counter anion. The remarkable acceleration of the helix‐induction rate in PBPA‐A accompanied by the significant amplification of the asymmetry relies on the two methoxymethoxy groups of the biphenyl pendants, which can gain access to enfold the chiral ammoniums in a crown‐ether manner in specific aromatic solvents, leading to ultra‐fast helicity induction, which is completed within 30 s. In aromatic solvents, helicity memory is lost rapidly, but is quite stable in long‐chain hydrocarbons. The best use of specific solvents for helicity induction and static helicity memory, respectively, provides a highly sensitive chirality sensing system toward a small amount of chiral amines and amino acids when complexed with BArF−.