| By increasing the structural similarity between the trigger and the applied liquid crystal, it was found that the twisting power of [3.2.1]bicycloketone derivative 4 has been improved up to 7.5 times higher than that of [3.2.1]bicyclooctan-3-one 2 in the applied liquid crystal PCH1115. This improvement leads to the development of chiroptical liquid crystal switch with greater potential for the application.;By incorporating the bicycloketone chromophore into the helical polyisocyanate backbone, a model system has been created, subject to quantitative interpretation with statistical physical ideas, in which chiral information inherent in circularly polarized light can be used to control the helical characteristics of a polymer. For this purpose, the racemic bicycloketone chromophore was pended through different linkage patterns to the helical polyisocyanate backbone with dynamically interconverting equal populations of left and right handed helical backbone conformations. Irradiation with circularly polarized light in the chromophore of the chiral pendant gave rise to easily measurable circular dichroism signals of the helical amide backbone of the polyisocyanate, which changed sign with change in the sense of the circularly polarized light. This demonstrated that the minute enantiomeric excess produced by the irradiation was capable of being transferred to the polyisocyanate backbone, leading to one handed helical sense of the polymer chain becoming predominant over the other. The results, expressed as the optical activity as a function of the degree of polymerization, could be analyzed using an approximate solution of a one-dimensional quenched random field Ising model. The experimental data were perfectly fit to the theory, allowing determination of the chiral-bias-magnitude controlled crossover between "statistical and thermal randomness". |
