Abstract
Helical nanostructures have attracted continuous attention, not only as media for chiral recognition and synthesis, but also as motifs for studying intriguing physical phenomena that never occur in centrosymmetric systems. To improve the quality of signals from these phenomena, which is a key issue for their further exploration, the most straightforward is the macroscopic orientation of helices. Here as a versatile scaffold to rationally construct this hardly accessible structure, we report a polymer framework with helical pores that unidirectionally orient over a large area (∼10 cm2). The framework, prepared by crosslinking a supramolecular liquid crystal preorganized in a magnetic field, is chemically robust, functionalized with carboxyl groups and capable of incorporating various basic or cationic guest molecules. When a nonlinear optical chromophore is incorporated in the framework, the resultant complex displays a markedly efficient nonlinear optical output, owing to the coherence of signals ensured by the macroscopically oriented helical structure.
Highlights
Helical nanostructures have attracted continuous attention, as media for chiral recognition and synthesis, and as motifs for studying intriguing physical phenomena that never occur in centrosymmetric systems
With the aim of developing such frameworks, we focused on an advanced version of molecularly imprinted polymers[23] prepared by the crosslinking of liquid crystals (LCs), which have been pioneered by Gin et al.[24] and are regarded as a new class of solid-state hosts[25,26,27,28,29,30,31,32]
When a multicomponent LC composed of a polymerizable frame unit and a non-polymerizable template unit is in situ crosslinked, the frame units are converted into a polymer framework, while the template units are noncovalently captured in the polymer framework and are exchangeable with other molecules
Summary
Helical nanostructures have attracted continuous attention, as media for chiral recognition and synthesis, and as motifs for studying intriguing physical phenomena that never occur in centrosymmetric systems. We report an unprecedented type of polymer framework with macroscopically oriented helical pores, prepared by in situ crosslinking of a supramolecular LC preorganized in a magnetic field This achievement results from our unexpected finding that a chiral liquid crystalline salt we recently developed[27,28] meets all requirements as the precursor of such framework, that is, multicomponent nature, polymerizability[24,25,26,27,28,29,30,31,32], orientability[18,19,20,21,22,31,32,33,34,35,36,37,38,39,40] and helicity with controlled handedness[11,12,13,14,15,16,17]. The resultant polymer framework serves as a versatile scaffold for arraying various molecules in a macroscopically oriented helical structure, thereby offering useful motifs for the exploration of the physical phenomena particular to noncentrosymmetric systems
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