Chirality Construction from Preferred π-π Stacks of Achiral Azobenzene Units in Polymer: Chiral Induction, Transfer and Memory

Abstract

Abstract:The induction of supramolecular chirality from achiral polymers has been widely investigated in composite systems consisting of a chiral guest, achiral host, and solvents. To further study and understand the process of chirality transfer from a chiral solvent or chiral molecules to an achiral polymer backbone or side-chain units, an alternative is to reduce the components in the supramolecular assembled systems. Herein, achiral side-chain azobenzene (Azo)-containing polymers, poly(6-[4-(4-methoxyphenylazo) phenoxy] hexyl methacrylate) (PAzoMA), with different M n s, were synthesized by atom transfer radical polymerization (ATRP). Preferred chirality from supramolecular assembled trans-Azo units of PAzoMAs is successfully induced solely by the neat limonene. These aggregates of the polymers in limonene solution were characterized by circular dichroism (CD), UV-vis spectra, and dynamic light scattering (DLS) under different temperatures. The temperature plays an important role in the course of chiral induction. Meanwhile, supramolecular chirality can be constructed in the solid films of the achiral side-chain Azo-containing polymers that were triggered by limonene vapors. Also, it can be erased after heated above the glass transition temperature (T g ) of the polymer, and recovered after cooling down in the limonene vapors. A chiroptical switch can be built by alternately changing the temperature. The solid films show good chiral memory behaviors. The current results will facilitate studying the mechanism of chirality transfer induced by chiral solvent and improve potential application possibilities in chiral film materials.

Light-triggered thermal conductivity switching in azobenzene polymers

“…(The trans-azopolymer melting point is 80°C.) Previous studies of polymers with similar azobenzene side-chain structures in trans states have reported glass-transition temperatures in the range of 35 < T g < 80°C (29)(30)(31). We note that similar large shifts in T g as a function of isomer state have been previously observed in polybutadiene (ΔT g ∼ 90°C) (32) and azobenzene functionalized polymers (ΔT g ∼ 60°C) (21).…”

Supramolecular Chirality in Azobenzene-Containing Polymer System: Traditional Postpolymerization Self-Assembly Versus In Situ Supramolecular Self-Assembly Strategy

“…Furthermore, the chirality of Azo-polymers can be disrupted by UV light irradiation, and dynamically recovered by visible light irradiation or temperature regulation owing to the reversible trans - cis - trans isomerization. Thus, the chiral-achiral chiroptical switches can be achieved based on the reversible trans - cis isomerization of Azo building blocks [ 137 ]. In this section, we will mainly discuss the construction of chirality in the side-chain photochromic Azo-polymers by postpolymerization self-assembly.…”

“…The results of CD and UV-vis spectra suggested that the internal structures and external stimuli have distinctive influences on the induction and regulation of supramolecular chirality of achiral Azo-polymers. Recently, we used the same Azo-polymer 20 and successfully yielded CD-active Azo-polymer films triggered by chiral limonene vapor [ 137 ]. Chiroptical induction, switching, memory of the polymer films were systematically studied.…”

Aggregation-induced chiroptical generation and photoinduced switching of achiral azobenzene-alt-fluorene copolymer endowed with left- and right-handed helical polysilanes

“…To obtain more versatile and efficient chiral biases, scientists have investigated several chiral stimuli. For example, two types of chiral lights (circularly polarized light due to angular momentum and vortex light due to orbital angular momentum), [7][8][9][10][11][12][13][14][15] chiral nematic liquid crystals and chiral terpenes, [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] chiral molecules with functional groups, 31,32 hydrodynamic swirling ow, 33,34 and biological and articial helical polymers 35 induce supramolecular chirality when achiral and optically inactive molecules and polymers are employed. These driving forces are non-covalent intermolecular weak forces including p-p, C-H/p, C-H/O, C-H/F, cation/p, dipoledipole, and van der Waals (London dispersion) interactions.…”