Thermo- and Solvent-Responsive Polymer Complex Created from Supramolecular Complexation between a Helix-Forming Polysaccharide and a Cationic Polythiophene

Abstract

The helical structure is one of key structural components for both biological systems and artificial chiral systems. So far, we have succeeded in fabricating "tight" insulated molecular wires consisting of a triple-stranded cohelical structure formed through supramolecular wrapping of synthetic polymers by a helix-forming polysaccharide (schizophyllan). Herein, we have designed a new modified polysaccharide (Cur-oeg) to form a "loose" macromolecular complex with a conjugated polymer (CP) that allows structural changes in response to external stimuli. Cur-oeg forms a helical complex with an achiral cationic polythiophene (PT1), and the effective conjugation length is changed by temperature, showing a large absorption peak shift from 403 to 482 nm between 85 and 5 °C. According to the change in the conjugation system, the fluorescence and the induced circular dichroism show the continuous spectral shifts under temperature control. The color changes in the absorption and the fluorescence are detectable with observation by the naked eye and are reversibly controlled under thermal cycles, indicating that this system has the function of a "molecular thermometer". It is shown that the induced thermoresponsiveness is associated with structural rearrangement of the helical conformation of PT1 in the complex. Moreover, another unique responsiveness is discovered for the film state: that is, the film color is varied when it is exposed to the vapor of water or methanol (vaporchromism), resulting from the structural change of PT1 occurring even in the film state. These flexible molecular motions in both the solution state and the film state can be applicable to the design of CP-based smart sensors, polarized materials, switching devices, etc.

Thermometry at the nanoscale

“…Other thermometers are based on the temperature dependence of an intensity ratio (the ratiometric thermometers listed above), and on the change of the wavelength at which absorption 132,146 or fluorescence 136 is maximum. The ratiometric thermometer reported by Pietsch et al 77 uses the excimers-to-monomers emission intensity ratio of pyrene.…”

Microfibers from interpolymer complexation of κ-carrageenan and oligomers of polyaniline for glucose detection

“…In those complexes, conductive polymers are considered in the hydrophobic cavity formed by the polysaccharide helix. In another complex of PEGylated curdlan and cationic polythiophene, the supramolecular complexation occurs between the strand of polysaccharide and the chiral conductive polymers [17]. In our work, the PANI is template polymerized in the presence of polyanion, growing in the vicinity of sulfonic acid groups, resulting in a product of non-stoichiometric interpolyelectrolyte complex or interpolymer complex [18].…”

Helically assembledπ-conjugated polymers with circularly polarized luminescence

“…On the other hand, an analogous P15 complex with a polysaccharide, Curdlan derivative (Cur-oeg, see scheme 7), has been found to exhibit reversible color changes in response to thermal stimuli and exposure to solvent [79]. Cur-oeg is a β -1,3-glucan and can form the supramolecular helical nanowire complex with achiral P15 in the same manner as SPG.…”