Temperature-Regulated Fluorescence and Association of an Oligo(ethyleneglycol)methacrylate-Based Copolymer with a Conjugated Polyelectrolyte—The Effect of Solution Ionic Strength

Abstract

Aqueous mixtures of a dye-labeled non-ionic thermoresponsive copolymer and a conjugated cationic polyelectrolyte are shown to exhibit characteristic changes in fluorescence properties in response to temperature and to the presence of salts, enabling a double-stimuli responsiveness. In such mixtures at room temperature, i.e., well below the lower critical solution temperature (LCST), the emission of the dye is strongly quenched due to energy transfer to the polycation, pointing to supramolecular interactions between the two macromolecules. Increasing the concentration of salts weakens the interpolymer interactions, the extent of which is simultaneously monitored from the change in the relative emission intensity of the components. When the mixture is heated above its LCST, the transfer efficiency is significantly reduced, signaling a structural reorganization process, however, surprisingly only if the mixture contains salt ions. To elucidate the reasons behind such thermo- and ion-sensitive fluorescence characteristics, we investigate the effect of salts of alkali chlorides, in particular of NaCl, on the association behavior of these macromolecules before and after the polymer phase transition by a combination of UV-vis, fluorescence, and (1)H NMR spectroscopy with light scattering and small-angle neutron scattering measurements.

Effects of architecture on the stability of thermosensitive unimolecular micelles

“…Fluorescence spectroscopy is a powerful method to learn about intermolecular aggregation and micellization. 43 We used two different dyes, whose emission spectra are sensitive to the polarity of the surrounding medium, in order to detect the presence of hydrophobic domains: pyrene and 4-(dicyanomethylene)-2-methyl-6-( p-dimethylaminostyryl)-4H-pyran (abbreviated here as 4HP; another abbreviation is DCM). 20 Pyrene is a prominent standard probe by taking the intensity ratio I 1 /I 3 of the first and third vibronic emission bands.…”

Stimuli-Responsive Polymers Providing New Opportunities for Various Applications

“…Response to ionic strength is typical property of some neutral and ionisable polymers. Changes in ionic strength can cause changes in the size of polymeric structures or nanoaggregates, swelling-shrinkage of gels, solubility of polymers, and fluorescent quenching kinetics of chromophores of polyelectrolytes [176][177][178][179][180][181]. Salt added to solutions of anionic and cationic polymers increases electrostatic interactions among groups in polymer chains [181].…”

Cationic Main‐Chain Polyelectrolytes with Pyridinium‐Based p‐Phenylenevinylene Units and Their Aggregation‐Induced Gelation

“…Side‐ or main‐chain polyelectrolytes that contain charged, π‐conjugated repeat units are an interesting class of materials for potential applications in chemo‐ or biosensing as well as optoelectronic devices such as solar cells or organic light emitting diodes . In recent years, side‐chain conjugated polyelectrolytes based on several backbone motifs were developed including polyfluorenes, fluorene–benzothiazole copolymers, polythiophenes, poly‐ p ‐phenylenevinylenes, poly‐ p ‐phenyleneethynylenes among others for applications in sensing, imaging, as well as for enzyme activity, and charge transport studies . Fully conjugated poly(pyridinium salt)s, or polyelectrolytes containing viologen, as well as diethynylpyridinium units as main‐chain polyelectrolytes have been synthesized mainly for biosensing and optoelectronic applications.…”