Preparation of nano‐ and microparticles through self‐assembly of azobenzene‐pendent ionomers

Abstract

ABSTRACT:The particle formation of azobenzene-containing ionomers, through self-assembly, in aqueous media (THF/H 2 O solvent) was studied. The ionomers were synthesized by copolymerization between azobenzene-pendent methacrylate and methacrylic acid. It was revealed by UVvis spectra and light scattering measurements that the extent of H-aggregation of the azobenzene units first decreased, and then increased with increasing volume fraction of H 2 O of the solvent. The H 2 O fraction at which the extent of H-aggregation began to increase became lower, when the copolymers contained more azobenzene units. Colloidal particles were prepared by slow addition of various concentrations of aqueous NaOH to the copolymer THF solutions. The hydrodynamic diameters of the particles obtained by the procedures were several hundreds of nanometer. When the azobenzene unit content in the copolymer was smaller, the diameters of the particles became smaller. When the colloidal particles dispersions were cast on a carbon sheet and dried, the particles aggregated and formed larger spherical particles, with diameters of several micrometers. The size of the particles obtained by the drying process became smaller, when higher concentrations of aqueous NaOH solutions were used. Therefore, the particle sizes were controlled by the azobenzene units content in the copolymers and the concentration of aqueous NaOH solutions.

Synthesis and Photophysical Properties of Nonbenzoid Ended Fluorophores

“…In contrast to fluorescence decrement, absorption spectra of 23 showed hypsochromic shift as the water fraction increased (Figure ). This might be assigned to H -aggregation, which is consistent with many other spectroscopic findings. − We postulate that the less steric ending group in 23 allowed for the central fluoroene rings in adjacent molecules to achieve cofacial stacking and resulted in a planarization of the π-system, which lead to strong intermolecular attraction in the solid state and resulted in decreased emission efficiency in nanoparticles.

5 Emission Efficiency Tuned by Different Centers and Ending Groups

6 Emission Efficiency Tuned by Different Length of Side Chains

7 Absorption (left) and emission spectra (right) of 11 in varied water/THF mixture.

8 Up: (left) The single molecule structure of 11 ; (right) the single molecule structure of 17 optimized at the PM3 theory.

…”

“…This might be assigned to H-aggregation, which is consistent with many other spectroscopic findings. [30][31][32] We postulate that the less steric ending group in 23 allowed for the central fluoroene rings in adjacent molecules to achieve cofacial stacking and resulted in a planarization of the π-system, which lead to strong intermolecular attraction in the solid state and resulted in decreased emission efficiency in nanoparticles.…”

Photo-driven smart polymers and their molecular self-assembly

“…shift happens. H-aggregates have been reported by many researchers to have formed in azobenzene amphiphiles and polymers both in aqueous solution 182 and in aggregation form, e.g., micelles, 154 vesicles, 183 bilayers 184 or membranes. 185 By contrast, if the transition dipoles are in line (rather than parallel), the spectra exhibited a bathochromic (red) shift and the aggregates are, in this case, termed as J-aggregates.…”