Photoresponsive soft materials: Synthesis and photophysical studies of a stilbene-based diblock copolymer

Abstract

An amphiphilic diblock copolymer composed of a photoresponsive dialkoxycyanostilbene polymethacrylate and poly(ethylene oxide) (PDACS-b-PEO) was synthesized and its photophysical and aggregation properties were investigated. The amphiphilic nature of the polymer caused it to self-assemble in water, and dynamic light scattering studies indicated formation of spherical aggregates with an average size of 160 nm. Atomic force microscopy images of dried films cast from solutions containing the polymer aggregates revealed supramolecular aggregates with a spherical morphology. Photoisomerization of the stilbene chromophore in PDACS-b-PEO on UV irradiation resulted in the destruction of the self-assembled superstructures which could be attributed both to change in shape of the chromophore from the linear trans isomer to the bent cis isomer which would hinder self-aggregation of the molecules and the higher dipole moment of the cis isomer leading to a reduction of the hydrophobic nature of the stilbene containing block of PDACS-b-PEO. It was observed that hydrophobic dyes such as curcumin could be encapsulated within the hydrophobic interior of the spherical micellar aggregates from which the encapsulated dye could be released on UV irradiation.