Control of the Optical Properties of a Star Copolymer with a Hyperbranched Conjugated Polymer Core and Poly(ethylene glycol) Arms by Self-Assembly

A self-assembly approach to tuning the optical properties of a star copolymer is reported herein. The star copolymer HCP-star-PEG with a hyperbranched conjugated polymer (HCP) core and many linear poly(ethylene glycol) (PEG) arms has been prepared successfully. The HCP core was synthesized by Wittig coupling of N-(n-hexyl)-3,6-diformylcarbazole and 1,3,5-bis[(triphenylphosphonio) methyl]benzene tribromide. Subsequently, the linear PEG arms were grafted onto the HCP core by acylhydrazone connection. It was found that the optical properties of HCP-star-PEG in chloroform solution changed on addition of acid. Both H-1 NMR and UV/Vis spectro-scopic investigations confirmed that the variation of the optical properties was related to the complexation of the acid and the imine bond in the acylhydrazone group. HCP-star-PEG self-assembled into core-shell micelles in the mixed solvent of chloroform and acetonitrile, which affected the protonation of the imine bond. Therefore the optical properties of HCP-star-PEG can be readily controlled by self-assembly.