Stimuli-responsive block copolymers as pH chemosensors by fluorescence emission intensification mechanism

Abstract

Stimuli-responsive block copolymers containing light-responsive coumarin moieties were synthesized using 7-(2-bromoisobutyryloxy)-4-methylcoumarin as an initiator of atom transfer radical polymerization. The resulted smart block copolymers, poly(7-acryloyloxy 4-methylcoumarin-r-methyl methacrylate)-b-poly(dimethylaminoethyl methacrylate) (P(CMA-r-MMA)-b-PDMAEMA) and poly(7-acryloyloxy 4-methylcoumarin)-b-poly(dimethylaminoethyl methacrylate) (PCMA-b-PDMAEMA), were used for pH detection by aggregation-induced fluorescence emission intensification mechanism. Calculation of hydrophilic fraction of the block copolymers by nuclear magnetic resonance spectroscopy proved micellar structure of self-assembled copolymer chains in aqueous media. Dimerization kinetics of the coumarin moieties in the micellar assemblies was investigated by ultraviolet–visible spectroscopy at different pH values. The resulted aqueous micellar dispersions of the block copolymers with different compositions were utilized for pH detection by using fluorescence spectroscopy. The copolymer containing MMA units as a spacer between coumarin moieties (P(CMA-r-MMA)-b-PDMAEMA) showed higher dimerization kinetics and applicability as a fluorescence chemosensor for detection of pH. By contraction of PDMAEMA blocks at higher pH values and consequent aggregation state of the coumarin moieties in the core, the change of fluorescence intensity was used for fluorescence sensation of pH.