Fluorescent Mesostructured Polythiophene–Silica Composite Particles Synthesized by in Situ Polymerization of Structure-Directing Monomers

Abstract

Strongly fluorescent micrometer-sized mesostructured polythiophene–silica composite particles were synthesized, and their absorption and fluorescence properties were found to be dependent on their mesostructures. Two cationic trimethylammonium bromide surfactants carrying a thiophene group at the end of their hydrophobic tail were prepared to serve as both structure-directing agents and monomers. The synthesis using the surfactant with a 10-carbon chain in between the thiophene group and the positively charged headgroup under acidic conditions produced spherical particles with a wormlike mesostructure, and that using the surfactant with a 12-carbon chain yielded particles with curved morphologies and a two-dimensional hexagonal mesostructure. In situ polymerization of the thiophene groups closely packed in the central region of the nanoscale silica pore channels resulted in mesostructured polythiophene–silica composite particles. The absorption and fluorescence emission of the composite particles directed by the longer tail surfactant were found to be red-shifted relative to those of the particles directed by the shorter tail surfactant. This red shift was ascribed to the larger effective conjugation length of the polythiophene chains confined in the pore channels of the hexagonal mesostructure compared to that in the pore channels of the wormlike mesostructure.