Aggregation-Driven Growth of Size-Tunable Organic Nanoparticles Using Electronically Altered Conjugated Polymers

A novel class of monodisperse conjugated polymer nanoparticles have been readily prepared
by the facile reprecipitation of poly{1,3-bis[2-(3-alkylthienyl)]azulene} or poly{1,3-bis[2-(3-alkoxythienyl)]azulene}. The multicomponent poly(bithiophene-alt-azulene) macromolecules were efficiently self-assembled
into a wide range of size-tunable nanoparticles from a few tens to five hundred nanometers via the
hydrophobic and π-stacking effects in the mixed chloroform/methanol solutions. Electronically altered polymer
structures with different alkyl or alkoxy substitutes exhibited variable self-assembling behaviors to precisely
tune the size and the optical/electronic properties of nanoparticles. A strong size dependence of continuous
bathochromic absorption and significant enhanced emission were observed with the increase of particle
size. A linear relationship between the absorption or fluorescence intensities and the particle size was
demonstrated as well, and this is very useful to probe the intermolecular interactions and the size evolutions
of conjugated polymer nanoparticles. After the size-dependent optical and electronic properties are created,
they can be further optimized to improve the performance of materials prior to the use in novel organic
nanodevices in a cost-effective way.