Nanoparticles of Low Optical Band Gap Conjugated Polymers

Sonogashira coupling of 9,9-bis(2-ethylhexyI)- 2,7-diethynyl-9H-fluorene (I) with 2,7-dibromo-9,9-bis(2- ethylhexyl)-9H-fluorene (2) and dibromo-substituted electron accepting arylenes 5,7-bis(5-bromothiophen-2-yl)-2,3- dihexylthieno(3,4-b)pyrazine (3), 4,7-bis(5-bromo-4-(2- ethylhexyl)thiophene-2-yI)bis(benzothiadiazole) (4) or 4,9- bis (5-bromo-4-{2-ethylhexyl)thiophen-2-yl)-6, 7- dihexylthiadiazolo(3,4-g)quinoxaline (5), respectively, in a miniemulsion polymerization process afforded colloidally stable dispersions of poly(arylene ethynylene) nanoparticles with an average size in the range of SO to 120 nm. For these poly((1-alt-(2-co-X)J (X = 3, 4, or 5), poly(l-alt-3), poly(l-alt-4), and poly(l-alt-5) aqueous nanoparticle dispersions absorption occurs increasingly in the red and NIR regime with increasing incorporation of acceptor monomer, with a strong absorption up to Aabs = 1 Jlm for poly(l-alt-4) dispersions. For poly(l-alt-(2- co-3)) nanoparticles fluorescence is also observed at Aem = ca. 700.nm, which occurs at this long wavelength exclUSively even at an incorporation of only 1 mol % of 3 due to energy transfer to the Iow-energy chromophores. An alternative postpolymerization approach by change of solvent quality yielded dilute aqueous dispersions of self-stabilized nanoparticles from. an amphiphilic block copolymer, poly{ethylene glycoI)-block-poly(l-alt-6)-block-poly(ethylene glycol) generated from. alkyne-tenninated poly(l-alt-6) via azide-alkyne coupling (6 = 4,7-bis(5-bromo-4-(2-ethylhexyI)thiophene-2-yl)benzothiadiazole), which fluoresce at Aem mal< = 672 nm.