Water soluble photo- and electroluminescent alkoxy-sulfonated poly(p-phenylenes) synthesized via palladium catalysis

Water soluble poly(p-phenylene) derivatives, poly[2,5-bis(3-sulfonatopropoxy)-1,6-phenylene-abt-1,4-phenylene] sodium salt (PPP-OPSO3) and poly[2,5-bis(3-sulfonatopropoxy)-1,4-phenylene-alt-4,4'-biphenylene] sodium salt (PPBP-OPSO3), have been synthesized through a Suzuki coupling reaction of 1,4-dibromo-2,5-bis(3-sulfonatopropoxy)benzene sodium salt with 1,4-phenylenediboronic acid or 4,4'-biphenyldiyldiboronic acid 2,2'-dimethylpropyl diester using a water soluble Pd(0) catalyst or Pd(OAc)(2). The pH dependence of the coupling reaction was investigated and resulted in pH independence at pH levels greater than 10.0. End group analysis of PPP-OPSO3 via H-1 NMR of tert-butyl end-capped polymers indicates degrees of polymerization in excess of 40 (ca. 80 rings per chain). Viscometric analysis of PPP-OPSO3 in water shows a behavior comparable to sodium poly(styrenesulfonate) !PSS) of molecular weight 8000. In addition, the polyelectrolyte effect is observed at low polymer concentrations. The lambda(max) of the pi --> pi* absorption for PPP-OPSO3 is found at 339-342 nm, while that of PPBP-OPSO3 shows a bathochromic shift to 349-352 nm. All of the water soluble PPP oligomers and polymers feature strong blue fluorescence. The fluorescence has been characterized by quantum yield and lifetime studies. Nanosecond-microsecond laser flash photolysis experiments indicate that direct excitation of the polymers in the near-UV leads to triplet state formation, albeit with comparatively low efficiency. Multilayered films of PPP-OPSO3 were fabricated with poly(ethyleneimine) (PEI) using layer-by-layer self-assembly and incorporated into blue-light-emitting devices.