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)-1,4-phenylene- alt -1,4-phenylene] sodium salt (PPP−OPSO 3 ) and poly[2,5-bis(3-sulfonatopropoxy)-1,4-phenylene- alt -4,4‘-biphenylene] sodium salt (PPBP−OPSO 3 ), 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−OPSO 3 via 1 H NMR of tert -butyl end-capped polymers indicates degrees of polymerization in excess of 40 (ca. 80 rings per chain). Viscometric analysis of PPP−OPSO 3 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 λ max of the π → π* absorption for PPP−OPSO 3 is found at 339−342 nm, while that of PPBP−OPSO 3 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−OPSO 3 were fabricated with poly(ethyleneimine) (PEI) using layer-by-layer self-assembly and incorporated into blue-light-emitting devices.