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-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 ¹H 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 λ_max of the π→ π* 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.