Synthesis of Organic and Water Soluble Poly(1,4-phenylenevinylenes) Containing Carboxyl Groups: Living Ring-Opening Metathesis Polymerization (ROMP) of 2,3-Dicarboxybarrelenes

2,3-Dicarboxybicyclo[2.2.2]octa-2,5,7-triene (barrelene) monomers ( 4a,b ) were synthesized by a novel route and then polymerized by ring-opening metathesis polymerization (ROMP). Complete initiation of the ROMP initiator ( 5 ) and living polymerization of monomer 4b were achieved by tuning the activity of 5 with hexafluoro- tert -butanol (HFB) and tetrahydrofuran (THF). The precursor polymers ( 6a,b ) were readily converted to diester-substituted poly(1,4-phenylenevinylenes) (PPVs) ( 7a,b ) by aromatizing the cyclohexadiene rings using 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). The resulting PPVs were highly luminescent, and polymer 7b, bearing tert -butyl groups on its esters, was soluble in methylene chloride and chloroform. We found that partially oxidizing 6b so that only 80% of the polymer units are aromatized increases both the solubility and photoluminescence quantum yield of 7b . Deprotection of polymer 7b by acid-catalyzed thermolysis of the tert -butyl groups followed by treatment with aqueous base produced a dicarboxylate PPV ( 9 ) that is soluble in water. Photoluminescence and UV/visible absorbance measurements show that, in solution, the PPVs synthesized are highly luminescent and blue shifted relative to films of unsubstituted PPV.