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

Abstract

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.