Quinoline-containing, conjugated poly(aryleneethynylene)s:: Novel metal and H+-responsive materials

We describe the synthesis of novel copolymers containing quinoline, benzene, and alkyne groups by a Pd-catalyzed Heck-Cassar-Sonogashira-Hagihara reaction. Direct iodination of quinoline by a mixture of iodine, potassium periodate, and sulfuric acid in chloroform gives 3,6-diiodoquinoline. 3,6-Diiodoquinoline was coupled to 1,4-diethynyl-2,5-bis(2-ethylhexyl)benzene, and 3,6-diethynylquinoline was coupled to 1,4-diiodo-2,5-bis(2-ethylhexyloxy)benzene. The polymers formed in good-to-excellent yields with a degree of polymerization (P-n) ranging from 11 to 95 and polydispersities (M-w/M-n) from 1.8 to 3.3. Their optical properties (i.e., absorption and emission) were shown to be dramatically dependent upon the presence of protons and to a lesser extent metal cations. The change in fluorescence upon protonation is different for the alkyl- and alkoxy-substituted polymer. In the alkyl case bright yellow fluorescence is observed upon protonation, while for the alkoxy case the polymer's fluorescence is quenched upon addition of acid at polymer concentrations > 0.1 mg L-1.