Synthesis and luminescent properties of poly(phenylene-ethynylene- carbazole)s with aniline as side-groups

The poly(phenylene-ethynylene-carbazole) (PPEC) with 4-vinylaniline pendant groups was synthesized through Pd-catalyzed Sonogashira coupling polymerization between 4-[2-(2, 5-dibromophenyl) vinyl] aniline (M1),1,4-di-2,5-bis(pentyloxy) (M2) and 3,6-dibromo-9-octylcarbazole (M3). The ratio of aniline unit to ethynyl-benzene unit to carbazole unit at 0. 54:1:0. 46 was determined by H NMR spectrum. When PPEC is aggregated by adding nonsolvents such as water,methanol and hexane into its THF solution,the fluorescence intensity and the maximum emission peak of PPEC changed drastically. The fluorescence intensity gradually decreased upon addition of water into PPEC THF solution before the ratio of THF to water arrived at 50:50. The fluorescent intensity of PPEC increased in turn after water fraction is beyond 60% in the mixture of THF and water. When methanol was added into its THF solution,however,PPEC showed an aggregation-caused quenching (ACQ) characteristic. The emission of PPEC is only enhanced by aggregation when adding n-hexane into its THF solutions, exhibiting an aggregation-induced emission enhancement (AIEE) effect. The result indicates that amino groups can strengthen the inter-chain and intra-chain interactions in PPEC and restrict the non-radiative energy transition. This strategy thus provides a new concept for designing highly emissive conjugated polymers by adjusting side-group interaction.