Tunable fluorescence conjugated copolymers consisting of tetraphenylethylene and fluorene units: From aggregation-induced emission enhancement to dual-channel fluorescence response

A series of new conjugated polymers PTPE_xF_y, which consist of tetraphenylethylene (TPE) units and fluorene (F) units, have been designed and synthesized by Suzuki cross-coupling polymerization. The polymers PTPE_xF_y exhibited aggregation-induced emission enhancement and dual-channel fluorescence response (DCFR) when they were aggregated in solution, and these properties are related with their TPE-to-F ratio in the polymer backbone. For PTPE and PTPE_0.5F_0.5, the fluorescence emission was enhanced by aggregation when water was added into their THF solutions. For the copolymers PTPE_0.3F_0.7, PTPE_0.2F_0.8, and PTPE_0.1F_0.9, the DCFRs were observed when they were aggregated by adding water into their solution, which can be attributed to the different responses of fluorene segments and TPE segments to aggregation. The fluorene segments have an aggregation-caused quenching characteristic, whereas the TPE segments have an aggregation-induced emission characteristic. According to the fluorescence lifetime and quantum yield data of the polymer solutions, we have discovered that the polymer's natural life time increases as its TPE content increases. In the solid film, PTPE_0.3F_0.7 and PTPE_0.2F _0.8 showed better quantum yield than other polymers, due to the combination of the excellent fluorescent property of the fluorene groups and the nonplanar conformation of the TPE groups.