Tunable fluorescence upon aggregation: Photophysical properties of cationic conjugated polyelectrolytes containing AIE and ACQ units and their use in the dual-channel quantification of heparin

A series of cationic conjugated polyelectrolytes named as PTPE _xF_yN, which consist of tetraphenylethylene (TPE) as aggregation-induced emission (AIE) units and fluorene (F) as aggregation-caused quenching (ACQ) units, have been synthesized by the quaternization of the corresponding neutral polymers. These cationic conjugated polyelectrolytes exhibited aggregation-induced emission enhancement (AIEE) and dual-channel fluorescence response (DCFR) when aggregated in solution, either by adding non-solvent or by adding heparin. The fluorescence intensity of PTPEN or PTPE_0.5F_0.5N in the fluorescence titration curves showed a linear increasing relationship with the concentration of heparin, while the fluorescence intensity of PTPE_0.3F_0.7N, PTPE _0.2F_0.8N and PTPE_0.1F_0.9N showed DCFR (i.e., two independent linear relationships) with the concentration of heparin, one attributed to the ACQ signal and the other attributed to the AIEE signal. The mechanism of AIEE was investigated by calculating the radiative and nonradiative decay rate constants using the experimental data of photoluminescence (PL) quantum yields and lifetimes of PTPE_xF _yN in solution and aggregation state. At last, the successful quantification of heparin by the PTPE_0.2F_0.8N solution was demonstrated, which showed good linearity and sensitivity.