Synthesis and chemosensory application of water-soluble polyfluorenes containing carboxylated groups

Detection of metal ions in aqueous solutions is a major issue for environmental protection. Conjugated polyelectrolytes showing high sensitivity and selectivity towards the detection of metal ions are highly desirable. We report a water-soluble polyfluorene containing carboxylated groups (P1), poly[9,9′-bis(3′′-propanoate)fluoren-2,7-yl] sodium salt, which shows high recognition capability toward Cu⁺ and Cu ²⁺. P1 was prepared via the hydrolysis of poly[9,9′-bis(tert- butyl-3′′-propanoate)fluoren-2,7-yl] (P0) which was synthesized by Suzuki coupling polymerization. The photoluminescence (PL) spectra of P1 in aqueous solution are significantly quenched in the presence of Cu⁺ and Cu²⁺. P1 shows high selectivity and sensitivity toward Cu ⁺ and Cu²⁺, with the Stern-Volmer constants (K _sv) being 3.5 × 10⁶ and 5.78 × 10⁶ M^-1, respectively. Moreover, the stoichiometric ratio of the P1 repeat unit to Cu⁺ or Cu²⁺ is 2 : 1 obtained from Job's plot. P1 maintains high selectivity towards Cu⁺ or Cu²⁺ in the presence of various metal cations. Our results demonstrate that P1 shows very high sensitivity and selectivity in recognizing Cu⁺ and Cu ²⁺, indicating that it is a promising functional material for chemical sensors.