A branched 2,2′-biimidazole-based polymer with multiple sensing properties

• New branched conjugated polymer possesses multifunctional sensing properties to Co2+, Ag+, cysteine and strong acidic gas.
• The linear range of detection for cysteine is easily tuned by adding different concentration of Ag+ ions.
• Low detection limit was achieved for HCl gas with fast response rate.
• Compared with the linear polymer, the branched polymer possesses higher sensitivity.

Herein, new linear and branched conjugated polymers containing 2,2′-biimidazole moiety were successfully designed and synthesized through Suzuki coupling reactions, and their fluorescence sensing properties to metal ions, amino acids, and acid gas were investigated. The emission of the two polymers can be efficiently quenched by Co2+ through a photo-induced electron transfer process with “turn off” character without disturbance of Cu2+. The polymers also show ratiometric fluorescence changes toward Ag+, and the resulting polymer–Ag+ complexes exhibit excellent sensing properties for detection of cysteine with high selectivity and fast response (less than 1 min). The linear detection range of cysteine can be tuned conveniently by changing the amount of Ag+ ions. In addition, we also found that the emission color of the polymer solution can reversibly change from blue to green on exposure to HCl and NH3 gases, which may be utilized to detect strong acidic gas efficiently. All the results demonstrate that the 2,2′-biimidazole-based conjugated polymers can be used as excellent multifunctional fluorescent sensors. It should be noted that the branched polymer possesses a higher sensitivity, compared with the linear polymer.

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