N-Arylated bisferrocene pyrazole for the dual-mode detection of hydrogen peroxide: an AIE-active fluorescent "turn ON/OFF" and electrochemical non-enzymatic sensor

A series of new N-arylated bisferrocene pyrazole (D-p-A-p-D) chromophores have been synthesized by the Chan-Lam cross-coupling (1, 2) and Buchwald-Hartwig amination (3, 4) reactions. The compounds 1-4 were characterized using analytical and spectroscopic methods. Compounds 1 and 3 showed positive solvatochromism and later, compounds 2 and 4 exhibited negative solvatochromism. The compounds 1-4 interestingly exhibited highly enhanced fluorescence intensity in their aggregate states, while in the solution states, they exhibited low fluorescence intensity. The origin of enhanced emission in the aggregated state was due to the restriction of intramolecular rotation, especially in the mixture having a ratio of 40 : 60 (CH3CN/H2O). The aggregation-induced emission (AIE) properties were utilized to detect H2O2, which showed a quick response in a linear range of 10-50 mM with detection limits of 38.8 nM (1) and 15.9 nM (3). Furthermore, the electrochemical reduction of hydrogen peroxide in the same linear range as above showed limits of detection (3s) of 14.4 mM (1) and 11.6 mM (3).