AIEE active sensors for fluorescence enhancement based detection of Ni2+ in living cells: Mechanofluorochromic and photochromic properties with reversible sensing of acid and base.

ABSTRACT

Stimuli responsive sensors QI 1 and QI 2 were rationally developed which exhibited diverse features of mutable mechanofluorochromism, reversible photochromism, solvatochromism, aggregation induced emission enhancement (AIEE), and metal ion sensing. After observing the exceptional structural property relationship, sensors were applied for reversible colorimetric and fluorometric determination of Ni2+ with low detection limits of 12 and 17 nM, respectively. Fluorescence emission enhancement based Ni2+ sensing was induced by chelation enhanced fluorescence (CHEF) mechanism. CHEF is triggered by the inhibition of excited state intramolecular proton transfer (ESIPT) and -C=N isomerization. The proposed Ni2+ sensing mechanism was investigated through 1H NMR, FT-IR titration, theoretical studies, and Jobs plots. Further, the developed sensors successfully demonstrated the selective acid-base induced absorption/emission switching through reversible ring-opening/closing and keto-enol tautomerization, evidenced by 1H NMR titration experiments. Additionally, the sensitivity of the sensor QI 1 towards Ni2+ was effectively mimicked in live MCF-7 cells and industrial effluents. Furthermore, monitoring of Ni2+ ions was also accessed through inexpensive and portable sensors' coated fluorescent films. Finally, an INHIBIT logic gate was fabricated imputing Ni2+ and EDTA as input signals to electronically scrutinize the targeted Ni2+.