An Anthracene-Imidazoanthraquinone Conjugate Exhibiting Ratiometric Fluorescence Turn - on Behavior with CN^- and F^- Anions

A new conjugate, 2-(4-(anthracen-9-yl) phenyl)-[1,2-d]imidazole-1H-anthraquninone (AQI) has been designed and synthesized as a molecular probe 4. The photophysical and electrochemical behavior of the probe in the absence and presence of different class of ions were examined in acetonitrile solution. The probe 4 with F^- and CN^- anions showed ratiometric fluorescence "turn - On" response due to variation in ICT processes. Cyclic voltammetry of probe exhibited reversible redox behavior wherein the band gap (E_g =1240/λ_max) of probe (ΔE =3.220 eV) decreased (~2.583 eV) after the interaction with F^- and CN^- anions. The probe interacted with both anions in a 1 : 1 stoichiometry with good binding constants (K_F ^-=.05×10⁶ M^-1 and K_CN ^- = 1.46×10⁶ M^-1) and limit of detection/quantification (LOD/LOQ) in nM range. pH studies showed that probe 4 has potential to detect the anions under physiological conditions (between pH 6-10). The probe upon interaction with both F^- and CN^- anions showed a naked-eye sensitive color change in solution and on test paper strips. The probable complexes, 4+F^-/CN^- upon interaction with trifluoroacetic (TFA) acid showed reversible behavior wherein the intensity of probe rejuvenated. The output emission signal of the probe upon providing F^- and TFA as a chemical inputs mimic the function of a memory device with ''write-read-erase-read'' functions and has also been utilized to construct a molecular key-pad lock security device system. Also, the probe showed sensitivity to detect the F^- in toothpaste. The mechanism of interaction has been confirmed by different spectroscopic data analysis.