Multichannel Chromogenic and Chiral Anions Recognition by Imidazolium Functionalized BINOL Derivatives

New imidazolium/benzimidazolium-containing receptors (R)-1–(R)-6 were developed as multifunctional receptors for both chromogenic and chiral anion recognition through multichannel. The ?uorescence spectra of (R)-1 showed a distinct and intense peak at 454, 474 nm with AcO⁻ and F⁻, respectively, indicating that (R)-1 can be applied to the detection of fluoride and acetate ions by naked eye. Receptor (R)-5, containing a lipophilic dodecyl appendage at imidazolium nitrogen, exhibited larger fluorescent responses than (R)-1. The ratio of fluorescence enhancement for (R)-5 with AcO⁻ (I₄₆₀/I₃₆₉=16) and F⁻ (I₄₈₅/I₃₆₉=11) was 32-fold and 18-fold over (R)-1 with AcO⁻ (I₄₅₄/I₃₆₉=0.5) and F⁻ (I₄₇₄/I₃₆₉=0.6), respectively. Less electron-deficient benzimidazolium receptor (R)-2 only gave fluorescence enhance at 555 nm for F⁻. Only chelation enhanced quenching (CHEQ) effect was obtained in the case of mono-imidazolium receptor (R)-4. Furthermore, (R)-1 and (R)-5 displayed a remarkable binding ability for the t-Boc alanine anion with interesting enantioselectivity [K_L/K_D=4.5 for (R)-1 and 4.1 for (R)-5)], whereas only negligible enantioselectivity ability (K_L/K_D=1.1) was obtained by using C₁ symmetric receptor (R)-4.