An ultrafast BODIPY single molecular sensor for multi-analytes (acid/base/Cu2+/Bi3+) with different sensing mechanism

Towards future practical applications, it is necessary to develop the fluorescent sensors with only single fluorophore and single receptor for multiple-analytes detection. In the present work, a novel molecular sensor containing single receptor (the naphthol-azomethine-phenol framework) and single fluorophore (BODIPY), NAP-BODIPY, has been designed and synthesize. Single crystal X-ray diffraction analysis reveals the keto-enamine rather than the enol-imine constitution of the ortho-hydroxy naphthalene azomethine moiety in NAP-BODIPY. As a consequence, along with the conversion between acid and basic conditions in the mixed DMSO/H2O, the enol-keto tautomerization occurs in the ortho-hydroxy naphthalene azomethine moiety of NAP-BODIPY, resulting in a diverse change over the electronic absorption and fluorescence emission spectra. Moreover, addition of Cu2+ into NAP-BODIPY solution leads to an obvious red-shift in the maximum absorption and the naked-eye observed change from pale-orange to magenta turbid due to the metal-induced aggregation interaction. Nevertheless, adding Bi3+ into NAP-BODIPY solution induces a remarkable enhancement over the weak fluorescence emission owing to the inhibition of photo-induced electron transfer process. Subsequent addition of Cu2+ into the NAP-BODIPY-Bi3+ (1:10) system triggers a triple-signal change associated with the metal displacement. This, in combination with the fast responsive time of NAP-BODIPY to acid/base/Cu2+/Bi-3+ (within several seconds), endows NAP-BODIPY an ultrafast-detecting sensor nature for multi-analytes. In particular, NAP-BODIPY can selectively stain lysosomes and therefore detect the pH change in live cells upon lysosomal acidification, revealing its great application potential for multiple-analytes.