Diamidonaphthalenodipyrrole-derived fluorescent sensors for anions

• Naphthalenedipyrrole is useful in construction of fluorescent anion sensors.
• It can be fine-tuned through small structural modification at the sensor periphery.
• It provides efficient identification of the dihydrogen phosphate or benzoate anions.

We describe the synthesis and properties of bisamide derivatives of naphthalenedipyrrole, which represent a convenient platform for the construction of fluorescent anion sensors. As we show, the spectroscopic properties of such sensors can be fine-tuned through small modifications of the structure at the sensor periphery. The strong fluorescence of these compounds is perturbed through the binding of anionic species in the binding pocket through four hydrogen bonds. Importantly, these effects depend on the nature of the anionic guest, its concentration, and the specific structure of the receptor host. For instance, in the case of one derivative (2a) the fluorescence is selectively quenched upon addition of PhCO2−, while other anions do not have an effect on its spectral properties. In another case (2b), only H2PO4− triggers a spectacular enhancement of fluorescence (more than five times higher intensity), while other anions do not change its spectral properties. Such selective responses are related to the selectivity of the anionic species binding, which can be controlled with the structure of the binding pocket. Overall, the study demonstrates that a diamidonaphthalenedipyrrole platform can be used to construct selective sensors for anions that allow for fast and efficient identification of the desired anion present in the analytical samples.