Synthesis, fluorescence properties of diaminodicyanoquinodimethanes and their application of sensing pH in extremely acidic environment

Abstract

In this work, a series of diaminodicyanoquinodimethanes (DADQ) were designed and synthesized by using tetracyanoquinodimethane (TCNQ) and secondary amines as reactants. They are found to be novel D-π-A-type molecules with dual-state emission (DSE) and can be applied to pH detection. For probe T4, when the pH value is greater than 2.6, T4 is a yellow solution in THF and shows green fluorescence under ultraviolet light. As the pH value decreases, the fluorescence intensity gradually weakens and the yellow solution slowly becomes lighter. When the pH value is lower than 0.8, the fluorescence intensity approaches the quenched state, and the yellow solution is nearly colorless. No significant interference with pH detection has been observed in the presence of various metals and anions. In addition, T4 can be used for real-time and reversible pH sensing. Finally, the T4 probe has not only been used for the detection of pH value in solutions, but also has been successfully made into portable test strips for visual detection.