Recognition of carboxylic acids and phosphonic acids using 1,8-diphenylnaphthalene-based diguanidine

Abstract

Abstract A diphenylnaphthalene-based diguanidine (1) has been designed and synthesized for the recognition of dicarboxylic acids and diphosphonic acids. The diguanidine 1 forms 1:1 complexes with the dicarboxylic acids and the diphosphonic acid derivatives in a DMSO solution, and the formation of the complexes was determined by DOSY NMR spectroscopy. The weak yellowish fluorescence of the diguanidine 1 in a DMSO solution turned to a strong bluish fluorescence after the addition of 1,3-benzenediacetic acids 3. However, after the addition of other types of aliphatic dicarboxylic acids, such as α,ω-dicarboxylic acids, only a weak yellowish fluorescence was observed and selective recognition of the 1,3-benzenediacetic acids 3 was developed. On the other hand, for the recognition of diphosphonic acid derivatives (5–7), a light blue, blue or pinkish fluorescence was observed. Interestingly, the binding mode on the guanidyl group (two existing types of binding modes toward three nitrogen atoms) with oxoacids were successfully determined by the 2D NOESY analysis. The fluorescence quantum yields (Φfl) were moderately increased by the introduction of the guanidyl group and binding with dicarboxylic acids 3 than that of the 1,8-diphenylnaphthalene itself. These fluorescence characteristics of the diguanidine 1 are applicable for the detection of dicarboxylic acids and diphosphonic acids.