Three Novel Rhodamine 6G-Based Colorimetric and Fluorescent pH Switches.

Abstract

Three rhodamine 6G derivatives (REHA, RETA and REDA) were designed and synthesized by connecting rhodamine 6G and 3-methyl-2-thiophenal with hydrazine hydrate, ethylenediamine and diethylenetriamine, respectively. In CH3CN/H2O (50/50, v/v), the absorbance of REHA, RETA and REDA at 528nm was suddenly enhanced by 3.2, 3.8 and 7.2 times within the pH range of 3.03-2.31, 3.05-2.32 and 3.06-2.34, respectively, and the solution changed from colorless to pink. Meanwhile, the maximal fluorescence intensity sharply increased by 53.9, 26.6 and 24.9 times in the pH range of 3.86-3.46, 3.88-3.47 and 3.89-3.48, respectively, and the solution changed from dark to bright yellow-green fluorescence. REHA, RETA and REDA can act as highly selective and sensitive colorimetric and fluorescent pH switches with good recyclability and anti-interference ability. The response mechanism of REHA, RETA and REDA to pH was studied by 1H NMR spectroscopy, and their application in indicating small pH changes in dyeing wastewater was investigated.