In order to investigate if RATU can be applied in nearly neutral pH scope, UV–vis absorption and fluorescence spectra of a series of RATU and RATU-Hg2+ CH3CN/H2O (1/99, v/v) solutions with different pH values were tested. As shown in Fig. 6, the absorbance and the fluorescence intensity of RATU-Hg2+ showed a small decrease with the increase of pH between 6.01 and 8.57, while those of the blank RATU almost kept stable at a very low level. The absorbance and the fluorescence intensity of RATU-Hg2+ were much higher than those of the corresponding blank RATU. Thus, RATU can colorimetrically and fluorimetrically detect Hg2+ in a pH span of 6.01–8.57 which was suitable for ecological and biological systems.