Simple and efficient ratiometric fluorescent probes for near-neutral pH in aqueous solutions

Two ratiometric fluorescent pH probes of 2,6-diaminopyridine (DAPD) and 2-amino-5,7-dimethyl-1,8-naphthyridine (ADMND), though simple-structured, show good sensitivity to near-neutral pH range (6.0-8.0) in aqueous solutions. Further studies indicate that the 2-amino groups on pyridine or naphthyridine ring play an important role in the pH-dependent fluorescence spectral properties of these dyes.