Simple hydrazide-based fluorescent sensors for highly sensitive and selective optical signaling of Cu2+ and Hg2+ in aqueous solution

•Two new water-soluble hydrazide-based fluorescent probes of PM1·HCl and PM2·HCl.•PM1·HCl selectively recognizes Cu2+ and Hg2+ in aqueous solution with different emission characteristics (blue-shifted for Cu2+ and red-shifted for Hg2+) and color changes.•Detection limits of sensor PM1·HCl for Cu2+ and Hg2+ were estimated to be 2×10−10M and 2×10−9M, respectively.•PM2·HCl also showed high sensitivity toward Cu2+ in aqueous media, and the detection limit was measured to be as low as 2×10−10M.