A novel oxazole-based fluorescence sensor towards Ga3+ and PPi for sequential determination and application

•A novel fluorescence sensor (G2) was designed through.•5-(naphthalen-1-yl)oxazole-4-carbohydrazide and 4-(diethylamino)-2-hydroxybenzaldehyde.•G2 could be acted as an “off–on-off” sensor to sensitively and selectively determinate Ga3+ and PPi based on PET and LMCT mechanism.•The LOD values for Ga3+ and PPi were 3.11 nM and 62.6 nM, respectively.•The optimized structure, orbital energy and electrostatic potential were gained by theoretical calculation to demonstrate the sensing mechanism.•G2 was successfully applied for monitoring Ga3+ and PPi in tap water samples and constructing molecular logic gate.