Two 5-(thiophene-2-yl)oxazole derived “turn on” fluorescence chemosensors for detection of Ga3+ and practical applications

Two (5-(thiophene-2-yl)oxazole derived chemosensors, N′-(2-hydroxybenzylidene)-5-(thiophene-2-yl)oxazol-4-carbonylhydrazine (L1) and N′-(3-ethoxy-2-hydroxybenzylidene)-5-(thiophene-2-yl)oxazol-4-carbonylhydrazine (L2), were designed and synthesized via a fluorescence turn-on strategy to specifically recognize Ga3+. Both L1 and L2 showed highly sensitive and selective fluorescence responses toward Ga3+ in the DMSO/H2O buffer solution and exhibited more effective anti-interference performance over other coexisting metal ions including Al3+ and In3+. The limits of detection for Ga3+ were found to be 6.23 × 10−8 M and 1.15 × 10−8 M with L1 and L2, respectively. Job's plots and mass spectrometry (ESI-MS) suggested a 1 : 2 complexation ratio of sensors to Ga3+ with binding constants of 8.54 × 108 M2 for L1 and 1.06 × 108 M2 for L2. The proposed interaction mechanism was further supported by density functional theory. In addition, both sensors were applied to the detection of Ga3+ in environmental water samples.