The contrastive study of two thiophene-derived symmetrical Schiff bases as fluorescence sensors for Ga3+detection

Two thiophene-derived symmetrical Schiff bases R (N'2,N'5-bis((E)-2-hydroxybenzylidene)thiophene-2,5dicarbohydrazide) and E (N'5,N'7-bis((E)-2-hydroxybenzylidene)-2,3-dihydrothieno[3,4-b][1,4]dioxine5,7-dicarbohydrazide) were synthesized as sensors for Ga3+ detection via fluorescence turn-on strategy. After chelation with Ga3+, both of them displayed the significant fluorescence enhancement in MeCN/H2O buffer solution. Meanwhile, R and E showed ultralow detection limits of 3.90 x 10-9 M and 3.97 x 10-9 M, respectively. Differently, the sensor E featured much higher selectivity and anti-interference for Ga3+ detection than R in the presence of other cations such as In3+, Zn2+ and Cu2+. The Job's plots revealed a 1:2 stoichiometry between sensors and Ga3+ with the association constant of 3.89 x 109 M2 for R and 8.59 x 109 M2 for E, respectively. To further explain the differences of sensing performance between the two sensors, the theoretical researches were executed through the molecular configuration, charge distribution, molecular orbitals, electronic transitions and energy variation. Besides, E could exhibit an efficient recognition of Ga3+ in the water samples.