Fig. 4

a The PL spectra of aqueous solutions (1 mmol/L) of BMIP with different concentrations (0, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0 mol/L, respectively) of OHˉ. b The changes of fluorescence intensities of BMIP solutions (1 mmol/L) with different concentrations (3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0 mol/L, respectively) of OHˉ in water. c The PL spectra of aqueous solution (3 mol/L OHˉ) of BMIP (1 mmol/L) at different times (10 s, 46 s, 83 s, 116 s, 147 s, 179 s, 211 s, 240 s, 275 s, 307 s, 337 s, 369 s, respectively). d The PL spectra of aqueous solutions (1 mmol/L) of BMIP (3 mL) at different conditions (black line, BMIP solution without any additives; red line, BMIP solution after adding NaOH (3 mol/L); purple line, BMIP solution after adding NaOH (3 mol/L) and then the solution pH became neutral by adding sulfuric acid; blue line, BMIP solution after adding NaOH (3 mol/L), then the solution pH became neutral by adding sulfuric acid and finally adding NaOH (3 mol/L) again)