A dual-mode colorimetric/fluorescent probe based on perylene: Response to acidic pH values

The pH value plays critical roles in many chemical and physiological processes and exploring a more effective and sensitive method for the detection of pH is great need. A new “off-on” pH chemosensor, N,N-bis[(2-furan)-ethyl]-3,4,9,10-perylene tetracarboxylic diimide (FEPTD), was designed and synthesized by Schiff-base condensation reaction with 2-furaldehyde and perylene-3,4,9,10-tetracarboxylic acid dianhydriden as the starting materials. FEPTD as a fluorescent probe was used for highly detecting pH values on the basis of molecular fluorescence spectrophotometry with the excitation wavelength of 300 nm in EtOH/Buffer solutions. Meanwhile, FEPTD was also applied for the detection of H+ in test paper and cotton. FEPTD exhibited excellent solubility and stability in EtOH/Buffer (V:V, 1:1) with obvious “off-on” fluorescence response towards pH changes due to photo-induced electron transfer (PET) processes. The linear response ranges of FEPTD for pH detection in acidic system are from 4.32 to 3.10 with pKa = 3.69. Moreover, FEPTD showed an evident naked-eye color changes, where pale pink solution of FEPTD turned deepened with the fluorescent color varying from colorless to brilliant yellow. 1H NMR titration and density function theory calculations proved the possible sensing mechanism. Finally, FEPTD was successfully applied for the detection of H+ in test paper and cotton.