A fluorescent pH chemosensor based on functionalized naphthalimide in aqueous solution.

The synthesis of functionalized naphthalimide (compound 1) and its application for the preparation of pH chemosensor was described. The fluorescence enhancement of compound 1 with the increase of hydrogen ion concentration is based on the hindering of photo-induced electron transfer (PET) from aliphatic amine group to the naphthalimide. The comparison of this method with some other fluorescence methods based on naphthalimide for the measurement of pH indicated that the method can be applied in aqueous solutions rather than organic solutions. The analytical performance characteristics of the proposed pH chemosensor were also investigated. The chemosensor can be applied to the determination of pH between 3.20 and 7.80. Common inorganic ions do not show obvious interference for pH measurements. Moreover, the response of the chemosensor for pH is fast (response time less than 3 min). In addition, the chemosensor has been used for determination of pH in urine samples with satisfactory results.