Synthesis of a New Water‐Soluble Polymeric Probe and its Fluorescent Properties for Ratiometric Measurement of Near‐Neutral pH

Abstract

A new water‐soluble polymeric fluorescent probe, poly[allylamine‐co‐N‐4‐chloro‐6‐(4‐methylcoumarin‐7‐oxy)‐1,3,5‐triazinylallylamine] (PA‐TMC), has been designed and characterized for near neutral pH measurement in dual‐excitation ratio application. The probe was synthesized by using cyanuric chloride as a linker, 7‐hydroxy‐4‐methylcoumarin as a fluorophore, and polyallylamine as a water‐soluble molecular scaffold. It showed a large pH‐dependent shift of excitation peak from 320 to 360 nm with no change of emission wavelength of 448 nm. The pK_a value of the probe was 7.56, and the ratio R (I₃₆₀/I₃₂₀) of fluorescence intensities at the two excitation wavelengths of 360 nm and 320 nm was directly proportional to pH values over the range 6.8–8.5, which may be suitable for the pH monitoring of near‐neutral systems. Spectroscopic properties of the probe were also compared with the corresponding low molecular weight 7‐(4,6‐dichloro‐1,3,5‐triazinoxy)‐4‐methyl‐coumarin (TMC). The results showed that the incorporation of TMC into a water‐soluble polymer bearing a large number of hard base ligands offers both considerably improved selectivity for H⁺ and solubility in water, suggesting that such measure may be useful for preparing other probes with special functions.

Keywords:

• Water‐soluble polymeric fluorescent probe
• pH
• Ratiometric measurement
• Fluorescence

Acknowledgments

This work is financially supported by the NNSF of China and the Chinese Academy of Sciences.