Ultra-fast pH detection in water by a responsive polymer containing a fluorescent dye David Londono de la Cruz , Roshan Singh-Morgan, Calum T. J. Ferguson and Rachel K. O’Reilly School of Chemistry, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK Stimuli-responsive polymers, have gained enormous attention due to their ability to generate a response when detecting weak changes in their surrounding environment such as pH, temperature, enzyme, light, electrical, redox and magnetic fields, ionic strength, etc. 1-4 These external stimuli usually induce an observable or detectable change in the polymer conformation. Among these, pH responsive polymers are known by their ability to accept or donate protons in response to pH changes and, therefore their structures. One way to induce these changes could be done by CO 2 that behaves as a weak acid in solution. Here, pH-responsive fluorescent polymeric particles are produced by emulsion polymerisation that contain a 4-nitrobenzo[c][1,2,5]thiadiazole as non- responsive dye moiety and N,N-di-ethylaminoethyl methacrylate (DEAEMA) as pH responsive unit. The addition of carbon dioxide to aqueous systems reduces the pH of the system and can be used as stimuli. It also induces conformational changes to the system that in turn enhances fluorescence, allowing easy detection. Upon the addition of carbon dioxide, a stark increase in fluorescence was observed after only 30s. Moreover, the addition of nitrogen results in a reduction of the fluorescence, demonstrating its reversible nature during several cycles, useful for potential gas sensing. Eventually the particles performance shows promising features for real time pH sensing, but further investigations must be conducted to maximize their potential. References 1. Hanbin Liu, Shaojian Lin, Yujun Feng and Patrick Theato, Chem., 2017, 8 , 12–23. 2. Anne B. Mabire, Quentin Brouard, Anaïs Pitto-Barry, Rebecca J. Williams, Helen Willcock, Nigel Kirby, Emma Chapman, and Rachel K. O’Reilly, Chem., 2016, 7 , 5943. 3. Dapeng Zhang, Yujiao Fan, Hui Chen, Sylvain TrØpout and Min-Hui Li, Chem. Int. Ed., 2019, 58 , 10260 –10265.Sebastian Perrier, Macromolecules, 2017, 50 , 7433-7447. 4. Matthieu P. J. Miclotte, Stefan B. Lawrenson, Spyridon Varlas, Bilal Rashid, Emma Chapman, and Rachel K. O’Reilly, ACS Polymers Au, 2021, 1 , (1), 47-58. 5. Wang, Y., Huo, M., Zeng, M. et al. CO2-responsive Polymeric Fluorescent Sensor with Ultrafast Response. J. Polym. Sci., 2018, 36 , 1321–1327. 6. Wei, Y. Gao, X. Li and M. J. Serpe, Polym. Chem. , 2017, 8 , 127-143.
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