Experimental insights reveal how polymer composition affects photoacidity and hydrolytic stability in water, suggesting potential applications in energy conversion.
Spiropyran-based polymers are widely studied on account of their multifaceted stimuli-responsive behaviours. However, their photoacidic characteristics in aqueous environments remain overlooked. Here, we synthesized a series of statistical copolymers containing sulfopropyl methacrylate units (SPMA) alternated with spiropyran methacrylate units in their photoacidic, protonated merocyanine form (MCHMA). We studied the behaviour of these (SPMA-co-MCHMA) polyelectrolytes in water and found that polymer constitution significantly enhances the hydrolytic stability of the MCH moieties, whereas polymer composition can be used as a tool to program the quantum yield of isomerization and the photoacidity – i.e., the acidity difference between their ground state (trans-MCH) and metastable state (cis-MCH) in pKa units. Exposure to mild 500 nm light enables these polyelectrolytes to reversibly dissociate protons, causing metastable fluctuations as large as 3 pH units in the surrounding aqueous medium. The results presented here hold promise in the development of robust light-to-ionic energy conversion devices.
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Gericke et al. (2025) studied this question.
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