Solvent Polarity Effects on the Mechanochemistry of Spiropyran Ring Opening

• DOI: 10.1021/jacs.3c11621
• Publication Date: 2024-02-03T15:13:35Z
• Authors: Yangju Lin; Tatiana B. Kouzne...; Alex G. Foret; Stephen L. Craig
• Keywords: Spiropyran; Merocyanine

The spiropyran mechanophore (SP) is employed as a reporter of molecular tension in wide range polymer matrices, but the influence surrounding environment on force-coupled kinetics its ring opening has not been quantified. Here, we report single-molecule force spectroscopy studies SP five solvents that span normalized Reichardt solvent polarity factors (ETN) 0.1–0.59. Individual multimechanophore polymers were activated under increasing at constant 300 nm s–1 displacement an atomic microscope. extension results plateau force–extension curve, whose midpoint occurs transition f* corresponds to required increase rate activation approximately 30 s–1. More polar lead mechanochemical reactions are easier trigger; decreases across series solvents, from high 415 ± 13 pN toluene low 234 9 n-butanol. trend reactivity consistent with developing zwitterionic character going ring-opened merocyanine product. dependence (Δx‡) was calculated for all cases and found ETN, which interpreted reflect shift state later more productlike position. inferred position double-well (two-step) reaction potential energy surface, second step determining, intermediate than