Thermodynamic equilibrium of the transitions between the closed and open forms of a spiropyran-based molecular switch monitored via variable-temperature 1H NMR spectroscopy

Abstract

A benzothiazole spiropyran exhibited both photochromic and acid-chromic properties. Via variable-temperature ¹H NMR spectroscopy, the equilibrium constants K^ϕ, ΔH^ϕ and ΔS^ϕ of the ring-closed to ring-opened transition were calculated as ca. 10⁻⁷, 38.62 kJ mol⁻¹ and −5.55 J K⁻¹ mol⁻¹, respectively. This is of importance for the application of new spiropyrans.