Thermal stability and photochromic properties of a fluorinated indolylfulgimide in a protic and aprotic solvent

The photochromic properties and thermal stability of a newly synthesized fluorinated N-ethoxycarbonylmethyl indolylfulgimide substituted on the imide nitrogen were examined in a protic and aprotic environment. The absorption spectra and extinction coefficients of the Z- and C-forms of the fluorinated indolylfulgimide (open and closed, respectively) were measured in a binary 70/30 ethanol/water system and in toluene. The results demonstrated a favorable bathochromic shift of the absorption maxima for both the open and closed forms of the fulgimide when the solvent was changed from aprotic toluene to protic aqueous ethanol. In addition, the photochemical stability of the new fulgimide was found to be high (0.056 and 0.020% degradation each time the fulgimide is cycled between the open and closed form in 70/30 ethanol/water and in toluene, respectively). The thermal stability of both forms of the fulgimide in 70/30 ethanol/water at 50 °C, toluene at 80 °C, and polymer film (PMMA) at 80 °C was measured using UV–vis and/or 1H NMR spectroscopy. Both forms of indolylfulgimide display high hydrolytic stability in 70/30 ethanol/water at 50 °C, with the Z- and C-forms degrading 1.3 and 1.2%/day respectively, based on 1H NMR data. At 80 °C in toluene the less stable Z-form lost about 20%/day.