The spiropyran derivatives can exist in two forms, the closed-ring spiropyran form and the open-ring merocyanine (MC) form. The SP form could be converted into the MC form upon UV irradiation. In this work, some 1′,3′,3′-trimethylspiro[chromene-2,2′-indoline] derivatives containing the nitro and formyl groups are synthesized via the reaction of 1,3,3-trimethyl-2-methylene-5-nitroindoline with the corresponding salicylaldehyde derivatives. These compounds have different photochromic behaviors. The synthesized photochromic molecules are characterized by the FT-IR, ¹H-NMR, and ¹³C-NMR spectroscopic techniques. In order to investigate the photochromic properties of these compounds, the UV–visible spectroscopic analyses of their methanolic solutions before and after exposure to a UV lamp (in the spectral range of 360–400 nm) are studied.

Graphic abstract