Synthesis, Characterization, and Photochromism Study of Two Spiropyran Molecules with a Terminal Alkynyl Functional Group and Their New 1,2,3-Triazoline-containing Derivatives

The spiropyran derivatives are known for their good photochromic properties. These photochromic compounds are isomerized between two forms; merocyanine is the open-ring form and spiropyran is the closed-ring form. In this work, two spiropyran derivatives (compounds 1 and 2) with the N-alkynyl functional group are prepared. The click reactions of these spiropyran derivatives with 1-azido-4-nitrobenzene and (azidomethyl)benzene are studied. For this purpose, 3,3-dimethyl-2-methylene-1-prop-2-ynyl-2,3-dihydro-1H-indole is synthesized, which is then reacted with 3- and 5-nitrosalicylaldehyde. The FT-IR, 1H-NMR, and 13C-NMR spectra of the reaction products are used for their characterization. The solutions of the products in methanol are prepared, and their UV–visible spectra are investigated. The darkening of the crystals of compound 1 upon exposure to the UV irradiation indicates that the spiro C–O bond in this compound is weaker than that in compound 2, which is due to the presence of the nitro group in the para position relative to this bond, and consequently, the stabilization of the open-ring form.