Synthesis and properties of photochromic biindenylidenedione derivatives containing thiophene groups, and new insights into the reaction of 2,2′-biindanylidene-1,1′,3,3′-tetraone with Grignard reagent

Three indenone derivatives (1: 2-[3′-hydroxy-3′-(2-thienyl)indanone-2′-yl]-3-(2-thienyl)indenone; 2: trans-anti-3,3′-(2-thienyl)-3,3′-dihydroxy-[2,2′-bi-1H-indene]-1,1′-dione and 3: trans-syn-3,3′-(2-thienyl)-3,3′-dihydroxy-[2,2′-bi-1H-indene]-1,1′-dione) were obtained in a one-pot reaction of 2,2′-biindanylidene-1,1′,3,3′-tetraone with 2-thienylmagnesium bromide. Their structures were characterized by means of IR, 1H NMR, MS, elemental analysis, and X-ray crystallography. The photochromic and photo-induced radical behaviors of these compounds were investigated by means of solid UV–vis spectroscopy and electron spin resonance (ESR) spectroscopy. The results show that compounds 2 and 3 exhibit photochromism in the solid state, whereas compound 1 does not. The relationship between the crystal structures and photochemical properties is also discussed. Based on the formation and product distribution of compounds 1, 2, and 3, a plausible pathway is suggested for the reaction of 2,2′-biindanylidene-1,1′,3,3′-tetraone with 2-thienylmagnesium bromide. The findings obtained in this study also provide new insights into the addition–oxidation mechanism for the reaction of 2,2′-biindanylidene-1,1’,3,3’-tetraone with Grignard reagent.