Synthesis and Optical Properties of Aqueous Soluble Indolylfulgimides

Three novel aqueous soluble fulgimides, trifluoromethyl carboxylic acid indolylfulgimide 4, dicarboxylic acid indolylfulgimide 5, and carboxylic acid indolylfulgimide 6, were synthesized. Both 4 and 5 can switch back and forth between open and closed forms upon illumination with specific wavelengths of light, whereas 6 can only switch from the closed form to the open form. In sodium phosphate buffer (pH 7.4) at 37 °C, an unusual hydrolysis of the trifluoromethyl group of the closed form of 4 resulted in 5, which has an additional carboxylic acid group. The closed form of 5 was further decarboxylated to generate 6, which was not photochromic. In buffer, the open form of 4 degraded 20% after 10 days, while the closed form of 4 was converted to 5 rapidly. In buffer, both forms of 5 degraded less than 20% after 21 days at 37 °C, and 5 underwent 670 photochemical cycles before degrading by 20%. It is the most robust fulgimide yet reported in aqueous solution.