Preparation of 4,4-Diaryl-2-(tricyanoethenyl)dithienosiloles and Vapor-Chromic Behavior of the Film

[reaction: see text] Reactions of 4,4-diphenyl- and 4,4-di(p-tolyl)dithienosilole with tetracyanoethene (TCNE) in DMF gave coupling products 4,4-diphenyl- and 4,4-di(p-tolyl)-2-(tricycanoethenyl)dithienosilole (1a and 1b) in good yield. The films of 1b exhibited vapor-chromism, and the color of the film changed from red to blue-purple upon exposure to the vapor of organic solvents such as ethanol, methanol, acetonitrile, ethyl acetate, acetone, and hexane. The color reverted to the original red upon contact with chloroform vapor, indicating that this process is reversible.