Light-emitting persistent radicals for efficient sensor devices of solvent polarity

Radical adduct 1 and the novel [4-(N-indolyl)-2,6-dichlorophenyl] bis(2,4,6-trichlorophenyl)methyl radical (2) exhibit intense fluorescence emission in cyclohexane in the red wavelength region. The intensity and the wavelength of the emission band are drastically dependent on the polarity of the solvent. Besides, radical adduct 2 has been fully characterized by differential scanning calorimeter, showing a high thermal stability and a clear glass nature to form excellent films.