A spectroscopic study on medium polarity in fluorous alcohol

The paper describes the polarities of three fluorous (F) aliphatic alcohols: perfluorinated tert-butanol (F-t-BuOH), n-butanol (F-n-BuOH), and n-heptanol (F-n-HepOH). For the purpose, we conducted absorption and fluorescence spectroscopies of coumarin 153 (C153) and 102 (C102) in three F and 13 non-fluorous (non-F) alcohols and determined their maximum energies: νa (absorption) and νf (fluorescence). We obtained linear relationships between the Stokes shifts of the dyes (i.e., (νa − νf)) and a medium polarity parameter for 13 non-F alcohols, f(x): f(x) = [(Ds − 1)/(2Ds + 1) − (n2 − 1)/(2n2 + 1)], where Ds and n were the dielectric constant and refractive index of a solvent, respectively. By comparing the Stokes shifts of the dyes in three F alcohols with those in 13 non-F alcohols (i.e., (νa − νf) vs. f(x) plot), the Ds values in F-t-BuOH, F-n-BuOH, and F-n-HepOH were evaluated to be 2.7–3.9, 4.3–5.1, and 4.0–5.2, respectively, while those in the relevant non-F alcohols were 12.5, 17.5, and 12.9, respectively. Thus, the present experiments demonstrated that the polarities of these F alcohols were much lower than those of the relevant non-F alcohols.