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: ν a (absorption) and ν f (fluorescence). We obtained linear relationships between the Stokes shifts of the dyes (i.e., ( ν a − ν f )) and a medium polarity parameter for 13 non- F alcohols, f ( x ): f ( x ) = [( D s − 1)/(2 D s + 1) − ( n 2 − 1)/(2 n 2 + 1)], where D s 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., ( ν a − ν f ) vs. f ( x ) plot), the D s 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.