The standard Gibbs energy of hydrophobic interaction of phenosafranine (PS+) dye with Nafion(R) film (Delta G(h)(o)) was estimated as - 21.17 +/- 0.04 kJ mol(-1). The positive and negative scans of PS + in Nafion(R) film showed markedly different electrochemical behavior. The apparent diffusion coefficient D-app(red) calculated for the reduced PS+ (PSH2+) was higher than that of the PS+ (D-app(ox)) in Nafion(R) film, explained by the greater interaction of PS+ with the hydrophobic region of the Nafion(R) film than the PSH2+. Addition of 2-propanol to the supporting electrolyte (0.5 M H2SO4) led to the release of PS+ from the electrochemically inactive to the electrochemically active regions of the Nafion(R) film. In the in situ spectrocyclic voltammetry study of PS+ in Nafion(R) film, the formation of leuco dye (PSH2+) was observed during the reduction of PS+. The formation of monomer PS+ and dimer (PS+)(2) was also observed in the in situ spectral study during the oxidation of PSH2+ in Nafion(R) film aside from its electrochromic behavior.