Effect of fluorinated ammonium counterions upon the reversibility in E–Z photoisomerization of azobenzene ion pair films

Alternate light illumination of ion-pairs of (3-perfluorooctanecarboxamido)propyltrimethylammonium azobenzene-4-carboxylate (FOAM–AzoB) at 340 and >440 nm was found to initiate a reversible photoisomerization between the E- and Z-azobenzene chromophores in multi-lamella films. This was in sharp contrast to the case of films involving the corresponding unfluorinated ion-pair, 3-(octanecarboxamidopropyl)trimethylammonium azobenzene-4-carboxylate (HOAM–AzoB) in which no substantial isomerization could take place. These photochemical characteristics are discussed here in terms of the free space surrounding the azobenenzene units of the ion-pairs molecularly packed within the films. Characterization studies using XRD and polarized spectroscopy revealed that the FOAM–AzoB stacked films consist of loosely packed interdigitated monolayers whereas HOAM–AzoB was found to form compactly packed bilayer stacked films.