Self-Assembled Thin Solid Films of Dioctadecyldimethylammonium Cinnamate Lamella Units That Control the Photostationary State of E−Z Photoisomerizations

Abstract

UV illumination of dioctadecyldimethylammonium cinnamates (C18 trans-cin and C18 cis-cin) was found to result in the E-Z photoisomerization of the cinnamate moieties in self-assembling multilamella films. In the present case, a common photostationary state (pss), which can usually be observed in solution, was not seen in the photolysis of the self-assembled material films of C18 trans-cin and C18 cis-cin having a bimolecular (bilayer)-unit lamellar structure. Both the E-and Z-isomers are difficult to isomerize and exhibit different E/Z ratios, 73:27 and 10:90, respectively, even under prolonged UV irradiation. However, the same E/Z ratio (15:85) could be attained at the pss from either isomer in a monolayer-unit structure. The E/Z ratios were found to change abruptly upon heat treatment at around 55 °C before photoisomerization, implying a thermal structural change in the films. Analysis of X-ray diffraction, differential scanning calorimetry, and polarized IR and UV-vis spectroscopic investigations have indicated that the solid films have a characteristic multilamellar structure consisting of bilayer units when they are cast on the silica glass without heat treatment above 55 °C. Moreover, the solid films preheated to 80 °C were composed of an interdigitated monolayer unit having a loose packing structure. This result is in contrast to the bilayer-unit structure of the solid films where E-Z photoisomerization of both isomers is suppressed.

Sum-Frequency Generation Spectroscopy of Cinnamate Modified Cellulosic Polymer at the Air–Water Interface

“…The preparation method of the polymer films can also play a significant role in the photochemical behavior upon UV exposure. As an example, Ohtani et al have shown that the photoreactivity of cinnamate groups in dioctadecyldimethylammonium/cinnamate ions self-assembled films varies according to the heat treatment of the films before photoirradiation which leads to different molecular organizations. Also, in a previous work, we have reported that cinnamate groups of modified cellulosic polymers mainly undergo either dimerization in spin-coated films or isomerization in networks synthesized with an exogeneous cross-linker …”

Reversible Light-Driven Structural Changes between the Mono- and Bilayer Stacking Alignments in 4-Octadecyloxystilbazolium Arylcarboxylate Films

“…We have previously reported that structural changes in 1:1 ion-pair composite bilayer films consisting of dioctadecyldimethylammonium bromide and cinnamic acid take place not only in dispersion but also when cast on glass slides, and that such changes can be induced by a photochemical E − Z photoisomerization and/or a [2+2] photocycloaddition of the cinnamate regions. − These self-assembling structures have been revealed to be variable with the photochemical transformations of the component olefins.…”