Reversible Light-Induced Morphological Change in Langmuir−Blodgett Films

Abstract

An amphiphilic anionic azobenzene derivative, soluble in water, formed a monolayer on an aqueous subphase containing a water-soluble polycation. The monolayers were transferred onto solid substrate by the Langmuir−Blodgett (LB) technique. XPS measurements showed that ion exchange reaction proceeded almost completely at the air−water interface and that the ratio of the monomer unit of the polycation to the azobenzene was almost unity. UV/vis absorption and IR measurements indicated that the azobenzene photoisomerized reversibly in the LB films on alternate illumination with UV and vis light. Furthermore, a reversible morphological change induced by light was observed in the LB films with AFM. Before illumination, the surface of the single-layer LB film was very smooth with a surface undulation of less than 1 nm. On illumination with UV light, however, a number of hills, with the height of ca. 5 nm and the diameter of the base of ca. 100 nm, appeared on the film surface. These structures almost disappeared on illumination with vis light. This indicates that the widely accepted assumption that photoisomerization should not change the two-dimensional structures significantly does not hold in the present case.

Gold-Colored Organic Crystals Formed from an Azobenzene Derivative

“…They reported that crystals of p-conjugated compounds with a thiophene-pyrrole-thiophene chemical skeleton produce a gold color 5) . The aggregation of azobenzene derivatives has been extensively studied, and they have been found to form layers of J-aggregates or H-aggregates on solid substrates 6,7) . However, most of these studies were limited to the photoisomerization of several layers consisting of J-or H-aggregates; there are no reports on the color of crystals formed by stacking of a number of monolayers formed from the Jaggregates of an azobenzene derivative.…”

Dynamic Photoresponsive Functions in Organized Layer Systems Comprised of Azobenzene-containing Polymers

“…Matsumoto et al 43,44 have prepared LB films consisting of an ion complex formed between an anionic Az derivative and a cationic polymer. A very flat surface in the ion-complex LB monolayer on mica is observed before illumination.…”

Structures of Langmuir-Gibbs Films Consisting of Long-Chain Fatty Acid and Water-Soluble Surfactants

“…Arachidic acid is a typical Langmuir-film-forming molecule and forms stable Langmuir films. Because of the attractive electrostatic interactions, Langmuir films of arachidic acid induce the adsorption of cationic molecules 21 and polymers 22 , as well as the crystallization of proteins 23 and inorganic compounds 24 . We avoided these attractive electrostatic interactions because the strong attractive interactions, if present, may dominate the interactions between arachidic acid and the water-soluble surfactants.…”