Photoisomerization of Azobenzene Grafted to Layered Silicates: Simulation and Experimental Challenges

Abstract

Molecular dynamics (MD) simulation has been employed to examine the molecular-level orientation and reorganization of model azobenzene derivatives in the interlayer space of layered silicates upon laser excitation in comparison with existing X-ray diffraction data and UV/vis absorption measurements. MD results show uniform reversible changes in basal plane spacing of montmorillonite up to 2.8 A (14%) upon trans−cis isomerization of attached photoactive surfactants such as (4,4′-phenylazophenyl)diammonium ions and (4-phenylazophenyl)ammonium ions. Uniform, significant reponses are supported by the presence of cointercalate to compensate changes in interlayer density, by conformational rigidity and upright orientation of the azobenzene-containing surfactants on the mineral surface, and a medium-to-high packing density. Experimentally, Okada et al. have shown nonuniform reversible optical switching of the gallery height for semiflexible surfactants up to 10 A (41%) in the presence of phenol and uniform rever...