RESONANT AND NONRESONANT INVESTIGATIONS OF AMPHIPHILIC AZOBENZENE DERIVATIVES IN SOLUTION AND IN MONOLAYERS AT THE AIR-WATER-INTERFACE

The characteristics of molecular organization, aggregation, and cis-tr ans isomerization of azobenzene moieties, confined in the hydrophobic region of monolayers of an amphiphilic azobenzene derivative (A820Py) at the air/water interface, have been investigated. As a result of con formational changes accompanied by the isomerization process, the mole cular packing within the monolayer at constant surface area and thereb y the molecular organization show pronounced changes. The surface-enha nced UV-vis reflection spectra of A820qr monolayers show the presence of both monomers and H aggregates. Cis-trans isomerization leads to ch anges in the resonant reflection spectrum, the surface potential, and the Brewster angle reflectivity of the monolayer. The isomer compositi on of the photostationary states of pure A820Py monolayers has been de termined through the analysis of UV-vis reflection spectroscopic data. The ratio of quantum yields of photostationary states of A820Py in so lution and in monolayers have been compared. The kinetics of the cis-t rans isomerization process in the monolayers have been followed by mea suring the resonant reflection, the surface potential, and the Brewste r angle reflectivity. The composition of the photostationary states ha s been analyzed in terms of the Fischer method. The monolayers prepare d at the air/water interface have been transferred to solid substrates such as glass or quartz plates. A persistent pattern was written in t he single monolayer by exposing it to actinic radiation through a mask . Brewster angle microscopy was used to visualize the created microsco pic pattern of trans and cis isomers.