Abstract
Photoisomerization in solids lays the foundation for photoswitching in applications such as energy harvesting, photoactuators, coatings, etc. However, low penetration of light into materials can limit the efficiency of photoisomerization in bulk materials. Consequently, the improved light penetration depth is a key requirement that must be considered when utilizing molecular photoswitches in bulk materials applications. Two azobenzene derivatives with substitution in the N=N bond’s ortho position, including electron-donating methoxy groups and electron-withdrawing fluorine atoms, are chosen as the research subjects. A remarkable red-shifted n–π* absorption appears on both azobenzene derivatives, enabling efficient E to Z switching to be photoinduced with visible light. E to Z photoisomerization of two azobenzene derivatives in thin films is investigated as a function of film thickness. Also, the method of preparing a series of azobenzene derivatives thin films with different thicknesses is described. The E to Z isomerization is induced by subjecting the films with different thicknesses to the LED light to the photostationary state (PSS) in film, and the E/Z ratio is determined by 1H NMR spectroscopy. Ultraviolet (UV) light penetration depth is also determined, showing that UV light penetrates only marginally into these azobenzene films.