Abstract
Spatially programmable surface properties are important building blocks for future microfluidic and biosensor devices. We demonstrate switching of a photochromic surface with a blue organic light-emitting diode (OLED) suitable as an integrated on-chip light source. The surface of a positive polydimethylsiloxane replica of a fresh lotus leaf is covalently functionalized with a photoswitchable azobenzene self-assembled monolayer employing “click chemistry.” 80% of the azobenzene molecules are switched from cis to trans state within 4 min of OLED irradiation. A spatially resolved study of the azobenzene switching properties on the naturally inhomogeneous lotus surface is conducted evaluating the transmission of a 355-nm laser beam. In the area of the leaf veins the highest change in the relative transmission of 100% is obtained upon switching from trans form to cis form under UV illumination. In comparison, an azobenzene-functionalized flat glass surface exhibits only a 0.5% change in the relative transmission.
Highlights
IN recent years, more and more functionalities have been shown with photochromic molecules, controlling, e. g., adsorption and desorption of proteins or ligands [1] or adhesion of cells [2], [3]
The lotus structure highly increased the normalized relative transmission difference between the trans and cis state compared to a flat quartz substrate
We created surface maps showing the largest switching effects on the leaf veins. To utilize this for a larger surface, either a new stamp could be assembled from leaf vein sections or the micro-/nanostructure of the veins could be reconstructed artificially
Summary
IN recent years, more and more functionalities have been shown with photochromic molecules, controlling, e. g., adsorption and desorption of proteins or ligands [1] or adhesion of cells [2], [3]. The use of a single UV LED is proposed to switch the entire surface to the cis state We utilize the functionalization of an artificial PDMS lotus leaf based on a variation of the process by Sun et al with azobenzene molecules. A spatially resolved study of the switching properties of the naturally inhomogeneous azobenzenefunctionalized artificial lotus leaf is presented. For this purpose, we scan the transmission of the sample with a laser at a wavelength of 355 nm, where the absorption difference of azobenzene cis and the trans isomers is high.
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