Synthesis and Investigation of a Photoswitchable Copolymer Deposited via Initiated Chemical Vapor Deposition for Application in Organic Smart Surfaces

Abstract

The deposition of well-defined photochromic thin films is highly attractive but challenging when it comes to practical applications. In conventional wet chemistry methods, the choice of potential monomers and substrates is restricted to compatibility with the solvent. In addition to this, reversible photoisomerization of a photochromic compound covalently bound in a solid film can be hindered by chain interactions within the polymer matrix. After establishing a method to co-sublime solid chromophores in our previous work, we now present the successful copolymerization and detailed investigation of initiated chemical vapor deposition (iCVD)-prepared films of hydroxyethyl methacrylate (HEMA) cross-linked with a photoswitchable diazocine. The all-dry character of iCVD enabled the combination of a hydrophobic photochromic unit with a highly hydrophilic co-monomer without phase separation or defect formation, independent of the solubility of the used precursors. The so produced thin films stand out for their fast response upon irradiation with blue light, which minimizes the risk of photodegradation, as well as by full recovery of their stable resting state with a green light or mild heating. Finally, we demonstrate the deposition of our films on different materials such as glass or flexible polymeric substrates and present a straightforward approach for patterned coatings with a shadow mask. Using a conventional blue laser to induce photoswitching, it was possible to create accurate patterns in real time proving the applicability of our films in fields such as smart surfaces, labeling, or data storage.