In this work, we demonstrate the first synthesis of photochromic polymer thin films via initiated chemical vapor deposition (iCVD) using bifunctional, crystalline styrenediazocine as a photochromic unit. Since it represents a solid compound, an innovative custom-made sublimation unit is introduced, which allows the sublimation of the chromophore as well as its transport inside the reactor chamber, maintaining the functionality of the photoswitch. Styrenediazocine was co-polymerized with 1,3,5trivinyl-1,3,5-trimethylcyclotrisiloxane (V 3 D 3 ), a heterocycle with triple vinyl functionality, in a radical polymerization reaction from the gas phase. The structural as well as functional properties of the resulting films were characterized by various methods, including X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared (FT-IR) spectroscopy, and UV−vis spectroscopy. It could be confirmed that, via iCVD, photoswitchable polymer thin films have been obtained. The polymer is based on a copolymer structure where all photoswitchable molecules are covalently bonded in the main polymer chain. Our approach could pave the way for a completely new class of high-quality, photochromic thin films that are basically applicable on almost every kind of substrate for novel, interdisciplinary application fields, where particularly classical wet chemistry methods cannot be applied.

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.