Fabrication of Diazocine-Based Photochromic Organic Thin Films via Initiated Chemical Vapor Deposition
Maximilian H. Burk, Stefan Schröder, Widukind Moormann, Daniel Langbehn, Thomas Strunskus, Stefan Rehders, Rainer Herges, Franz Faupel
Abstract
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 1,3,5-trivinyl-1,3,5-trimethylcyclotrisiloxane (V3D3), 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.