Photochemical Surface Degradation in Spiropyran Based Films

Abstract

Functional coatings based on molecular photoswitches hold promise in photoswitching of surface properties and especially solvent contact angles. Combining molecular photoswitches with other components creates shapeable amorphous rather than crystalline surfaces. Here, a potentially polymerisable thioctic acid unit was combined with a spiropyran photochromic switch (spiropyran thioctic ester (SPTE)) to form amorphous photoswitchable films. The photochromism of the films shows reversibility. However, we show that the increase in surface polarity observed upon switching with UV light is due in large part to degradation at the surface that does not occur in the bulk of the films. Vibrational spectroscopy reveals that the initial photoswitching to the merocyanine state is followed by degradation. We show that the surface sensitivity of the technique used to monitor switching is critical to observing the changes that are responsible for the switching in surface polarity.